Dr. Jeff Masters' WunderBlog

Red River Rising: a Top-Ten Fargo Flood in 4 of the Past 5 Years

By: JeffMasters, 3:44 PM GMT on April 29, 2013

The Red River at Fargo, North Dakota surpassed major flood level on Sunday and continues to rise, with a peak expected Wednesday at the 9th highest flood level observed since 1897. On Friday, the President an emergency declaration for North Dakota because of the flooding, and millions of sandbags have been filled in anticipation of the huge flood. This year will be the fourth time in the past five years that Fargo has experienced a top-ten flood in recorded history. Flood stage is eighteen feet, and the Red River has now reached flood stage at Fargo for an astounding nineteen of the past twenty years, according to the U.S. Army Corps of Engineers. Prior to this remarkable stretch of flooding (which began in 1993), the river flooded in just 29 of 90 years. The Army Corps of Engineers calculates that in the last twenty years, the Red River has had ten 1-in-10 year floods--one every two years, on average. Two of these floods (1997 and 2011) were greater than 1-in-50 year floods, and one (2009) was a 1-in-100 year flood. That year, the Red River hit a record high-water mark of nearly 41 feet, or 23 feet above flood stage. Thousands of people had to leave home for higher ground, and about 100 homes were badly damaged or rendered unlivable. This year's flood will be somewhere between a 1-in-10 year to 1-in-50 year flood. Since a 1-in-10 year flood, historically, has a 10% chance of occurring in a given year, the incidence of flooding along the Red River over the past twenty years has clearly been extraordinarily abnormal.


Figure 1. View of the Red River of the North at the Fargo gauge taken on April 24, 2013 (top) and April 29, 2013 (bottom.) The river rose from 17' on the 24th (flood stage is 18') to 31' on the 29th. Image credit: USGS.

Reasons for this year's flood: unfavorable weather conditions
The USGS cites five weather factors that can act to increase flooding along the Red River. Four out of five of these factors occurred to a significant degree this year:

1) Above-normal amounts of precipitation in the fall of the year that produce high levels of soil moisture, particularly in flat surface areas, in the basin. North Dakota had its 9th wettest fall since 1895 during 2012.

2) Freezing of saturated ground in late fall or early winter, before significant snowfall occurs, that produces a hard, deep frost that limits infiltration of runoff during snowmelt. Fargo had temperatures that hit 50°F on December 2 - 3, 2012, followed by a sudden plunge to below-freezing temperatures that began on December 7. Temperatures remained below freezing the rest of December, and this froze the saturated ground to a great depth.

3) Above-normal winter snowfall in the basin. Fargo received 68.4" of snow during the winter, which is well above the city's average of 50".

4) Above-normal precipitation during snowmelt. Fargo has received 2.06" of precipitation so far this April, compared to the average of 1.23".

5) Above-normal temperatures during snowmelt. Fargo got lucky here. High temperatures in Fargo have been above average only two days during April, on the 26th and 27th.


Figure 2. Current and forecast flood stage for the Red River of the North at Fargo, ND. The river passed major flood stage on Sunday, and is headed for a crest near 35.5' (which is 17.5' above flood stage) on Wednesday. You can access images like these using our wundermap for Fargo with the "USGS River" layer turned on. Click on the icon for USGS station 05054000, then hit the "click for graph" link.

Reasons for flooding: increased urbanization
Urbanization has had a major impact on increasing flooding not only along the Red River, but in every river basin in the U.S. Many cities and developed areas are located in flood plains next to major rivers and their tributaries. Highways, streets, parking lots, sidewalks, and buildings now cover large areas of the ground that used to absorb excess rain water and slow the rate at which run-off from precipitation and melting snow reached rivers. By developing large portions of our flood plains, run-off now reaches rivers more quickly, generating higher floods.

Reasons for flooding: building more levees and flood defenses
Defending ourselves against floods has made floods worse. Every time a new levee is built, or an old flood wall raised in height to prevent overtopping, more and more water is forced into the river bed, which raises the height of the flood. Flood waters that used to be able to spread out over their natural flood plains are now forbidden from spilling out over newly developed land in flood plains. For example, a 2010 proposed improvement to the flood defense system in Fargo could cause a 4 - 10 inch rise in floods immediately downstream from the city, according to the Army Corps of Engineers.


Figure 3. Peak flow of the Red River at Fargo, North Dakota from 1901 - 2012. Three of the top five floods since 1901 have occurred since 2009. The projected crest for 2013 would be the seventh greatest flood since 1897. The U.S. Army Corps of Engineers lists the 10-year flood level for the Red River at Fargo to be 10,300 cubic feet per second (cfs), and a 50-year flood to be 22,300 cfs. A 10-year flood, historically, has a 10% chance of occurring in a given year. In the last twenty years, the Red River has had ten 10-year floods--one every two years, on average. Two of these floods (1997 and 2011) were greater than 1-in-50 year floods, and one (2009) was a 1-in-100 year flood. This year will be the fourth year out of the past five with a greater than 1-in-20 year flood. Image credit: U.S. Geological Survey.

Reasons for flooding: precipitation is increasing
Over the past century, precipitation over the Red River of the North drainage basin in Eastern North Dakota and Western Minnesota has increased by about 15%--more than any other region of the country. This fits the pattern expected by climate change models, which predict that winter and spring precipitation will increase by another 15% by the year 2100 over the Red River of the North drainage basin. As the climate warms, evaporation of moisture from the oceans increases, resulting in more water vapor in the air. According to the 2007 IPCC report, water vapor in the global atmosphere has increased by about 5% over the 20th century, and 4% since 1970. Satellite measurements (Trenberth et al., 2005) have shown a 1.3% per decade increase in water vapor over the global oceans since 1988. Santer et al. (2007) used a climate model to study the relative contribution of natural and human-caused effects on increasing water vapor, and concluded that this increase was "primarily due to human-caused increases in greenhouse gases". This was also the conclusion of Willet et al. (2007).


Figure 4. The colors on the map show annual total precipitation changes (percent) for 1991-2011 compared to the 1901-1960 average, and show wetter conditions in most areas (McRoberts and Nielsen-Gammon 2011). The bars on the graphs show average precipitation differences by decade for 1901-2011 (relative to the 1901-1960 average) for each region. The far right bar is for 2001-2011. (Figure source: NOAA NCDC/CICS-NC. Data from NOAA NCDC.) Note that precipitation over the Red River of the North drainage basin in Eastern North Dakota and Western Minnesota (outlined in red) has increased by about 15%--more than any other region of the country. Image credit: National Climate Assessment Draft, 2013.


Figure 5. Projected seasonal precipitation change for winter and spring (percent) for 2071-2099 (compared to1901-1960) as projected by the climate models used to formulate the 2013 IPCC climate change report, assuming we keep emitting heat-trapping gases like carbon dioxide to the atmosphere at current rates. Teal indicates precipitation increases, and brown, decreases. Hatched areas indicate confidence that the projected changes are large and are consistently wetter or drier. In general, areas that are wet are expected to get wetter, and areas that are dry will get drier. White areas indicate confidence that the changes are small. The Red River Valley is expected to see a precipitation increase of at least 20%, which would lead to bigger and more frequent spring floods. (Figure source: NOAA NCDC / CICS-NC. Data from CMIP5; analyzed by Michael Wehner, LBNL.) Image credit: Preliminary draft of the 2013 U.S. National Climate Assessment report.

A permanent fix for Fargo's flooding problems: a $2 billion diversion canal?
As the population continues to expand, development in flood plains and construction of new levees and flood protection systems will continue to push floods to higher heights. With global warming expected to continue and drive ever higher precipitation amounts--falling preferentially in heavy precipitation events--it is highly probable that flooding in the Red River Valley--and over most of the northern 1/3 of the U.S. where precipitation increases are likely (Figure 5)--will see higher and more frequent spring floods. With these higher and more frequent floods comes the increased risk of multi-billion dollar disasters, when a record flood event overwhelms flood defenses and inundates huge areas of developed flood plains. Obviously, we need to make smart decisions to limit development in flood plains to reduce the cost and suffering of these future flooding disasters.

A permanent fix for Fargo's flooding woes may lie in the construction of a 36-mile long canal that would steer flood waters around Fargo and neighboring Moorhead, Minnesota, according to an April 28, 2013 Associated Press article. The proposed canal could cost $2 billion and take ten years to complete, but has drawn strong opposition from farmers, homeowners and businesses who lie in the path of the proposed diversion channel. The http://www.redriverbasincommission.org/ has the latest long-term options on new flood control options for the Red River.

References
Kunkel, K. E., D. R. Easterling, K. Redmond, and K. Hubbard, 2003, "Temporal variations of extreme precipitation events in the United States: 1895.2000", Geophys. Res. Lett., 30(17), 1900, doi:10.1029/2003GL018052.

Groisman, P.Y., R.W. Knight, T.R. Karl, D.R. Easterling, B. Sun, and J.H. Lawrimore, 2004, "Contemporary Changes of the Hydrological Cycle over the Contiguous United States: Trends Derived from In Situ Observations," J. Hydrometeor., 5, 64.85.

McRoberts, D. Brent, John W. Nielsen-Gammon, 2011, "A New Homogenized Climate Division Precipitation Dataset for Analysis of Climate Variability and Climate Change," J. Appl. Meteor. Climatol., 50, 1187–1199.
doi: http://dx.doi.org/10.1175/2010JAMC2626.1

Milly, P.C.D., R.T. Wetherald, K.A. Dunne, and T.L.Delworth, Increasing risk of great floods in a changing climate", Nature 415, 514-517 (31 January 2002) | doi:10.1038/415514a.

Santer, B.D., C. Mears, F. J. Wentz, K. E. Taylor, P. J. Gleckler, T. M. L. Wigley, T. P. Barnett, J. S. Boyle, W. Brüggemann, N. P. Gillett, S. A. Klein, G. A. Meehl, T. Nozawa, D. W. Pierce, P. A. Stott, W. M. Washington, and M. F. Wehner, 2007, "Identification of human-induced changes in atmospheric moisture content", PNAS 2007 104: 15248-15253.

Trenberth, K.E., J. Fasullo, and L. Smith, 2005: "Trends and variability in column-integrated atmospheric water vapor", Climate Dynamics 24, 741-758.

Willett, K.M., N.P. Gillett, P.D. Jones, and P.W. Thorne, 2007, "Attribution of observed surface humidity changes to human influence", Nature 449, 710-712 (11 October 2007) | doi:10.1038/nature06207.

Links
A good way to track the flooding event is to use our wundermap for the Red River with the USGS River layer turned on.

The Fargo Flood webpage of North Dakota State University, Fargo, has some excellent links.

I'll have a new post on Wednesday at the latest.

Jeff Masters

Flood Climate Change

Updated: 2:15 PM GMT on April 30, 2013

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Dark Snow Project: Crowd-Source Funded Science for Greenland

By: JeffMasters, 3:03 PM GMT on April 26, 2013

"There's no place on Earth that is changing faster--and no place where that change matters more--than Greenland." So said 350.org founder Bill McKibben, in a 2012 Rolling Stone magazine interview. As Earth Week 2013 draws to a close, I want to draw your attention to a unique effort to learn more about why Greenland is melting so fast--a crowd-funded research project that anyone can contribute to, which aims to answer the "burning question": How much does wildfire and industrial soot darken the ice, increasing melt? The Dark Snow Project, the first-ever Greenland expedition relying on crowd-source funding, hopes to raise $150,000 to mount a field research campaign to find out. The project is the brainchild of Dr. Jason Box, Professor at the Geological Survey of Denmark and Greenland (GEUS), and one of the world's leading experts on Greenland's glaciers. He has set up a website called darksnowproject.org to help raise the funds for the field campaign, and has raised about half of the needed amount as of mid-April.


Figure 1. Over the course of several years, turbulent water overflow from a large melt lake carved this 60-foot-deep (18.3 meter-deep) canyon in Greenland's Ice Sheet (note people near left edge for scale). Image credit: Ian Joughin, University of Washington.

2012: Unprecedented melting in Greenland
Watching the weather events of 2012 over Greenland made all seasoned climate watchers a little queasy. The vast ice sheet on the island holds enough water to raise global sea levels by 7.36 meters (24.15 feet) were it all to melt, and the ice melt season of 2012 gave notice that an epic melting of the Greenland Ice Sheet may be underway. According to NOAA's 2012 Arctic Report Card, the duration of melting at the surface of the ice sheet in summer 2012 was the longest since satellite observations began in 1979, and the total amount of summer melting was nearly double the previous record, set in 2010 (satellite records of melting go back to 1979.) A rare, near-ice sheet-wide surface melt event melted 97% of the surface of Greenland's ice sheet on July 11 - 12. While a similar melt event at the summit occurred 1889, but the 1889 event has no basis in the instrumental record from coastal Greenland. It's instead likely that 2012 was Greenland's warmest summer in at least 863 years, since the medieval warm period (see http://www.meltfactor.org/blog/?p=677 and http://www.meltfactor.org/blog/?p=725). The incredibly warm temperatures have been blamed on highly unusual atmospheric circulation and jet stream changes, which were also responsible for 2012's unusually wet summer weather in England. It would not be a surprise if this sort of summer began occurring more often, since temperatures on top of the Greenland Ice Sheet have been rising six times faster than the global average during the past twenty years. A May 2013 Geophysical Research Letters paper by McGrath et al., "Recent warming at Summit, Greenland: Global context and implications", concluded that by 2025, there is a 50% chance of ice sheet-wide melt events happening annually. The ice sheet reached its darkest value on record in 2012. The darkened surface was due to below average summer snow, soot particles from pollution and forest fires, and record melting. A darker ice sheet absorbs more solar energy, in a vicious cycle that raises temperatures, melts more ice, and further darkens the ice sheet. The amount of melting that was caused by soot from forest fires is important to know, since global warming is likely to increase the amount of forest fires in coming decades. However, the amount of forest fire soot landing on the Greenland Ice Sheet is almost completely unknown, which is why Dr. Box is determined to find out, via the Dark Snow Project.


Figure 2. Smoke from a fire in Labrador, Canada wafts over the Greenland ice sheet on June 17, 2012, as seen in this cross-section view of aerosol particles taken by NASA's CALIPSO satellite. Image credit: Dr. Jason Box, Ohio State University.

Greenland causing 25% of global sea level rise
In a landmark study published in November 2012 in Science, 47 researchers from 26 laboratories reported that the amount of ice being lost from Greenland and Antarctica has tripled since the 1990s, with Greenland contributing more than twice as much to global sea level rise than Antarctica. The study, "A Reconciled Estimate of Ice-Sheet Mass Balance", found that the two ice sheets were responsible for 20% of the global sea level rise of 3.1 mm/year during the 20-year period 1992 - 2011. The remainder of the rise was due to expansion of the water due to heating of the oceans, melting of mountain glaciers, and unsustainable pumping of ground water. Said co-author Erik Ivins of NASA's Jet Propulsion Laboratory, "The pace of ice loss from Greenland is extraordinary, with nearly a five-fold increase since the mid-1990s." As of 2011, Greenland's contribution to global sea level rise on its own had risen to 20 - 25%, according to an international research group led by the GFZ German Research Centre for Geosciences, in an article published in Earth and Planetary Science Letters on 1 June 2012. If the current exponential ice loss trends continue for the next ten years, Greenland's contribution to sea level rise will double to 1.4 mm/yr by 2022, the researchers said. Many sea level rise researchers expect global sea level to rise by about 1 meter (3.3 feet) by 2100. During the 20th century, global sea level rise was about 0.18 meters (7 inches.)


Figure 3. Monthly smoothed (purple) and unsmoothed (blue) values of the total mass lost from the Greenland Ice Sheet (in Gigatons, Gt) from measurements by the GRACE satellites between March 2002-September 2012. An approximate equivalent global sea level rise figure is on the right axis. Note that the decline in ice mass lost from Greenland is not a straight line--it is exponential, meaning that more ice loss is lost each year than in the previous year. Image credit: 2012 Arctic Report Card.

Will Antarctica be more important than Greenland for sea level rise?
Although melting from Greenland is currently raising global sea level by about a factor of two more than Antarctica melting is, that situation may change later this century. A 2013 study by Dahl-Jensen et al. looked at a new ice core drilled from the bottom-most depths of the Greenland Ice Sheet. The core suggests that the ice in Greenland may have partially survived the warm Eemian period before the Ice Age, approximately 118,000 - 126,000 years ago, when Greenland temperatures were 5- 8°C warmer than present-day temperatures. Global sea level during the Eemian was 4 - 8 meters (13 - 26 ft) higher than the present sea level, and the scientists estimated that melting from Greenland was responsible for 2 meters (6.6 ft) of this sea level rise. This implies that Antarctica was responsible for 50 - 75% of global sea level rise during the Eemian, and thus we might expect Antarctica to take over as the dominant source of sea level rise later this century, when global temperatures may to rise to levels similar to those experienced during the Eemian.

Related posts
Greenland experiences melting over 97% of its area in mid-July (July 25, 2012)
Record warmth at the top of the Greenland Ice Sheet (July 18, 2012)
Unprecedented May heat in Greenland; update on 2011 Greenland ice melt (May, 2012)
Greenland update for 2010: record melting and a massive calving event

Dr. Jason Box's blog on Greenland and the Dark Snow Project is at http://www.meltfactor.org.

The http://www.greenlandmelting.com/ website looks like a great resource for following this year's melt progression in Greenland.


Video 1. Glaciologist Dr. Jason Box and 350.org founder Bill McKibben plug the Darksnow project in this January 2013 video by Peter Sinclair. There's some impressive footage of the record Greenland snow melt of summer 2012 sweeping away a 20-ton tractor that was attempting to repair a bridge washed out by the raging Watson River on July 11, 2012 in Kangerlussauaq, Greenland. The driver escaped unharmed.

Support the Dark Snow Project
One of Dr. Box's collaborators, photographer James Balog, who created the amazing time-lapse Greenland glacier footage in the fantastic 2012 "Chasing Ice" movie, puts it like this: "Working in Greenland these past years has left me with a profound feeling of being in the middle of a decisive historic moment--the kind of moment, at least in geologic terms, that marks the grand tidal changes of history." On that note, I encourage you all to support the Dark Snow Project. Have a great weekend, everyone!

Dark Snow Project Expedition Plan 2013
Prepare and gather science equipment including a field spectrometer, snow and ice coring device, and snow metrics kit.

Travel to Iqualuit, on Baffin Island, Nunavut from home locales in California, Ohio, Michigan, Vermont and rendezvous with Dash-6 "Twin Otter" ski-equipped airplane and flight crew.

Organize cold weather survival kit.

Ferry team from Iqualuit to Kangerlussuaq, Greenland.

Fly to and land at sampling sites high on the inland ice sheet.

At each site collect snow samples from a snow pit and obtain snow cores to a minimum depth of the previous year's snow surface, and record snow properties.

Transport of team and snow samples to Greenland's capital Nuuk, where the team will rest after hustling at field sites.

Return to Iqualuit, then to respective home locales to start the data analysis and reporting phase of campaign.

Jeff Masters

Glaciers Climate Change

Updated: 8:13 PM GMT on June 18, 2013

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Unusually cold spring in Europe and the Southeast U.S. due to the Arctic Oscillation

By: JeffMasters, 2:52 PM GMT on April 25, 2013

During March 2013, residents of Europe and the Southeast U.S. must have wondered what happened to global warming. Repeated bitter blasts of bitter cold air invaded from the Arctic, bringing one of the coldest and snowiest Marches on record for much of northern Europe. In the U.K., only one March since 1910 was colder (1962), and parts of Eastern Europe had their coldest March since 1952. A series of exceptional snowstorms struck many European locations, including the remarkable blizzard of March 11 - 12, which dumped up to 25 cm (10”) of snow on the Channel Islands of Guernsey and Jersey in the U.K., and in the northern French provinces of Manche and Calvados. The entire Southeast U.S. experienced a top-ten coldest March on record, with several states experiencing a colder month than in January 2013. Despite all these remarkable cold weather events, global temperatures during March 2013 were the 9th warmest since 1880, said NASA. How, then, did such cold extremes occur in a month that was in the top 8% of warmest Marches in Earth's recorded history? The answer lies in the behavior of the jet stream. This band of strong high-altitude winds marks the boundary between cold, polar air and warm, subtropical air. The jet stream, on average, blows west to east. But there are always large ripples in the jet, called planetary waves (or Rossby waves.) In the Northern Hemisphere, cold air from the polar regions spills southward into the U-shaped troughs of these ripples, and warm air is drawn northwards into the upside-down U-shaped ridges. If these ripples attain unusually high amplitude, a large amount of cold polar air will spill southwards into the mid-latitudes, causing unusual cold extremes. This was the case in Europe and the Eastern U.S. in March 2013. These cold extremes were offset by unusually warm conditions where the jet stream bulged northwards--over the Atlantic, the Western U.S., and in China during March 2013. In fact, the amplitude of the ripples in the jet stream reached their most extreme value ever recorded in any March during 2013, as measured by an index called the Arctic Oscillation (AO).


Figure 1. The monthly Arctic Oscillation (AO) index from 1950 - March 2013 shows that three of the six most extreme negative cases have occurred since 2009. Note that all of the six most negative AO indices on record were associated with historic cold waves and blizzards over Europe or the Eastern U.S. Image created using data from NOAA's Climate Prediction Center.

Measuring the jet stream's contortions: the Arctic Oscillation (AO)
One measure of how extreme the ripples in the jet stream are is by measuring the difference in pressure between the Icelandic Low and the Azores High. An index based in this pressure difference is called the North Atlantic Oscillation (NAO). When this index is strongly negative, it means that the pressure difference between the Icelandic Low and the Azores High is low. This results in a weaker jet stream, allowing it to take large, meandering loops. These loops allow cold air to spill far to the south from the Arctic into the mid-latitudes. A more general index that looks at pressure patterns over the entire Arctic, not just the North Atlantic, is called the Arctic Oscillation (AO). The AO and NAO are closely related about 90% of the time. According to a 2010 paper by L'Heureux et al., a strongly negative AO pattern that allows cold air to spill southwards into the mid-latitudes does nothing to the average temperature of the planet. Fluctuations in the jet stream as measured by the AO simply act to redistribute heat. It's kind of like turning off your refrigerator and leaving the refrigerator door open--the cold air from the refrigerator spills out into the room, but is replaced inside the refrigerator by warm room air. No net change in heat occurs. During March 2013, the AO index hit -3.2. Not only was this the most extreme negative March value of the AO since record keeping began in 1950, it was also the sixth lowest AO index ever measured. It was also the first time the AO index had been that extremely negative in a non-winter month (because the circulation patterns are stronger in the winter, we tend to see more extreme values of the AO index in December, January, and February.) This unusual contortion of the jet stream in March 2013 allowed Europe to have exceptional cold weather in a month when the global average temperature was among the warmest 8% of Marches on record. Why did the AO index get so extreme in March 2013? Part of the blame goes to the sudden stratospheric warming event that began in January (wunderblogger Lee Grenci has a detailed post on this event.) Sudden stratospheric warming events tend to push the atmosphere into a more negative AO configuration. Another major factor was the very active Madden Julian Oscillation (MJO), a pattern of increased thunderstorm activity near the Equator that moves around the globe in 30 - 60 days. When the area of increased thunderstorms associated with the MJO is located in the Pacific Ocean, as occurred during much of March 2013, this tends to create negative AO conditions. Finally, wintertime Arctic sea ice loss has been tied to more negative AO patterns, and sea ice was well blow average again during March.


Figure 2. The Arctic Oscillation (AO) is a pattern of varying pressure and winds over the Northern Hemisphere that can strongly influence mid-latitude weather patterns. When the AO is in its positive phase, jet stream winds are strong and the jet stream tends to blow mostly west to east, with low-amplitude waves (troughs and ridges.) Since the jet stream marks the boundary between cold Arctic air to the north and warm subtropical air to the south, cold air stays bottled up in the Arctic. When the AO is in its negative phase, the winds of the jet stream slow down, allowing the jet to take on more wavy pattern with high-amplitude troughs and ridges. High amplitude troughs typically set up over the Eastern U.S. and Western Europe during negative AO episodes, allowing cold air to spill southwards in those regions and create unusually cold weather.

Are jet stream patterns getting more extreme?
We've had some wildly variable jet stream patterns in recent years in the Northern Hemisphere. Just last year, we had a strongly positive AO in March, when our ridiculous "Summer in March" heat wave brought the warmest March on record to the U.S. The first day of spring in Chicago, IL on March 20, 2013 had a high temperature of just 25°F--a 60 degree difference from last year's high of 85°F on March 20! During the past five years, we've set new monthly records for extreme negative AO index for six of the twelve months of the year:

-4.3: February 2010
-3.4: December 2009
-3.2: March 2013
-1.5: October 2009, 2012
-1.4: June 2009
-1.4: July 2009

Note that four of these months with an extremely negative AO occurred in one year--2009. This unusual event was "unprecedented in the 60-year record", according to L'Heureux et al. (2010.) Despite the unusually large negative AO in 2009, the authors found that the AO index between 1950 - 2009 had actually trended to be more positive, in both the winter and annual mean. This is in agreement with what many climate models predict: the AO index should get increasingly positive, due to increasing levels of CO2 in the atmosphere, since this tends to make the stratosphere cool and increase the strength of high altitude winds over the Arctic. However, a number of papers have been published since 2009 theorizing that the record loss of Arctic sea ice in recent years may be significantly altering Northern Hemisphere jet stream patterns (I list eleven of these papers below.) Many of these studies show a link between Arctic sea ice loss and an increasingly negative AO and NAO index in winter. Dr. Jennifer Francis of Rutgers has authored several of these papers, and wrote a very readable explanation of the theory linking Arctic sea ice loss to extreme weather in the mid-latitudes for our Earth Day 2013 microsite. Her post was called, "The Changing Face of Mother Nature." The most recent technical paper connecting Arctic sea ice loss to extreme weather was a March 2013 paper by Tang et al., "Cold winter extremes in northern continents linked to Arctic sea ice loss". The paper argued that unusual jet stream contortions in winter have become increasingly common in recent years. The scientists found a mathematical relationship between wintertime Arctic sea ice loss and the increase in unusual jet stream patterns capable of bringing cold, snowy weather to the Eastern U.S., Western Europe, and East Asia, typical of what one sees during a strongly negative Arctic Oscillation. They theorized that sea ice loss in the Arctic promotes more evaporation, resulting in earlier snowfall in Siberia and other Arctic lands. The earlier snow insulates the soil, allowing the land to cool more rapidly. This results in a southwards shift of the jet stream and builds higher atmospheric pressures farther to the south, which increases the odds of cold spells and blocking high pressure systems that can cause extended periods of unusually cold and snowy weather in the mid-latitudes. The research linking climate change impacts in the Arctic to more extreme jet stream patterns is still very new, and we need several more years of data and additional research before we can be confident that this is occurring. But if the new research is correct, the crazy winter weather we've been seeing since 2009 may be the new normal in a world with rapid warming occurring in the Arctic.


Video 1. Using jet stream animations created by NOAA's Visualiation Laboratory, Dr. Jennifer Francis of Rutgers explains why the jet stream exists, and how the warming of the Arctic may be changing it.

Related posts
"The Changing Face of Mother Nature" by Dr. Jennifer Francis of Rutgers, April 22, 2013.
Why was the start to spring 2013 so cold? by the UK Met Office, April 2013.
Extreme jet stream causing record warmth in the east, record cold in the west (January 2013)
Arctic sea ice loss tied to unusual jet stream patterns (April 2012)
Our extreme weather: Arctic changes to blame? (December 2011)
Florida shivers; Hot Arctic-Cold Continents pattern is back (December 2010)
Jet stream moved northwards 270 miles in 22 years; climate change to blame? (June 2008)
Linking Weird Weather to Rapid Warming of the Arctic by Dr. Jennifer Francis of Rutgers University (March 2012)
From Heat Wave to Snowstorms, March Goes to Extremes by Andrew Freedman of Climate Central (March 2013)

References
L'Heureux, M., A. Butler, B. Jha, A. Kumar, and W. Wang (2010), Unusual extremes in the negative phase of the Arctic Oscillation during 2009, Geophys. Res. Lett., 37, L10704, doi:10.1029/2010GL043338.

Papers published since 2009 that link Arctic sea ice loss to an increase in negative AO or NAO conditions
Deser, C., R. Tomas, M. Alexander, and D. Lawrence (2010), "The seasonal atmospheric response to projected Arctic sea ice loss in the late 21st century," J. Clim., 23, 333–351, doi:10.1175/2009JCLI3053.1.

Francis, J.A., and S.J. Vavrus (2012), "Evidence linking Arctic amplification to extreme weather in mid-latitudes," Geophysical Research Letters, 21 February, 2012.

Francis, J. A., W. Chan, D. J. Leathers, J. R. Miller, and D. E. Veron, 2009, "Winter northern hemisphere weather patterns remember summer Arctic sea-ice extent," Geophys. Res. Lett., 36, L07503, doi:10.1029/2009GL037274.

Honda, M., J. Inoue, and S. Yamane, 2009, "Influence of low Arctic sea-ice minima on anomalously cold Eurasian winters," Geophys. Res. Lett., 36, L08707, doi:10.1029/2008GL037079.

Jaiser, R., K. Dethloff, D. Handorf, A. Rinke, J. Cohen (2012), "Impact of sea ice cover changes on the Northern Hemisphere atmospheric winter circulation", Tellus A 2012, 64, 11595, DOI: 10.3402/tellusa.v64i0.11595

Liu et al. (2012), "Impact of declining Arctic sea ice on winter snowfall", Proc. Natl. Academy of Sciences, Published online before print February 27, 2012, doi: 10.1073/pnas.1114910109

Overland, J. E., and M. Wang, 2010, "Large-scale atmospheric circulation changes associated with the recent loss of Arctic sea ice," Tellus, 62A, 1.9.

Petoukhov, V., and V. Semenov, 2010, "A link between reduced Barents-Kara sea ice and cold winter extremes over northern continents," J. Geophys. Res.-Atmos., ISSN 0148-0227.

Seager, R., Y. Kushnir, J. Nakamura, M. Ting, and N. Naik (2010), "Northern Hemisphere winter snow anomalies: ENSO, NAO and the winter of 2009/10," Geophys. Res. Lett., 37, L14703, doi:10.1029/2010GL043830.

Seierstad, I. A., and J. Bader (2009), "Impact of a projected future Arctic Sea Ice reduction on extratropical storminess and the NAO," Clim. Dyn., 33, 937-943, doi:10.1007/s00382-008-0463-x.

Tang et al., "Cold winter extremes in northern continents linked to Arctic sea ice loss," Environ. Res. Lett. 8 014036 doi:10.1088/1748-9326/8/1/014036

Jeff Masters

Winter Weather Extreme Weather Climate Change

Updated: 8:22 PM GMT on October 31, 2013

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March 2013 the globe's 10th warmest March; a billion-dollar U.S. weather disaster

By: JeffMasters, 1:56 PM GMT on April 24, 2013

March 2013 was the globe's 10th warmest March since records began in 1880, according to NOAA's National Climatic Data Center (NCDC). NASA rated it the 9th warmest March on record. The year-to-date period of January - March has been the 8th warmest such period on record. March 2013 global land temperatures were the 11th warmest on record, and global ocean temperatures were the 9th warmest on record. March 2013 was the 337th consecutive month with global temperatures warmer than the 20th century average. Global satellite-measured temperatures in March 2013 for the lowest 8 km of the atmosphere were 12th or 8th warmest in the 35-year record, according to Remote Sensing Systems and the University of Alabama Huntsville (UAH), respectively. The Northern Hemisphere snow cover extent during March 2013 was the 16th largest in the 47-year period of record. Wunderground's weather historian, Christopher C. Burt, has a comprehensive post on the notable weather events of March 2013 in his March 2013 Global Weather Extremes Summary. He notes that one nation set an all-time heat record: on March 6th, Navrongo, Ghana reached 43.0°C (109.4°F), the warmest temperature reliably ever measured in the country (for any month.)


Figure 1. March 2013 was the 2nd coldest winter in the U.K. since 1910, exceeded only by March 1962. In this photo taken by wunderphotographer tonylathes on March 24, 2013, we see one of March's heavy snowstorms that affected Wardlow Village in Derbyshire, United Kingdom.


Figure 2. Departure of temperature from average for March 2013, the 10th warmest March for the globe since record keeping began in 1880. The Arctic Oscillation (AO), a large-scale climate pattern that can influence temperatures in the Northern Hemisphere, set a record low for March. This negative phase was associated with frigid Arctic air spilling southward into the Northern Hemisphere middle latitudes, leading to unusually cold conditions in the Eastern U.S., most of Europe, and northern Siberia.This phase of the AO also contributed to much warmer than average and even record warm temperatures in northeastern Canada and southeastern Greenland. A large swath of China and several regions in central and northern Africa in the 0°–20°N latitude belt were also record warm. Image credit: National Climatic Data Center (NCDC) .

First U.S. billion-dollar weather disaster of 2013: March 18 - 20 severe weather outbreak
Two billion-dollar weather disasters occurred globally in March, bringing the 2013 total to five, according to the March 2013 Catastrophe Report from insurance broker AON Benfield. The five billion-dollar weather disasters for 2013 so far:

1) Flooding in Indonesia, 1/20 - 1/27, $3.31 billion
2) Flooding in Australia, 1/21 - 1/30, $2.5 billion
3) Winter weather in Europe, 3/12 - 3/31, $1.8 billion
4) Drought in Central and Eastern China, 1/1 - 3/31, $1.71 billion
5) Severe weather in the Midwest U.S., 3/18 - 3/20, $1 billion

The first billion-dollar weather disaster in the U.S. was a severe weather outbreak that began on March 18, featuring a long-lived squall line of severe thunderstorms called a "derecho" that dropped hail up to softball size from Louisiana to South Carolina. Mississippi was hardest hit, with up to 60,000 insurance claims. Ten tornadoes touched down and two fatalities were reported during the outbreak. The U.S. has averaged 4.4 billion-dollar weather disasters per year from 1980 - 2012, but experienced 25 in the two-year period 2011 - 2012.

The deadliest March weather disaster was an outbreak of severe weather that swept across parts of eastern Bangladesh on March 22. The outbreak included a tornado that struck the regions of Sadar, Akhaura and Bijoynagar in Brahmanbaria district. At least 35 people were killed and 388 injured.


Figure 3. Hail up to the size of tennis balls fell on McComb, Mississippi, as documented by wunderphotographer sirencall On March 18, 2013. The hailstorm was part of a severe weather outbreak that gave the U.S. its first billion-dollar weather disaster of 2013.

Neutral El Niño conditions continue in the equatorial Pacific
For the 12th month in row, neutral El Niño conditions existed in the equatorial Pacific during March 2013. NOAA's Climate Prediction Center (CPC) expects neutral El Niño conditions to last through summer. The large majority of the El Niño models predict neutral conditions will last through the fall of 2013. Temperatures in the equatorial Eastern Pacific need to be 0.5°C below average or cooler for three consecutive for a La Niña episode to be declared; sea surface temperatures were 0.1°C below average as of April 22, and have been +0.1 to -0.4°C from average since March 1, 2013.

Arctic sea ice falls to 5th lowest March extent on record
Arctic sea ice extent during March reached its fifth lowest extent in the 35-year satellite record, according to the National Snow and Ice Data Center (NSIDC). This was the 10th consecutive March and 142nd consecutive month with below-average Arctic sea ice extent. The last ten years (2004 to 2013) have seen nine of the ten lowest March extents in the satellite record.

Jeff Masters

Climate Summaries

Updated: 2:19 PM GMT on April 24, 2013

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Damaging major flooding in Illinois as Mississippi River crests

By: JeffMasters, 2:48 PM GMT on April 23, 2013

The mighty Mississippi River has surged to damaging major flood heights along a 200-mile stretch in western Illinois just north of St. Louis, Missouri. “We have seen some of the worst flooding damage to neighborhoods and homes across our state in Illinois history,” Governor Quinn said on Monday, and he declared 44 counties disaster areas. Missouri Governor Jay Nixon declared a state of emergency after flash flooding hit many areas of his state. The river has been closed to barge traffic along a 15-mile stretch near St. Louis since Saturday, when 114 barges broke loose from a fleeting area. Eleven barges containing coal sank. Approximately twelve locks on the Mississippi and Illinois rivers have been closed to shipping due to high water. The Mississippi River peaked at top-five flood heights in recorded history Sunday through Tuesday along the 200-mile section north of St. Louis, but is now falling. The flood crest has yet to come from St. Louis southwards, where the river will stay near crest for multiple days, due to 0.5 - 1.0" of rain expected to fall over most of Illinois, Missouri, and Indiana on Tuesday and Wednesday. However, the floods will not be as significant, ranking near the 10th highest floods on record near St. Louis. Flood records along the Mississippi extend back in time to the 1840s to 1940s, depending upon the location.


Figure 1. Thursday, April 18, 2013: Aerial photo provided by the U.S. Coast Guard shows the dam in Marseilles, Ill., after seven barges broke free from a tow and came to rest against the dam. (AP Photo/Courtesy of the U.S. Coast Guard, Petty Officer 3rd Class John Schleicher.)

Record flooding ends in Illinois and Michigan
The National Weather Service recognizes four types of flooding: minor, moderate, major, and record. Major flooding is capable of causing significant damage, and moderate and minor flooding generally only cause isolated damage. Record flooding, of course, can cause record damage, and we had at least nineteen river gauges report record flooding during the April 2013 flood event. The record flooding has ended, and no more record flooding is expected this week. The record floods, as compiled by Dr. Greg Forbes of TWC:

Illinois River: at Peoria, IL; Henry IL; Morris IL; Ottawa IL; and LaSalle IL
Grand River at Comstock Park, MI
Rock River at Moline IL and Byron, IL (short record at the latter)
LaMoine River at Ripley, IL and Colmar, IL
Fox River at McHenry Lock and Dam, IL and Algonquin Tailwater, IL
Des Plaines River at Des Plaines and Riverside IL
Vermilion River at Leonore, IL
East Branch DuPage River at Bolingbrook, IL
Spoon River at Seville, IL
English River at Kalona, IA
North Branch Chicago River in Chicago, IL 


Figure 2. Holy carp! A smallmouth bass checks out the interior of an office building in Riverfront Plaza, which was flooded by the Grand River in downtown Grand Rapids, MI, on Saturday, April 21, 2013. The Grand Rapids Public Museum is in the background. The picture was taken by Lynn Clay, director of network office supervision at Northwestern Mutual Financial Network in Grand Rapids. According to an interview with MLive.com, she was simply trying to take a photo of the flood when the fish swam into the frame. She didn’t even realize it until she saw the image later. The 110-year-old building, despite some leaking and soggy bottom level carpeting, survived the flooding in great shape, according to facilities staff.


Figure 3. Office building in Grand Rapids, Michigan where the fish photo was taken, as seen on Saturday, April 21, 2013. Image credit: GRNow.com. According to this thread on Facebook, the office building was built with aquarium glass.

More major Midwest spring flooding expected next week
A second round of major Midwest flooding is expected the last week of April and into early May, when the heavy snowpack in North Dakota, South Dakota, Minnesota, and Wisconsin is expected to melt significantly, unleashing the equivalent of 4 - 8 inches of rainfall into the watersheds of the Red River of the North, Mississippi River, and Missouri River. Of particular concern is the flooding expected on the Red River of the North near Fargo, North Dakota, where flood heights will likely be among the top five in recorded history. Fortunately, the latest 2-week forecast from the GFS model shows only one significant rain-making storm affecting the region April 25 - May 7--a cold front that may produce about 0.5" of precipitation around April 30.

Wunderground's weather historian Christopher C. Burt summarized some of the rainfall and flooding records from the epic storm April 15 - 20 storm in his Sunday post.

Earth Week 2013
The general public think less than half of climate scientists agree that humans are causing global warming. The reality is 97%. Dr. John Cook, Climate Change Communication Fellow for the Global Change Institute at the University of Queensland, explains the challenges of climate science communication in his contribution to our Earth Day 2013 microsite, "Closing the Consensus Gap on Climate Change."

Jeff Masters

Flood

Updated: 9:15 PM GMT on April 23, 2013

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Mother Nature's face is not aging slowly or gracefully

By: JeffMasters, 2:49 PM GMT on April 22, 2013

"Mother Nature's face is not aging slowly or gracefully, the wrinkles and scars caused by accumulating greenhouse gases are already visible. The good news? Extreme weather is also chiseling fissures and gaping holes in the climate deniers' bunker, leaving a crumbling foundation for their arguments. Moving on, it's time to prepare for the unusual weather ahead that is likely to become usual." So writes Dr. Jennifer Francis of Rutgers in her short essay for Earth Day 2013, "The Changing Face of Mother Nature." Dr. Francis' piece is part of a special Earth Day 2013 microsite wunderground has put together, featuring original short essays from seven of the planet's leading climate scientists and climate science communicators. Today is a day to appreciate our planet which sustains all life, a day to reflect on its beauty, and a day to draw attention to the challenges we face to maintain a livable environment for our steadily growing population. Below is a short synopsis of our seven contributors' work.


Figure 1. My favorite wunderphoto of 2012: high-level cirrus clouds containing ice crystals act as prisms, creating this beautiful "Sky Painting" captured by wunderphotographer Doesiedoats over Williams, Oregon on August 7, 2012. As is my tradition on Earth Day, I provide links at the bottom of my Earth Day post to my favorite wunderphotos taken by the wunderground community over the past year. Keep on looking up and sharing your view of the sky!

The Increased Risk of Drought under Global Warming
Drought is the greatest threat civilization faces from climate change, because drought affects the two things we need to live--food and water. Drought expert Dr. Aiguo Dai of SUNY Albany reviews the latest drought predictions from climate models and their "dire projection of increased risk of severe droughts," in his piece, "The Increased Risk of Drought under Global Warming".

The Changing Face of Mother Nature
It seem as though the weather gods have gone berserk in recent years, as nearly every day the headlines report unusual droughts, floods, prolonged cold and snow, heat waves, or unusual weather events happening somewhere around the globe. Dr. Jennifer Francis of Rutgers explains how the unprecedented melting of sea ice and snow in the Arctic may be contributing to this onslaught in her contribution, "The Changing Face of Mother Nature."

My Climate Change
"I used to be very skeptical about global warming, unconvinced that humans had anything to do with it or that it was affecting the weather," writes Stu Ostro, Senior Meteorologist for The Weather Channel. "But then that changed." Find out why he changed his mind in his piece, "My Climate Change."

Closing the Consensus Gap on Climate Change
The general public think less than half of climate scientists agree that humans are causing global warming. The reality is 97%. Dr. John Cook, Climate Change Communication Fellow for the Global Change Institute at the University of Queensland, explains the challenges of climate science communication in his contribution, "Closing the Consensus Gap on Climate Change."

The Arctic's Shrinking Sea Ice Cover
The emerging view is that the Arctic will lose essentially all of its summer sea ice cover by the end of this century, perhaps as early as 2030-2040. Dr. Mark Serreze, Director of the National Snow and Ice Data Center, discusses the implications in his post, "The Arctic's Shrinking Sea Ice Cover."

How Do We Know Humans are Responsible for Global Warming?
We know Earth is warming, but how do we know that human activities are primarily responsible? Dr. Michael Mann of Penn State explains the evidence in his contribution, "How Do We Know Humans are Responsible for Global Warming?"

Is This Global Warming?
Lately, whenever there is a severe weather or climate event that causes a lot of damage - like a severe heatwave, drought, hurricane or tornado - scientists are asked some version of the question, "Is this global warming?" Dr. Noah Diffenbaugh of Stanford University explains what climate science can and cannot say about the answer to this question in his piece, "Is This Global Warming?"

Other Earth Day contributions
Wunderground Community member Skyepony has contributed a piece called "Earth Day 2013: Waiting to Get Fracked."

A new documentary called Thin Ice follows scientists at work in the Arctic, Antarctic, Southern Ocean, New Zealand, Europe and the USA.  They talk about their work, and their hopes and fears, with a rare candor and directness. This creates an intimate portrait of the global community of researchers racing to understand our planet's changing climate. Over 100 college campuses and art theaters are hosting screenings this week.

Jeff Masters

Climate Change

Updated: 2:55 PM GMT on April 22, 2013

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Extreme Drought to Extreme Flood: Weather Whiplash Hits the Midwest

By: JeffMasters, 2:42 PM GMT on April 19, 2013

It seems like just a few months ago barges were scraping bottom on the Mississippi River, and the Army Corps of Engineers was blowing up rocks on the bottom of the river to allow shipping to continue. Wait, it was just a few months ago--less than four months ago! Water levels on the Mississippi River at St. Louis bottomed out at -4.57' on January 1 of 2013, the 9th lowest water level since record keeping began in 1861, and just 1.6' above the all-time low-water record set in 1940 (after the great Dust Bowl drought of the 1930s.) But according to National Weather Service, the exceptional April rains and snows over the Upper Mississippi River watershed will drive the river by Tuesday to a height 45 feet higher than on January 1. The latest forecast calls for the river to hit 39.4' on Tuesday, which would be the 8th greatest flood in history at St. Louis, where flood records date back to 1861. Damaging major flooding is expected along a 250-mile stretch of the Mississippi from Quincy, Illinois to Thebes, Illinois next week. At the Alton, Illinois gauge, upstream from St.Louis, a flood height of 34' is expected on Tuesday. This would be the 6th highest flood in Alton since 1844, and damages to commercial property in the town of Alton occur at this water level. In addition, record flooding is expected on at least five rivers in Illinois and Michigan over the next few days. A crest 1.5' above the all-time record has already occurred on the Des Plaines River in Chicago. This river has invasive Asian Carp that could make their way into Lake Michigan if a 13-mile barrier along the river fails during an extreme flood. Fortunately, NPR in Michigan is reporting today that U.S. Army Corps of Engineers crews stationed along the 13-mile Asian carp barrier have seen no evidence of the fish breaching the structure, and it would have taken a flood much larger than today's record flood to breach the structure. A crest on the Grand River in Grand Rapids, Michigan nearly 4' above the previous record (period of record: at least 113 years) is expected this weekend. At this flood level, major flooding of residential areas is expected, though the flood wall protecting downtown Grand Rapids will keep the commercial center of the city from flooding.


Figure 1. The rains that fell in a 24-hour period ending at 7 am EDT Thursday, April 18, 2013 over Northern Illinois were the type of rains one would expect see fall only once every 40 years (yellow colors), according to METSTAT, Inc. (http://www.metstat.com.) METSTAT computed the recurrence interval statistics based on gauge-adjusted radar precipitation and frequency estimates from NOAA Atlas 14 Volume 2, published in 2004 (http://dipper.nws.noaa.gov/hdsc/pfds/.) METSTAT does not supply their precipitation recurrence interval forecasts or premium analysis products for free, but anyone can monitor the real-time analysis (observed) at: http://metstat.com/solutions/extreme-precipitation-index-analysis/

Damages from the April 2013 Midwest U.S. flood in Illinois, Michigan, and Missouri are likely to run into the hundreds of millions of dollars. Some of the impacts at the flood levels predicted include:

St. Louis, MO:
Major flooding begins. At this level the Choteau Island Levee, protecting 2400 acres, is overtopped. Also, Lemay Park just south of Lemay Ferry Road will begin flood

Cape Girardeau, MO:
Many homes in the Cape Girardeau area are affected and evacuations may be required. Over 100,000 acres is flooded. Numerous roads are closed.

Hannibal, MO:
The Sny Island and South Quincy levees are overtopped between River Mile 315.4 and 264.3, flooding 110,000 acres. The South River levee is overtopped between River Mile 320.5 and 312.1, flooding 10,000 acres.

Quincy, IL:
Missouri Highway 168 east of Palmyra near the BASF plant closes; Quincy Waterworks inundated.

Note that sandbagging efforts may be able to prevent some of these flooding impacts from occurring. Wunderground's weather historian Christopher C. Burt discusses the latest rainfall and flooding records from this week's epic storm in his latest post. He plans on an update Friday afternoon.


Figure 2. Water levels on the Mississippi River at St. Louis are predicted to crest at 39.5', near major flood stage, on Tuesday. This would be the 8th greatest flood in history at St. Louis. Records at the St. Louis gauge to back to 1861. Image credit: National Weather Service.


Figure 3. Water levels on the Mississippi River at St. Louis bottomed out at -4.57' on 01/01/2013, the 9th lowest water level since record keeping began in 1861, and just 1.6' above the all-time low-water record set in 1940, after the great Dust Bowl drought of the 1930s. Image credit: National Weather Service.

Flood-Drought-Flood Weather Whiplash
Residents along the Mississippi River have experienced a severe case of flood-drought-flood weather whiplash over the past two years. The Mississippi reached its highest level on record at New Madrid, Missouri on May 6, 2011, when the river crested at 48.35'. Flooding on the Mississippi and Missouri rivers that year cost an estimated $5 billion. The next year, after the great drought of 2012, the river had fallen by over 53' to an all time record low of -5.32' on August 30, 2012. Damage from the great drought is conservatively estimated at $35 billion. Next Tuesday, the river is expected to be at flood stage again in New Madrid, 40' higher than the August 2012 record low. Now, that is some serious weather whiplash. I'm often asked about the seemingly contradictory predictions from climate models that the world will see both worse floods and worse droughts due to global warming. Well, we have seen a classic example in the Midwest U.S. over the past two years of just how this kind of weather whiplash is possible. A warmer atmosphere is capable of bringing heavier downpours, since warmer air can hold more water vapor. We saw an example of this on Thursday morning, when an upper air balloon sounding over Lincoln, Illinois revealed near-record amounts of moisture for this time of year. The precipitable water--how much rain could fall if one condensed all the water vapor in a column above the ground into rain--was 1.62", just barely short of the Illinois April record for precipitable water of 1.64" set on April 20, 2000 (upper air records go back to 1948.) Thursday's powerful low pressure system was able to lift that copious moisture, cool it, and condense it into record rains. So how can you have worse droughts with more moisture in the air? Well, you still need a low pressure system to come along and wring that moisture out of the air to get rain. When natural fluctuations in jet stream patterns take storms away from a region, creating a drought, the extra water vapor in the air won't do you any good. There will be no mechanism to lift the moisture, condense it, and generate drought-busting rains. The drought that ensues will be more intense, since temperatures will be hotter and the soil will dry out more.

The new normal in the coming decades is going to be more and more extreme flood-drought-flood cycles like we are seeing now in the Midwest, and this sort of weather whiplash is going to be an increasingly severe pain in the neck for society. We'd better prepare for it, by building a more flood-resistant infrastructure and developing more drought-resistant grains, for example. And if we continue to allow heat-trapping gases like carbon dioxide continue to build up in the atmosphere at the current near-record pace, no amount of adaptation can prevent increasingly more violent cases of weather whiplash from being a serious threat to the global economy and the well-being of billions of people.


Video 1. One person was hospitalized after a sinkhole swallowed three cars in the South Deering neighborhood on the Southeast Side of Chicago on Thursday, April 18, 2013. Witnesses said the hole opened up around 5 a.m. at 9600 South Houston Avenue, quickly growing from about 20 feet to about 40 feet. First two cars slid in, then a third as the hole widened, witnesses said. A fourth vehicle was towed from the edge as it was about to fall inside. The sinkhole was due to heavy flooding that broke a water main built in 1915.

Related Science
A 2010 study by Duke University scientists suggests that global warming is the main cause of a significant intensification in the Bermuda High that in recent decades has more than doubled the frequency of abnormally wet or dry summer weather in the Southeast United States. Thus, the Southeast U.S. may see greater than its share of "Weather Whiplash"--extreme droughts followed by extreme floods--in coming decades. Joe Romm at climateporgress.org has a post discussing the paper, with links to examples of how the Southeast U.S. has seen both extreme droughts and extreme floods since 2005.


Jeff Masters

Flood Climate Change Drought

Updated: 7:20 PM GMT on April 19, 2013

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Flash flood emergency in Chicago; dangerous severe weather outbreak possible today

By: JeffMasters, 3:29 PM GMT on April 18, 2013

Torrential downpours from endless thunderstorms fed by an atmospheric river of moisture have pounded the Chicago area since noon Wednesday, forcing declaration of a flash flood emergency in the city this morning. Four to six inches of rain has fallen in the past 24 hours over most of Northern Illinois, with more than half of that total falling since midnight in many areas. Chicago's Ohare Airport received 5.85" as of 10 am CDT, and the 3.84" of rain that has fallen so far today is the heaviest rain ever recorded in a calendar day in the Windy City so early in the year. Radar-estimated rainfall amounts in excess of 8" have occurred in areas of Northwest Illinois about 150 miles east of Chicago. Chicago's all-time 24-hour rainfall record is 9.35", set August 13 - 14, 1987. Another 1 - 2" of rain is likely today in the city. Flooding has been reported in at least 500 basements and homes, and countless roadways are reported under water and impassible. Portions of the Eisenhower, Edens, and Kennedy expressways have been flooded and closed. Several communities have declared a state of emergency, but no injuries have been reported.


Figure 1. Heavy rains in Chicago this morning caused a sinkhole to open up near 96th and Houston streets. The sinkhole was due to a water main break from a pipe constructed in 1915. Image credit: WGN Morning News.


Figure 2. Radar-estimated rainfall amounts in excess of 8" have occurred in areas of Northwest Illinois about 150 miles east of Chicago, and 4 - 6" over most of Northern Illinois.

Chicago flooding a threat to wash Asian Carp into Lake Michigan
The rains have brought the Des Plaines River on the east side of Chicago to major flood stage this morning, and a record flood crest is expected on Friday. The Asian Carp, a dangerous invasive species that would cost billions of dollars were it to get loose in the Great Lakes, is present in the Des Plaines River. Today's flood event is capable of washing significant numbers of Asian Carp from the Des Plaines River into a canal that feeds directly into Lake Michigan, where they might be able to set up a breeding population capable of devastating the Great Lakes' fishing industry. However, in October 2010, the U.S. Army Corps of Engineers completed the Des Plaines River barricade, a 13-mile-long system of concrete barriers and a specially fabricated wire mesh that allows water to flow through the fence but prevents the passage of fish. Hopefully, this barricade will withstand the flood and prevent Asian Carp from washing into Lake Michigan.


Figure 3. The Des Plaines River on the east side of Chicago is at major flood stage, and is expected to crest at record flood levels on Saturday. Image credit: USGS.


Figure 4. The Des Plaines River Asian Carp barrier. Image credit: USACE.

Dangerous severe weather situation for Thursday
NOAA's Storm Prediction Center has placed their "Moderate Risk" forecast of severe weather over an usually large swath of the U.S., from Michigan to Mississippi. A tornado watch issued this morning for most of Indiana and small portions of Eastern Illinois, Southern Lower Michigan, and Northwest Ohio is advising residents that this is "A Particularly Dangerous Situation." NOAA only uses this wording for unusually potent severe weather situations. The risk today is that isolated rotating supercell thunderstorms may develop early this afternoon in advance of a cold front sweeping through the Midwest, and these thunderstorms will bring a moderate risk of EF-2 or stronger tornadoes, hail bigger than golf balls, and wind gusts in excess of 74 mph.


Figure 5. Severe weather outlook for Thursday, April 18, calls for a "Moderate Risk" of severe weather over an usually large swath of the U.S. Large hail, damaging winds, torrential flooding rains, and a few strong EF-2 and EF-3 tornadoes are likely in this region.

Jeff Masters

Flood Severe Weather Yogi

Updated: 12:39 AM GMT on April 19, 2013

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U.S. has a cool and very dry March; severe weather outbreak likely today

By: JeffMasters, 1:08 PM GMT on April 17, 2013

It was another relatively quiet month for weather extremes in the U.S. during March 2013, said NOAA's National Climatic Data Center (NCDC) in their latest State of the Climate report. The month ranked as the 43rd coolest March in the 119-year record for the contiguous U.S., and was the coolest March since 2002. This is in stark contrast to what happened in 2012, when the U.S. had its warmest March on record. Eleven states, mostly in the Southeast, experienced a top-ten coolest March on record in 2013. Remarkably, Florida, Georgia, Alabama, South Carolina, and North Carolina had March 2013 temperatures that were cooler than in January 2013. California, Nevada, and Arizona had a top-ten warmest March. The pattern of warmth in the west and cool conditions in the east was due to the fact that the jet stream was stuck in a large loop that allowed cold air to spill out of Canada into the Southeast U.S., and warm air to flow northward over the southwestern states. We can describe the jet stream behavior using the Arctic Oscillation (AO) Index, which is a measure of pressure patterns across the Arctic. During March 2013, the monthly-averaged AO index reached its most negative March value since records began in 1950.

According to NOAA's U.S. Climate Extremes Index (CEI), which tracks the percentage area of the contiguous U.S. experiencing top-10% and bottom-10% extremes in temperature, precipitation, and drought, the year 2013 has been below average for extremes. The CEI during January - March 2013 was 15%, and on average, about 20% of the contiguous U.S. experiences top-10% extreme weather as defined by the CEI.


Figure 1. Historical temperature ranking for the U.S. for March 2013. Eleven states, mostly in the Southeast, had a top-ten coldest March, and California, Nevada, and Arizona had a top-ten warmest March. Image credit: National Climatic Data Center (NCDC).


Figure 2. Historical precipitation ranking for the U.S. for March 2013. Although only two states had a top-ten driest March--Wyoming and Louisiana--just eight states were wetter than average, making March 2013 the 5th driest March on record for the U.S. as a whole. Image credit: National Climatic Data Center (NCDC).

Fifth driest March on record in the U.S.
Although only two states had a top-ten driest March in 2013--Wyoming and Louisiana--just eight states were wetter than average, making March 2013 the 5th driest March on record for the U.S. as a whole. Thanks to three major winter storms that crossed the Great Plains during the first half of April, there should be a notable improvement in drought conditions over much of the core U.S. drought region when Thursday's Drought Monitor report is issued, though. The most recent report from April 9 showed a big reduction of the area in the worst drought category, "Exceptional", from 5% to 3%, during the first week of April. About 51% of the U.S. is still in moderate or greater drought. According to data from the Rutgers Global Snow Lab, the March snow cover extent for the contiguous U.S. was the 10th largest March snow cover extent in the 47-year period of record. However, snowpack, an important water resource in the West, was below-normal in the Sierra Nevada Mountains as well as the Central and Southern Rockies.


Figure 3. Severe weather outlook for Wednesday, April 17, calls for a "Moderate Risk" of severe weather over much of Oklahoma, and portions of surrounding states. The main threat appears to be large hail, but there may also be a few strong EF-2 and EF-3 tornadoes. You can follow today's severe weather outbreak from our Severe Weather page, and wunderblogger Lee Grenci has a detailed post on today's severe weather threat.

Jeff Masters

Climate Summaries Yogi

Updated: 2:30 PM GMT on April 17, 2013

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NOAA employees may be furloughed 4 days during the 2013 hurricane season

By: JeffMasters, 8:57 PM GMT on April 15, 2013

National Weather Service and NOAA employees may be forced to take up to four unpaid days off this summer, thanks to the the government-wide sequestration cuts which have forced an 8.2% budget cut. NOAA has attempted to respond to the mandatory budget cuts by freezing hiring and cutting back on staff travel and training. However, this has not been enough. In an email sent to all NOAA employees on April 15, Kathryn Sullivan, acting NOAA administrator, said: "We are entering into national consultations with the labor unions that represent some of the NOAA workforce regarding implementation of up to four days of furlough for each NOAA employee before September 30, 2013." The proposed furlough days are July 5, July 19, August 5, and August 30. NOAA employees working at 24/7 operational forecast offices at NWS and the National Hurricane Center would presumably not be furloughed on these days, if there were a major severe weather event occurring. However, I have great concerns that the furlough could cause confusion that would adversely affect critical forecasts and warnings. All of these days fall during hurricane season. The day of greatest concern to me is August 30, which falls during the height of hurricane season (recall that Hurricane Katrina hit the coast on August 29, 2005.) I'm sure that NOAA would do their best to ensure that the furlough would not interfere with critical operations during a landfalling hurricane situation, but would their best be good enough? These are uncharted waters, and its best not to be messing with nation's hurricane warning system during the peak part of hurricane season. In an interview with the Washington Post, Richard Hirn, general counsel for the National Weather Service’s labor union, the National Weather Service Employees Organization, said: “NOAA’s plans to furlough operational employees at the National Weather Service as we enter the severe storm and hurricane season is unnecessary and places the public at great risk." Here is the email sent by Sullivan to NOAA employees today:



Related:
Government budget cuts force leading meteorological training program to seek donations

Sequester may force layoffs of airport weather observers in 109 airports. Some examples: Chattanooga, Lubbock, and West Virginia.

Jeff Masters

Politics

Updated: 8:23 PM GMT on April 16, 2013

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Where's spring? Third winter storm in a week hitting Northern U.S.

By: JeffMasters, 2:52 PM GMT on April 15, 2013

Are we worthy of spring? That's the question residents of much of northern tier of states must be asking themselves this week. The winter of 2012 - 2013 refuses to give way to spring over the Northern Plains and Great Lakes, where snow will once again rule the skies this third week of April. Although the U.S. had an unusually warm winter during 2012 - 2013, ranking as the 20th warmest since 1895, March and the first half of April have been below average in temperature, with March 2013 ranking as the 43rd coldest March in the 119-year record. Two separate April snowstorms have set all time snowiest-day records at two major cities in the Northern Plains, with the latest record to fall the all-time snowiest day for Bismark, North Dakota. On Sunday, Winter Storm Xerxes walloped Bismark with 17.3" of snow, beating the city's previous all-time snowiest day record of 15.5" on March 3, 1966. Sunday's powerful blizzard brought heavy snow, gusty winds of 30 - 40 mph, and near-zero visibility to much of North Dakota, forcing the closure of the entire 350-mile stretch of I-94 through the state on Sunday and Monday morning. Heavy snow and white-out conditions on I-94 in Minnesota closed an additional portion of the freeway in that state, due to a semitrailer crash. Just last week, Winter Storm Walda brought Rapid City, South Dakota its snowiest day on record on April 9, when 20.0" fell at the airport. The 28.2" of snow during April 2013 is now the second snowiest April at the Rapid City Regional Airport, surpassed only by April 1970 when 30.6" of snow fell.


Figure 1. What a difference a year makes: snow was almost non-existent in the Upper Midwest on April 15 last year, but there is plenty this year. Image credit: NOAA.

Spring a slow-show
The cold weather this spring in the Upper Midwest has not been remarkably intense, but it has been unusually persistent, with few breaks from the colder than average conditions. In Fargo, North Dakota, the warmest day so far this year has been 43°F, and the city appears poised to record its latest 50°F on record. According to the NWS in Fargo, the latest day Fargo has hit 50°F was April 17, 1881. The current forecast calls for the temperature to remain below 50° through at least April 24. In Grand Forks, ND, the warmest it has been this year is a chilly 40°F (on January 10.) Spring has also been a slow-show in Michigan's Upper Peninsula, where the 2.3" of snow that fell on Marquette on Sunday brought the seasonal total snowfall over 200"--the first time since the winter of 2007 - 2008 the city has eclipsed that mark. The snow depth in the city is 38", the deepest snow this late in the year since 1980. Marquette's warmest temperature so far this year has been 47°F on March 29. Since Marquette usually records their first 50° reading by March 15, they are a month behind schedule. The latest 50° reading since record keeping began in 1961 was April 26, 1965. The latest forecast calls for the temperature to come close to 50° on Monday, then stay below 50° for the succeeding week, so Marquette may beat its record for latest 50° temperature.

Winter not done with the Upper Midwest yet
Winter isn't done with the region yet--a new slow-moving winter storm called "Yogi" is developing over the Rockies of Northern Colorado. The storm promises to bring up to a foot of snow to Cheyenne, Wyoming, and a swath of 6+ inches to portions Northern Colorado and Nebraska, South Dakota, and Minnesota by Thursday. This storm also has the potential to cause one of the year's largest severe weather outbreaks; NOAA's Storm Prediction Center is already calling for a "Moderate Risk" of severe weather for Oklahoma, Kansas, and Missouri on Wednesday.

Other interesting wunderblogs
It's also been a persistently cold April in Alaska, as weather historian Christopher C. Burt notes in his latest post.

Wunderblogging meteorologist Lee Grenci has an interesting post on why last week's severe weather outbreak had so few tornadoes, despite the presence of a strong cold front and plenty of moisture and thunderstorms.

Jeff Masters

Winter Weather Xerxes Yogi

Updated: 3:18 PM GMT on April 15, 2013

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NOAA report unable to pinpoint causes of the historic 2012 U.S. drought

By: JeffMasters, 7:27 PM GMT on April 12, 2013

The extreme 2012 drought in the Central Great Plains of the U.S. was more intense than any drought since record keeping began in 1895, says a new NOAA assessment of the historic drought, released Thursday. However, the study was unable to pinpoint the cause of the drought. Other major global droughts in recent years have been linked to global warming and/or natural variation in patterns of sea surface temperatures, but these factors were seemingly not important in causing the drought of 2012, said the team of 19 atmospheric scientists, led by Martin Hoerling of the NOAA Modeling, Analysis, Predictions and Projections Program (MAPP). Their study attributed the drought to a random natural variation in the jet stream, which caused it to become "stuck" far to the north in Canada. Since rain-bearing low pressure systems travel along the jet stream, the northwards displacement of the jet stream resulted in abnormally dry conditions over the Central U.S. "This is one of those events that comes along once every couple hundreds of years," said Hoerling.



Key findings of the report
The researchers focused on a six-state region--Wyoming, Kansas, Nebraska, Colorado, Missouri and Iowa, and found that the amount of precipitation in 2012 was only 53% of the long-term average. This was the driest year since record keeping began in 1895, surpassing the previous record driest years of 1934 and 1936, during the great Dust Bowl drought.

The researchers called the 2012 drought a "flash drought"--it developed suddenly in May, and was unrelated to the 2011 drought over Texas and surrounding states. The 2011 drought had a separate and well-understood trigger (a change in the jet stream and storm tracks, due to a La Niña event in the Eastern Pacific.)

The 2012 drought was not predicted by long-range weather forecast models. The new report concluded that our ability to predict drought is limited, but some new experimental techniques could improve future drought forecasts. For example, NOAA's long-range GFDL forecast model and the European EUROSIP model correctly anticipated the summer 2012 heat and dryness over the Central U.S. in projections made as early as January 2012.


Figure 1. Drought-damaged corn in a field near Nickerson, Nebraska, Aug. 16, 2012. The great U.S. drought of 2012 was the most extensive U.S. drought since the 1930s Dust Bowl. Over a six-state region--Wyoming, Kansas, Nebraska, Colorado, Missouri and Iowa--precipitation during 2012 was only 53% of the long-term average., making it the driest year since record keeping began in 1895. Damage from the 2012 drought is at least $35 billion, and probably much higher. The associated heat wave killed 123 people, and brought the U.S. its second hottest summer on record. (AP Photo/Nati Harnik)

Criticism of the report
Dr. Kevin Trenberth of the National Center for Atmospheric Research was critical of the report's conclusions. In comments posted in Joe Romm's blog at climateprogress.org, Dr. Trenberth said that the study failed to "say anything about the observed soil moisture conditions, snow cover, and snow pack during the winter prior to the event in spite of the fact that snow pack was at record low levels in the winter and spring" and "no attempt was made to include soil moisture, snow cover anomalies, or vegetation health" in the climate model runs performed.

I would have liked to have seen the paper mention the growing body of research that has linked unusually early May snow melt in the Northern Hemisphere and Arctic sea ice loss in recent years to unusual summertime jet stream patterns, like the jet stream pattern observed during 2012. A March 2013 paper by scientists at the Potsdam Institute for Climate Impact Research (PIK) in Germany found that under special conditions, the atmosphere can start to resonate like a bell. This causes the jet stream pattern to freeze in place and amplify, leading to months-long periods of weather extremes. They showed that warming of the Arctic due to human-caused climate change might be responsible for this resonance phenomenon, which became twice as common during 2001 - 2012 compared to the previous 22 years. One of the more extreme examples of this resonance occurred during the summer of 2012, and could have been the cause of the 2012 drought.

Other blogs on the report
Yes, Climate Change Is Worsening U.S. Drought — NOAA Report Needlessly Confuses The Issue by Joe Romm at climateprogress.org

Global Warming Not Significant in 2012 Drought: Report by Andrew Freedman of climatecentral.org

Have a great weekend, everyone!

Jeff Masters

Drought Climate Change

Updated: 4:47 PM GMT on April 13, 2013

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Tornado kills one in Mississippi, but a quiet spring for tornadoes so far

By: JeffMasters, 3:12 PM GMT on April 12, 2013

Tornadoes ripped through the U.S. on Thursday for the fourth day this week, as a slow-moving spring storm brought a variety of major weather extremes across the nation. Seven preliminary tornadoes were recorded on Thursday, and one person was killed by a tornado that hit Liberty, Mississippi. Multiple injuries were reported from a tornado that hit Shuqualak, Mississippi. The strongest verified tornadoes so far from this week's outbreak were EF-2 tornadoes that hit Hazelwood, Missouri and Botkinburg, Arkansas on Wednesday, April 9.


Figure 1. A tornado roars through Noxubee County, Mississippi on Thursday, April 11, 2013. Check out this impressive video posted to Facebook of the tornado. This is probably the same tornado that killed one person near Liberty, MS.


Figure 2. Doppler velocity image of the tornado that hit Liberty, MS on April 11, 2013. The characteristic pattern of red and green colors right next to each other, showing winds moving both towards and away from the radar, show the presence of a rotating thunderstorm just north of De Kalb, MS in this image.

A quiet 2013 tornado season so far
Thursday's tornado death brought this year's tornado death toll to three, which is well below average for this time of year. According to NOAA's Storm Prediction Center, during January - March 2012, the U.S. had 60 tornado deaths. The preliminary tally for April tornadoes is 23, which is also well below average for the first eleven days of April. During the previous three years, 2010 - 2012, the U.S. averaged 368 tornadoes during the month of April. The quiet April for tornadoes follows a very quiet March; the preliminary March tornado tally of eighteen is the lowest for any March since 1978. The latest 10-year March average U.S. tornadoes through 2012 is 98. Here are the March tornado tallies below twenty tornadoes since 1950:

18: 2013
17:  1978
8:  1969
12:  1966
15:  1958
6:  1951

The reason for the low tornado numbers this spring is the unusually cool conditions that have kept instability levels low over the eastern two-thirds of the country. This has been due to a negative phase of the Arctic Oscillation (AO), which has kept a southwards-bulging portion of the jet stream in place over the eastern portion of the U.S., allowing cool air from Canada to spill southwards. NOAA's Storm Prediction Center does not have any risk areas for severe weather delineated through Sunday, but another major storm system is expected to develop over the Midwest on Tuesday, which will likely bring additional severe weather.

Jeff Masters

Tornado

Updated: 6:46 PM GMT on April 12, 2013

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Hurricane Sandy's name retired; Isaac snubbed

By: JeffMasters, 6:24 PM GMT on April 11, 2013

Hurricane Sandy has been permanently retired from the list of Atlantic hurricane names, NOAA announced today. Sandy was by far the deadliest and most destructive Atlantic tropical cyclone of 2012, with damages estimated at $50 billion. Sandy killed at least 147 people across the Atlantic basin, including 72 in the mid-Atlantic and northeastern United States--the highest U.S. hurricane death toll outside of the southern states since Hurricane Agnes of 1972. Sandy is the 77th name to be retired in the Atlantic since hurricanes began getting names in 1953. Sandy is the second name beginning in "S" to get retired, joining 2005's Hurricane Stan. The only letter of the alphabet used to name hurricanes that hasn't had a storm beginning with that letter retired is "V". Hurricane names are recycled every six years, and the name Sandy will be replaced by "Sara" beginning in 2018. In a bit of a surprise, the World Meteorological Organization committee in charge of retiring hurricane names elected not to retire Hurricane Isaac. Isaac only reached Category 1 strength, but killed 34 people: 24 in Haiti, 5 in the Dominican Republic, and 5 in the U.S. The hurricane drove a storm tide up to seventeen feet high into Louisiana, and caused $2.35 billion in U.S. damage.


Figure 1. Hurricane Sandy two hours before landfall in New Jersey on October 29, 2012. Image credit: NOAA.

Portlight receives $250,000 grant for Hurricane Sandy relief efforts
On September 14, 2008, the devastation wrought by Hurricane Ike on Texas and Louisiana moved members of the wunderground community to put into action their own impromptu relief effort. From this humble beginning has grown a disaster-relief charity I have been proud to support--Portlight.org. Since 2008, Portlight has responded to numerous disasters with the aim of helping the underserved, unserved, and forgotten people. Portlight's strong showing in the wake of Hurricane Sandy has gotten them some major recognition. On April 4, the Hurricane Sandy New Jersey Relief Fund announced that Portlight would receive $250,000 to assist disabled people living in Monmouth, Ocean, Middlesex, Atlantic, and Cape May Counties in New Jersey. The money will be used for wheelchair ramp replacement and construction, replacing durable medical equipment, and providing accessibility for raised homes in line with ADA requirements to ensure those with disabilities can remain in their homes. "Those with disabilities have been historically underserved in times of disaster, and could be permanently forced out of their homes without proper access, particularly if homes are raised based on new building guidelines. For those who are forced out, finding accessible, affordable housing can be an even greater challenge," said Paul Timmons, Chair of Portlight Strategies, Inc. "This funding is an enormous gift which will help construct wheelchair ramps, vertical lifts and replace medical equipment so those with disabilities can remain independent and stay in their homes." Please visit the Portlight.org web site or the Portlight blog to learn more and donate.


Figure 2. Portlight volunteers hard at work in New Jersey, cleaning up after Hurricane Sandy in March, 2013. Image credit: Paul Timmons.

Jeff Masters

Hurricane

Updated: 11:44 AM GMT on April 12, 2013

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Active 2013 Atlantic Hurricane Season Expected by CSU, TSR, and WSI

By: JeffMasters, 4:02 PM GMT on April 10, 2013

After three consecutive years with a remarkable 19 named storms in the Atlantic, expect another Atlantic hurricane season with similar levels of activity in 2013, says the hurricane forecasting team of Dr. Phil Klotzbach and Dr. Bill Gray of Colorado State University (CSU) in their latest seasonal forecast issued April 10. They call for an Atlantic hurricane season with 18 named storms, 9 hurricanes, 4 intense hurricanes, and an Accumulated Cyclone Energy (ACE) of 165. The long-term averages for the past 63 years are 11 named storms, 6 hurricanes, 3 intense hurricanes, and an ACE of 103. The active hurricane period that began in 1995 has averaged 15 named storms, 8 hurricanes, and 4 major hurricanes. The 2013 forecast calls for an above-average chance of a major hurricane hitting the U.S., both along the East Coast (48% chance, 31% chance is average) and the Gulf Coast (47% chance, 30% chance is average). The Caribbean is forecast to have a 61% chance of seeing at least one major hurricane (42% is average.) Five years with similar pre-season February and March atmospheric and oceanic conditions were selected as "analogue" years that the 2013 hurricane season may resemble: 2004 (which featured seven major hurricanes, including four that hit the U.S.); 1996 (six major hurricanes, including Cat 3 Hurricane Fran that hit North Carolina); 1966 (three major hurricanes, featuring Cat 4 Inez, which hit Mexico, Hispaniola, Cuba, the Bahamas, and Florida); 1952 (only seven named storms, but three major hurricanes); and 1915, which boasted a Cat 3 hurricane that hit New Orleans and a Cat 4 that hit Galveston. These years all had neutral El Niño conditions, above-average Sea Surface Temperatures (SSTs) in the tropical and North Atlantic, and cool ocean temperatures in the Northeast Pacific (a negative PDO) during February - March. None of the five analogue years had a significant El Niño during the peak of the hurricane season. The average activity for these years was 10 named storms, 7 hurricanes, and 4 major hurricanes.


Figure 1. Hurricane Michael as seen by NASA's Aqua satellite at 12:20 pm EDT Thursday September 6, 2012. At the time, Michael was a major Category 3 hurricane with 115 mph winds. Hurricane Sandy was the only other major Atlantic hurricane of 2012. Image credit: NASA.

Why the forecast of an active season?
The CSU team cited two main reasons why this may be an active hurricane season:

1) Neutral El Niño conditions are expected during the August - September - October peak of hurricane season. Since the active hurricane period we are in began in 1995, neutral years have seen much above-average activity (remember the neutral El Niño year of 2005?) If El Niño conditions are present this fall, this will likely bring about a quiet Atlantic hurricane season due to increased upper-level winds over the tropical Atlantic creating wind shear that will tend to tear storms apart.

2) Sea surface temperatures (SSTs) in the Main Development Region (MDR) for hurricanes from the Caribbean to the coast of Africa between 10°N and 20°N were near-average in the western tropical Atlantic, but unusually warm in the eastern tropical Atlantic, in March 2013. Much of this unusual warming was due to a persistent negative phase of the North Atlantic Oscillation (NAO) since mid-February (which also brought an unusually cold March to the Eastern U.S. and Western Europe.) A negative phase of the NAO is associated with a weakened Bermuda-Azores High and slower trade winds across the tropical Atlantic. The slower winds allow the ocean to heat up more, due to less mixing of cool water to the surface. Virtually all African tropical waves originate in the MDR, and these tropical waves account for 85% of all Atlantic major hurricanes and 60% of all named storms. When SSTs in the MDR are much above average during hurricane season, a very active season typically results (if there is no El Niño event present.) Conversely, when MDR SSTs are cooler than average, a below-average Atlantic hurricane season is more likely.


Figure 2. Departure of sea surface temperature (SST) from average for April 8, 2013, as computed by NOAA's NESDIS branch. SSTs in the hurricane Main Development Region between Africa and Central America (red box) were well above-average.

How good are the April forecasts?
The forecasters are using a statistical model developed in 2011 for making April forecasts, so we don't have a long enough track record to judge how good the new model is. The new model predicted a below-average year for 2012, with 10 named storms, 4 hurricanes, and 2 intense hurricanes. The actual tally was much higher, with 19 named storms, 10 hurricanes, and 2 intense hurricanes. April forecasts of hurricane season activity are low-skill, since they must deal with the so-called "predictability barrier." April is the time of year when the El Niño/La Niña phenomenon commonly undergoes a rapid change from one state to another, making it difficult to predict whether we will have El Niño, La Niña, or neutral conditions in place for the coming hurricane season. Correctly predicting this is key, since if El Niño conditions are present this fall, this will likely bring about a quiet Atlantic hurricane season due to increased upper-level winds over the tropical Atlantic creating wind shear that will tend to tear storms apart. Currently, ocean temperatures are very close to average in the Eastern Pacific, and the large majority of the El Niño models are predicting a continuation of these neutral conditions for the coming hurricane season.

CSU maintains an Excel spreadsheet of their forecast errors ( expressed as a mathematical correlation coefficient, where positive means a skilled forecast, and negative means they did worse than climatology) for their their April forecasts. For now, these April forecasts should simply be viewed as an interesting research effort that has the potential to make skillful forecasts. The next CSU forecast, due on Monday, June 3, is the one worth paying attention to. Their early June forecasts have shown considerable skill over the years.

TSR predicts an active hurricane season
The April 5 forecast for the 2013 Atlantic hurricane season made by British private forecasting firm Tropical Storm Risk, Inc. (TSR) calls for an active season with 15 named storms, 8 hurricanes, 3 intense hurricanes, and an Accumulated Cyclone Energy (ACE) of 131. The long-term averages for the past 63 years are 11 named storms, 6 hurricanes, 3 intense hurricanes, and an ACE of 103. TSR rates their skill level as low for these April forecasts--just 6 - 15% higher than a "no-skill" forecast made using climatology. TSR predicts a 63% chance that U.S. land falling activity will be above average, a 21% chance it will be near average, and a 16% chance it will be below average. They project that 4.4 named storms will hit the U.S., with 1.9 of these being hurricanes. The averages from the 1950-2012 climatology are 3.1 named storms and 1.4 hurricanes. They rate their skill at making these April forecasts for U.S. landfalls just 7 - 8% higher than a "no-skill" forecast made using climatology. In the Lesser Antilles Islands of the Caribbean, TSR projects 1.5 named storms, 0.6 of these being hurricanes. Climatology is 1.1 named storms and 0.5 hurricanes.

TSR’s two predictors for their statistical model are the forecast July - September trade wind speed over the Caribbean and tropical North Atlantic, and the forecast August - September 2013 sea surface temperatures in the tropical North Atlantic. Their model is calling for warmer than average SSTs and slower than average trade winds during these periods, and both of these factors should act to increase hurricane and tropical storm activity.

WSI predicts an active hurricane season
The April 8 forecast from the private weather firm WSI (part of The Weather Company, along with The Weather Channel, Weather Central, and The Weather Underground), is calling for an active season with 16 named storms, 9 hurricanes, and 5 intense hurricanes.



Jeff Masters

Hurricane

Updated: 5:10 PM GMT on April 10, 2013

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One-inch hail at 18°F in NE; record snows in SD

By: JeffMasters, 1:54 PM GMT on April 10, 2013

It's crazy spring weather at its finest in the Midwest U.S., where a powerful April storm system is bringing heavy snow, large hail, strong winds, freezing rain, heavy rain, and a remarkable temperature contrast on either side of its cold front. Abilene, Texas reached 93° Tuesday between 4 - 5 pm, and by 12:30 a.m Wednesday, it was snowing and 37°. Texas had an extreme temperature range state-wide on Tuesday of at least 86°: from 108° in Laredo, to 22° in Dalhart. A damaging hail storm moved though the west side of Omaha, Nebraska on Tuesday night, bringing hail up to 2" inches in diameter with damage to cars, skylights, roofs and windshields, according to the Omaha World-Herald. The Grand Island, NE airport had hail up to nickel size while the temperature was 27°F, and one location nearby had 1" sized hail with a surface temperature of just 18°F. It is very rare to see large hail with surface temperatures this cold; the unusual weather was made possible by elevated thunderstorms along a front aloft, above a shallow surface-based cold layer. Wunderground weather historian Christopher C. Burt has a post, Incredible Temperature Gradient in Southern/Central Plains, discussing the remarkable contrast between the weather on either side of the cold front. NOAA's Storm Prediction Center is predicting a "Slight" chance of severe weather today through Friday along the storm's cold front, as it sweeps eastwards towards the East Coast.

A remarkable 20" of snow piled up in Rapid City, SD on Tuesday--the city's snowiest day of all-time. The previous one-day record was 18", set on April 22, 2001. The snow continues to fall in the city, with a storm-total accumulation of 25" as of 8 am CDT. The storm has knocked out power to thousands in the Sioux Fall, SD area, and I-90 is closed between Rapid City and Mitchell this morning. However, the Rapid City area is under the highest level of drought, exceptional, so the record snow storm is not entirely unwelcome. Widespread areas of one to two inches of precipitation have fallen over some of the hardest-hit drought areas of South Dakota, Oklahoma, and Nebraska this week, making the week one of the biggest for Midwest drought reduction experienced in the past year.

I'll have a new post late this morning on the latest hurricane season forecasts.

Jeff Masters

Severe Weather Winter Weather Walda

Updated: 1:55 PM GMT on April 10, 2013

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Europe expected to see a large increase in Hurricane Sandy-like hybrid storms

By: JeffMasters, 4:18 PM GMT on April 08, 2013

Watch out, Europe. Dangerous part-hurricane, part extratropical hybrid storms like Hurricane Sandy of 2012 are expected to be an increasing threat for Western Europe by the end of the century due to global warming, said a team of scientists led by Reindert J. Haarsma of the Royal Netherlands Meteorological Institute. In a paper called "More hurricanes to hit Western Europe due to global warming", published in April 2013 in Geophysical Research Letters, the researchers describe the results from runs of a high-resolution (25 km grid spacing) climate model based on the European Centre for Medium Range Weather Forecasts (ECMWF) numerical weather prediction model. The model predicts that the breeding ground for Atlantic hurricanes will shift approximately 700 miles eastwards as the oceans warm this century. Hurricanes which form farther to the east can spend more time over warm tropical waters before turning north and northeast towards Europe, increasing the odds that these storms will have hurricane-force winds upon arrival in Europe. The model showed that wind shear will change little in the region over the coming decades, resulting in a large increase in storms with hurricane-force winds affecting Western Europe. Most of the these storms will not be tropical hurricanes upon arrival in Europe, but will be former hurricanes that have transitioned to extratropical storms. However, as we saw with Hurricane Sandy of 2012, these hybrid storms can be extremely dangerous. Summed over Norway, the North Sea, and the Gulf of Biscay, the model found that the number of hurricane-force storms in August - October increased from 2 to 13 over the 21st century, with almost all future West European hurricane-force storms predicted to originate as hurricanes or tropical storms in the tropics by 2100. The researchers conclude that "tropical cyclones will increase the probability of present-day extreme events over the North Sea and the Gulf of Biscay with a factor of 5 and 25 respectively, with far reaching consequences especially for coastal safety."


Figure 1. Hurricane Sandy at 10:10 am EDT October 28, 2012. Image credit: NASA/GSFC.

Europe's hurricane history
Only once since accurate records began in 1851 has an actual hurricane with full tropical characteristics hit Europe. This happened on September 16, 1961, when Category 1 Hurricane Debbie hit northwestern Ireland. Wind gusts reached 106 mph at Ballykelly and 104 mph at Tiree and Snaefill, and coastal radio stations reported the airwaves were jammed with calls for help from small ships and fishing craft. Eleven people were killed and 50 injured in the storm. The only other tropical cyclone recorded to have hit Europe since 1851 was Hurricane Vince of 2005, which hit southern Spain as a tropical depression on October 11, 2005. Historical documents also suggest a hurricane hit Spain on October 29, 1842.


Figure 2. Hurricane Debbie of 1961 was the only fully tropical hurricane ever recorded to hit Europe.

Britain's history of ex-hurricane strikes
Hurricanes that transition to powerful extratropical storms hit the British Isles several times per decade, on average. In October 2014, after battering Bermuda, the remnants of Hurricane Gonzalo affected Europe as a powerful extratropical storm, bringing strong winds, torrential rain, and heavy snowfall in western, central, and southern portions of the continent. Three people were killed, and damages in Netherlands, Germany, and Slovenia were estimated at $42 million. In 2011, Hurricane Katia brushed by Newfoundland, made the transition from a tropical system to a powerful extratropical storm, and maintained strong winds of 50 - 65 mph as it crossed the Atlantic. Ex-Katia hit northern Scotland on September 12, 2011. Glen Ogle, Scotland, at an elevation of 1500 feet (546 meters), received sustained winds of 60 mph, gusting to 86 mph. Cairngorm, in the Scottish Highlands at an elevation of 4085 feet, reported sustained winds of 67 mph. With the trees in full leaf, tree damage was much higher than a winter or springtime storm of similar ferocity would have caused. One person was killed by a falling tree, and heavy tree damage and numerous power failures were reported throughout Britain. Other gusts experienced in Britain included 76 mph at Edinburgh Blackford Hill, 75 mph at Capel Curig in Wales, 72 mph at Glasgow Bishopton, and 71 mph at Loftus, North Yorkshire.


Figure 3. Image of Hurricane Katia taken from the International Space Station at 15 GMT September 9, 2011, by astronaut Ron Garan. At the time, Katia was a Category 1 hurricane with 85 mph winds. Long Island, New York is visible at the lower left.


Figure 4. Surface wind estimate from the Windsat satellite at 4:04 am EDT on Monday, September 12, 2011. The center of Extratropical Storm Katia is marked by an "L", and winds in excess of 50 knots (58 mph, purple triangles) were occurring to the southwest of the center, near the west coast of Ireland. Image credit: NOAA.

As reported by UK Met Office forecaster John Hammond in a post on the BBC 23 degrees blog, Britain has been affected at least eight times in the past twenty years by extratropical storms that were once tropical storms or hurricanes. Before Katia of 2011, the most recent such storm was Hurricane Bill of 2009, which hit Ireland as an extratropical storm on August 25 with sustained winds of 45 mph. Bill was a Category 4 hurricane northeast of the Lesser Antilles five days prior. In 2006, a record three extratropical storms that had once been tropical cyclones hit Britain:

Extratropical Storm Alberto, which had been a strong tropical storm that hit the Florida Panhandle, hit northern Ireland and Scotland as an extratropical storm with 35 mph winds.

Extratropical Storm Gordon hit Ireland on September 21, 2006, with sustained winds of 65 mph. Gordon brought record warm temperatures as tropical air pushed north across the UK, and also strong winds that brought down power lines in Northern Ireland. Wind gusts to 60 mph (97 km/h) occurred in the Isles of Scilly off the southwest coast, and 81 mph (130 km/h) on the mainland.

Extratropical Storm Helene hit Northwestern Ireland on September 27, 2006, with sustained winds of 45 mph.

Figure 5. Path of Hurricane Lili of 1996, which caused $420 million in damage to the U.K. as an extratropical storm.

Other post-tropical cyclones that have the U.K. in the past twenty years include Hurricanes Isaac and Leslie of 2000, Hurricane Karl of 1998, and Hurricane Lili of 1996. The most severe of these storms was Extratropical Storm Lili, which hit Ireland on October 28, 1996, with sustained winds of 65 mph. Lili caused $420 million in damage (2011 dollars) in the U.K. According to Wikipedia, Lili produced a 92 mph (148 km/h) gust at Swansea, South Wales, while bringing a 4' (1.2 meter) storm surge that inundated the River Thames. In Somerset, 500 holiday cottages were severely damaged. A U.S. oil drilling platform, under tow in the North Sea, broke loose during the storm and nearly ran aground at Peterhead. On the Isle of Wight, a sailing boat was beached at Chale Bay; luckily all five occupants were rescued. It was the most damaging storm to have struck the United Kingdom since the Great Storm of 1987, which killed 22 and did $660 million in damage (1996 dollars.) However, Lili also broke a four-month drought over southwest England.

All but one of these storms hit during the peak part of hurricane season, mid-August - late October. The only exception was Ex-Tropical Storm Alberto of 2006, which hit Britain in June.


Figure 6. Hybrid subtropical storm of October 8, 1996, off the coast of Italy. According to Reale and Atlas (2001), the storm had characteristics similar to a hurricane, but formed over cool waters of 21.5°C (71°F.) They reported that "The maximum damage due to wind occurred over the Aeolian Islands, at 38.5°N, 15°E, to the northeast of Sicily: assistance for disaster relief was required. Unfortunately, no weather station data were available, but the media reported sheds, roofs and harbor devices destroyed, and houses and electric lines damaged, due to 'extremely strong westerly wind.' The perfect agreement between the observations at Ustica, the storm scale, the eye-like feature position and the damages over the Aeolian Island reasonably suggest that the hurricane-level intensity of 32 m/s (72 mph) was reached over the Aeolian Islands." A similar hybrid low affected Algeria on 9 - 10 November 2001. This storm produced upwards of 270 mm (10.6") of rain, winds of 33 m/s (74 mph), and killed 737 people near Algiers, mostly from flooding and mud slides. Image credit: Dundee satellite receiving station.

Hurricanes in the Mediterranean Sea?
The Mediterranean Sea between Europe and Africa has experienced several damaging hybrid subtropical storms in recent decades, but has never experienced a fully tropical hurricane in recorded history. However, global warming may cause the Mediterranean to start spawning hurricanes by 2100, according to a 2007 study by a research team led by Miguel Angel Gaertner of the University of Castilla-La Mancha in Toledo, Spain. They ran nine different climate models with resolutions of about 50 km and found that some (but not all) of the models simulated hurricanes in the Mediterranean in September by the end of the century, when ocean temperature could increase by 3°C, reaching 30°C.

Though the Mediterranean may start seeing hurricanes by the end of the century, these storms should be rare and relatively short-lived for three reasons:

1) The Mediterranean is quite far north and is subject to strong wind shear from jet stream activity.

2) The waters are shallow, and have relatively low heat content. There is no deep warm water current like the Gulf Stream.

3) The Mediterranean has a lot of large islands and peninsulas poking into it, increasing the chances that a tropical storm would weaken when it encountered land.

References
Gaertner, M. A., D. Jacob, V. Gil, M. Dominguez, E. Padorno, E. Sanchez, and M. Castro (2007), Tropical cyclones over the Mediterranean Sea in climate change simulations, Geophys. Res. Lett., 34, L14711, doi:10.1029/2007GL029977.

Haarsma et al., 2013, More hurricanes to hit Western Europe due to global warming, Geophysical Research Letters, DOI: 10.1002/grl.50360

Reale, O., and R. Atlas. 2001: Tropical Cyclone-Like Vortices in the Extratropics: Observational Evidence and Synoptic Analysis, Weather and Forecasting, 16, No. 1, pp. 7-34.

Jeff Masters

Hurricane Climate Change

Updated: 11:33 PM GMT on November 05, 2014

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Damaging Winds Rip Cruise Ship from Its Moorings

By: Lee Grenci , 12:30 PM GMT on April 05, 2013

In the early afternoon on Wednesday, April 3, 2013, fierce winds ripped the cruise ship, Triumph, from its moorings along the Mobile River (Mobile, Alabama). Check out the AP photograph below. Damaging winds had occurred around noon near New Orleans, Louisiana, shifting east-northeastward toward Gulfport, Mississippi, and Mobile. Curiously, the Storm Prediction Center didn't show any storm reports of damaging winds for April 3. That's because damaging winds were, technically speaking, "non-thunderstorm" winds.



A close-up photograph of some of the damage incurred to the cruise ship, Triumph, after fierce winds caused the ship to break loose from its moorings in the early afternoon of April 3, 2013. Courtesy of the Associated Press.

Yet these fierce winds were related to the mesoscale convective system (MCS) that moved across the Gulf Coast States on Wednesday (check out the 17Z mosaic of composite reflectivity). For starters, a mesoscale convective system is any meso-beta (20 to 200 kilometers) or meso-alpha (200 to 1000 kilometers) group of thunderstorms that are part of a contiguous area of convective and straitform rains that span 100 kilometers or more in at least one horizontal direction. This sequence of images of radar reflectivity displays some of the various kinds of precipitation structures associated with mesoscale convective systems (courtesy of UCAR and The Comet Program).



The 14Z Rapid Refresh model analysis of mean sea-level isobars (drawn every two millibars) and surface winds on April 3, 2013. The Rapid Refresh data were superimposed on base reflectivity. Note the wake low in the "wake" of the mesoscale convective system. Courtesy of the Storm Prediction Center.

Early on April 3, a mesoscale area of low pressure, formally called a wake low, followed in the "wake" of the mesoscale convective system. To see what I mean, check out the 14Z Rapid Refresh model analysis of mean sea-level isobars (drawn every two millibars) and surface winds superimposed on the 14Z base radar reflectivity (above). I annotated the image for you to see the position of the wake low relative to the MCS.


A wake low forms when subsiding air in the wake of the MCS warms on descent. In a nutshell, this compressional warming increases the mean temperature in columns of air that extend from the earth's surface to high in the stratosphere. This increase in mean column temperature decreases the mean column air density, which, in turn, lowers the weight of the air columns and the surface pressure (when the atmosphere is nearly hydrostatic, the weight of air columns from the earth's surface to near the top of the atmosphere serves as a proxy for surface air pressure).



The 17Z mosaic of composite reflectivity on April 3, 2013. Note the tongue of dry air eroding the stratiform rain on the backside of the MCS. Courtesy of Penn State.

If we look more closely at the 17Z mosaic of composite reflectivity (above), it appears that there was a tongue of very dry air "cutting into" the trailing stratiform shield of precipitation on the backside of the mesoscale convective system. To get a better sense for how this mid-level very dry air literally charged into the wake of the MCS, check out this 10-hour loop of radar reflectivities (takes a moment to load; courtesy of SPC) that span from 0935Z to 1935Z. The dark region on the 17Z water vapor image from GOES-13 confirms the notion of intruding dry, mid-level air. At any rate, seasoned forecasters recognize this "charge" of very dry mid-level air as a precursor for high-wind episodes associated with wake lows. So I'm really suggesting that nowcasting this event would fall into the category of pattern recognition.


When a tongue of very dry mid-level air originating over the high deserts of the Southwest "charges" eastward and intrudes beneath the anvil cloud of a mesoscale convective system, precipitation falling from the anvil of the MCS completely evaporates. Now subsiding air dramatically warms at the DALR (dry adiabatic lapse rate), markedly increasing the mean temperature in air columns and lowering air densities, column weights and, ultimately, surface pressure. If the layer of intruding dry air is sufficiently deep and surges eastward in the vicinity of the wake low, there can be rapid and dramatic hydrostatic pressure falls at the earth's surface, paving the way for strong surface winds.



The 17Z Rapid Refresh model analysis of mean sea-level isobars and surface winds on April 3, 2013. The red "L" and the blur "H" indicate, respectively, the wake low and mesohigh associated with rain-cooled air. Courtesy of SPC.

Let's look more closely at the mesoscale weather pattern around midday. Check out, above, the 17Z Rapid Refresh model analysis of mean sea-level isobars, surface winds and base reflectivity. Remember that isobars are drawn every two millibars, so the pressure gradient between the wake low (the red "L") and the mesohigh associated with relatively dense, rain-cooled air (the blue "H") looks a bit larger than it actually was. Certainly, the winds generated by this rather modest pressure gradient were not strong enough to move a cruise ship off its moorings. No, there was something else going on.


Take a look (below) at the 19Z Rapid Refresh model analysis of 2-hour pressure tendency (dashed blue contours represent pressure falls, expressed in millibars per two hours). If you look closely, you'll observe an isallobar labeled minus five millibars per two hours (between 17Z and 19Z) in the vicinity of the wake low, indicating the dramatic impact on surface pressure caused by the eastward "charging" mid-level dry air that I discussed earlier. In contrast, there were only modest positive pressure tendencies associated with the mesohigh during these two hours.



The 19Z Rapid Refresh model analysis of 2-hour pressure tendencies on April 3, 2013. Dashed, blue contours indicate negative pressure tendencies (pressure decreased during the two-hour period from 17Z to 19Z). Courtesy of SPC.

Nonetheless, the pocket of negative pressure tendencies in the vicinity of the rapidly intensifying wake low promoted strong isallobaric acceleration toward the west, helping to generate damaging, "non-thunderstorm" winds. For the record, the isallobaric wind is an ageostrophic component of the wind that arises from changes in pressure over time. In general terms, it blows from a pocket of positive pressure tendencies toward a pocket of negative pressure tendencies (check out this example of the isallobaric wind component...contours are isallobars representing surface pressure changes over a period of three hours).


Quite an event, wouldn't you agree?


Lee

Recent News Mesoscale Forecasting

Updated: 12:31 PM GMT on April 08, 2013

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Severe Weather and Mesoscale Boundaries

By: Lee Grenci , 11:21 AM GMT on April 02, 2013

Featured wunderblogger Lee Grenci will be filling in for me this week while I'm on vacation. I'll be back to blogging on Monday.

- Jeff Masters


I often categorize cold fronts, warm fronts, stationary fronts, etc. as synoptic-scale features, but, when I do, I mean the along-front scale, which can extend a thousand kilometers or more. The cross-front scale, however, is often only 100 kilometers or less, rendering any circulation a mesoscale phenomenon. In my view (the definition of mesoscale is somewhat subjective), the mesoscale spans from 2 to 1000 kilometers, with the meso-gamma scale extending from 2 to 20 kilometers (a large tornado or the rotating updraft of a supercell thunderstorm), the meso-beta scale covering 20 to 200 kilometers (a relatively small mesoscale convective system), and the meso-alpha scale, spanning from 200 to 1000 kilometers (most tropical cyclones fall into this category).



My subjective subdivisions of the mesoscale (2-1000 kilometers). The photograph insets on the left are meant to provide readers with example mesoscale weather features that represent each subdivision. Courtesy of Penn State's online certificate program.

Seasoned forecasters who predict severe weather are always aware of synoptic-scale fronts and dry lines (a topic for another day) as boundaries between contrasting air masses than can initiate deep, moist convection, which is a more technical term for thunderstorms. By "initiate," I mean lifting air parcels to the level of free convection (LFC), the altitude at which parcels become warmer than their environment and accelerate upward in response to this temperature difference. In other words, air parcels are positively buoyant through a deep layer of the troposphere (between the LFC and the equilibrium level). For the record, the equilibrium level (EL) is the altitude where the temperature of the rising parcel once again equals the temperature of its environment. Technically speaking, upward-accelerating air parcels overshoot the equilibrium level because they can't just stop on a dime (I highly recommend this instructive flash animation, courtesy of UCAR and The Comet Program).


In addition to synoptic-scale fronts and boundaries as possible initiation sites for thunderstorms, forecasters must also identify much more subtle mesoscale boundaries that can also lift air parcels to the level of free convection and initiate deep, moist convection. When I say "mesoscale" here, I'm referring to the along-front dimension, so the contrasting air masses separated by the mesoscale boundary are relatively small compared to their synoptic-scale cousins. Examples of mesoscale boundaries include gust and sea-breeze fronts. A gust front is the leading edge of rain-cooled air associated with the splashdown of thunderstorm downdrafts, and a sea-breeze front is the leading edge of maritime air moving inland as a result of the uneven heating of land and coastal waters (another future blog topic for Lee). In more general terms, mesoscale boundaries typically form in response to the uneven heating of the earth's surface (sea-breeze fronts, for example) or in concert with a relatively large horizontal gradient in latent heating / latent cooling (gust fronts, for example).



The graphic for Mesoscale Convective Discussion #342 issued by the Storm Prediction Center at 2153Z on March 30, 2013 (4:53 P.M. CDT). Courtesy of SPC.

At 4:53 P.M. CDT on Saturday, March 30, 2013, the Storm Prediction Center issued Mesoscale Discussion #342 (see graphic above), identifying mesoscale boundaries over the panhandle of Texas and a portion of Oklahoma as pretty safe bets to initiate thunderstorms that had the potential to produce severe weather (purpose of mesoscale discussions). The dashed, brown lines on the SPC graphic for MD #342 indicated the mesoscale boundaries (full text for MD #342). By the way, "342" refers to the running count of mesoscale discussions for the year.

During the daytime hours, forecasters often identify mesoscale boundaries using high-resolution visible satellite imagery. For this case, I annotated this 2145Z visible image from GOES-13 in order to highlight portions of the two mesoscale boundaries. To get a better sense for why I used the word, "subtle" in the context of mesoscale boundaries, check out this unannotated version. Here's an annotated close-up of the 2145Z visible image showing portions of the mesoscale boundaries over the panhandle of Texas and portions of Oklahoma.



The 2145Z visible satellite image from GOES-13 on March 30, 2013. Can you find two mesoscale boundaries over the panhandle of Texas and portions of Oklahoma? Here's the answer. Courtesy of NOAA and Penn State.

About one hour later, deep, moist convection erupted along segments of the mesoscale boundaries (see the 2245Z visible image below). I circled the discrete thunderstorms in yellow. Farther south, you'll see more thunderstorms initiated by the dry line. I'll include the 21Z surface analysis so you can get a better sense for the position of the dry line around this time (late Saturday afternoon). Note how the storm anvils (photographs) spread toward the southeast in tandem with northwesterly upper-level winds (here's the GFS model analysis of 300-mb streamlines at 18Z on March 30; the standard height of 300 mb is 9000 meters, which is roughly 30,000 feet).



The 2245Z visible image from GOES-13 on March 30, 2013. The yellow circle encompasses thunderstorms that were initiated along two mesoscale boundaries over the Texas Panhandle and portions of Oklahoma.

As the warm season unfolds, I'll post blogs on mesoscale meteorology and forecasting. In the final analysis, "becoming one with the atmosphere" is the key philosophy for successfully predicting thunderstorms. The positions of synoptic-scale fronts and upper-level disturbances provide forecasters with the "big picture," but discovering subtle mesoscale boundaries can sometimes make a general thunderstorm forecast much more precise (with regard to location and timing).


Lee

Mesoscale Meteorology Mesoscale Forecasting

Updated: 2:59 PM GMT on April 02, 2013

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Invisible Improbable Rain Discovered!

By: JeffMasters, 2:15 AM GMT on April 01, 2013

A stunning discovery by a humble Weather Underground personal weather station owner has rocked the meteorological world. Boris Badi-i-sad-o-bist-roz, who maintains a backyard weather station in Watrousville, Michigan, has discovered the existence of improbable rain, which promises to revolutionize the understanding and prediction of the weather. In an interview, Mr. Badi-i-sad-o-bist-roz described his improbable discovery of improbable rain. "I was in my backyard, sticking a measuring stick into my rain gauge to measure how much rain I got last night. Now, I wasn't expecting to see much rain in the rain gauge because the weatherman had given such a low probability of rain. As I was thinking about low probabilities, I pulled out my newly purchased ticket for the $338 million Powerball jackpot, and ripped it up in a fit of disgust over my foolishness for thinking I could beat the highly improbable odds of winning the lottery. Some of the torn pieces of the lottery ticket fell into my rain gauge. But when I bent closer to measure the amount of water in my rain gauge, I noticed that the pieces of lottery ticket were actually floating well above the surface of the water. I realized then that some invisible substance was floating on top of the rain in the rain gauge, suspending the lottery ticket pieces. Now, when I stuck the ruler in the gauge, I measured 3/10 of an inch of rain, and another 7/10 of an inch of this invisible substance that the scraps of lottery ticket paper were floating on top of. Since the weatherman had called for a 30% chance of rain, I concluded that the invisible substance must be improbable rain, and one could use the measurement of actual rain and improbable rain to compute the odds of a rain event. Since potential winning lottery tickets were made out of a substance even more improbable than improbable rain, the paper was able to float on top of the improbable rain."



Mr. Badi-i-sad-o-bist-roz reported his findings to Weather Underground meteorologists, who promptly devised an "improbability float" made out of Powerball lottery tickets that one could put into a rain gauge to measure improbable rain. These new improbability floats were distributed to Weather Underground's entire network of 20,000 personal weather station owners for an experimental study on the nature, sources, and behavior of improbable rain. The results were astonishing. Improbable rain was discovered to always accompany rain, and fall with rain in proportions that allowed one to compute the probability of a rainfall event. Improbable snow was also discovered to exist. However, in some regions, amounts of improbable rain and snow far in excess of what was expected fell, leading to extended periods of really nasty, unseasonably wet weather. Our meteorologists struggled to come up with a scientific explanation for the discrepancies, ruling out the operation of nearby spaceships equipped with improbability drives. Finally, they employed the services of a Native American shaman. The shaman advised them that these highly improbable weather events--most notably the miserably cold, wet, and snowy March 2013 weather in the Eastern United States--were clearly due to curses affecting the region, which drastically affected rain and snow probabilities. "The people have forgotten the old gods," said shaman Norris Ogalallamanna, "and the old gods have become angry, calling down weather curses upon the land. The old gods deemed the Eastern U.S. unworthy of spring this year, and called down a curse to delay it."

The existence of improbable rain and weather curses were quickly seized upon by climate skeptics as evidence that climate models should not be trusted. "The computer climate models used by the National Intergovernmental and Territorial Panel to Investigate Climate Change--NITPICC--utterly failed to anticipate the importance of improbable rain and curses by the old gods on weather and climate," commented spokesman Markoff Chaney of the industry-funded think tank, Let's Attack Science to Protect Profits (LASPP.) The organization maintains of staff of top-notch scientists who swear that their funding from the fossil fuel industry does not affect the objectivity of their science. "This new 'improbability-gate' scandal proves that we can't trust climate models to say diddly-squat that's right about global warming," said Chaney.

The head of NITPICC, and professor of unspeakable truths at Miskatonic University, Dr. R. J. Donteventrytopronouncemylastname, conceded that his organization had some work to do. "We're working very hard to incorporate the effect of improbable rain and curses from the old gods into the NITPICC models," said Dr. Donteventrytopronouncemylastname. "We've gotten approval for dedicated new super-duper computer to model these effects, and we've formed a new Laboratory for Improbable Precipitation Studies (LIPS.) Our first research paper has already been accepted for publication later this millennium in the Journal of Irreproducible Results."

Happy April Fools!

References
Science Made Stupid: How to Discomprehend the World Around Us, by Tom Weller, published 1985.

Other weather and climate April Fools posts
Elderly Obama And Boehner Daughters Arrive In Time Machine To Demand Climate Action, climateprogress.org.
"Scientists Push to Change the Timing of the Seasons", Huffington Post.

Jeff Masters

Humor

Updated: 3:52 PM GMT on April 01, 2013

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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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