Dr. Jeff Masters' WunderBlog

An early start to hurricane season?

By: JeffMasters, 1:12 PM GMT on May 31, 2011

The Atlantic hurricane season officially begins on Wednesday, June 1, but the Caribbean is already showing signs of the change of seasons. Moisture and heavy thunderstorm activity have increased in the region between Central America and Jamaica in recent days, and rainfall amounts of 1 - 2 inches have been common over the past three days over Cuba, Hispaniola, and much of Central America. The subtropical jet stream has been bringing high wind shear of 30 - 50 knots over the Caribbean the past week, but this shear has fallen to 20 - 40 knots this morning, and is predicted to fall below 20 knots by Thursday. All of the computer models predict that an area of low pressure will form in the region between Jamaica and Honduras by Thursday. This low will have the potential to develop into a tropical depression late this week. There is some dry air over the Western Caribbean near Mexico's Yucatan Peninsula that may retard the process, but a surge of moisture accompanying a tropical wave currently passing through the Lesser Antilles may counteract this, when the wave arrives in the Western Caribbean on Thursday. Water temperatures in the Central Caribbean are about 1°C above average, 29°C, which is plenty warm enough to support development of a tropical storm. Some recent runs of the NOGPAS model have predicted development of a tropical depression by late this week, potentially affecting Jamaica and Eastern Cuba. The other models have not been as gung-ho, but have been showing the potential for a strong tropical disturbance with very heavy rains forming late this week. In any case, residents of Jamaica, Cuba, the Cayman Islands, Haiti, Honduras, and Nicaragua should anticipate the possibility that heavy rains of 2 - 4 inches may affect them Thursday through Saturday this week.


Figure 1. Total precipitable water (a measure of how much rain would fall if we condensed all the water vapor present) for May 31, 2011 at 7am EDT. Plentiful water vapor in the SW Caribbean would create about 2 inches of rain (50 mm, orange colors) if it were all condensed out. Image credit: University of Wisconsin CIMSS.

Receipt did not travel 525 miles from Joplin tornado
The May 22 EF-5 tornado that struck Joplin, Missouri did not set a new record for longest transport of debris by a tornado. According to MSNBC, a couple living in Royal Center, Indiana, in North Central Indiana, 525 miles from Joplin, found a receipt from the Joplin Tire store three days after the tornado hit Joplin. However, a press release from Purdue University clarified that the receipt did not arrive via the tornado, but had been left behind by a relative that had visited Joplin before the tornado. The longest distance recorded for debris from a storm was a cancelled check that traveled 210 miles after the 1915 tornado in Great Bend, Kansas.

The death toll from the May 22, 2011 tornado in Joplin, Missouri is 139, although there is still considerable uncertainty about this number. The Joplin tornado is the 8th deadliest in U.S. history, and the most deadly since the 1947 Woodward, Oklahoma twister that killed 181 people. The tornado season of 2011 now has approximately 520 deaths, which would make it the deadliest tornado season since 1936, according to statistics compiled by NOAA. In the 1936 tornado season 552 people died, mostly because of violent tornadoes that hit Tupelo Mississippi (216 killed), and Gainesville, Georgia (203 killed.)


Figure 2. Satellite image taken at 23:45 UTC (7:45pm EDT) May 22, 2011, showing the line of tornadic thunderstorms that spawned the Joplin tornado. Image credit: NOAA Visualization Laboratory.

Jeff Masters

Tornado Hurricane

Updated: 6:18 PM GMT on August 17, 2011

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Invest now to improve tornado warnings; an early start to hurricane season?

By: JeffMasters, 4:24 PM GMT on May 27, 2011

The Atlantic hurricane season officially begin on Wednesday, June 1, and recent computer model runs predict that we may have some early-season action in the Central Caribbean Sea to coincide with the start of this year's season. The GFS, NOGAPS, and ECMWF models have all indicated in some of their recent runs that a tropical disturbance may form between Jamaica and Central America sometime in the May 31 - June 2 time frame, as a lobe of the Eastern Pacific Intertropical Convergence Zone (ITCZ) pushes across Central America into the Caribbean. Up until now, wind shear has been too high to allow tropical storm formation in the Caribbean, due to the presence of the Subtropical Jet Stream. However, this jet is expected to push northwards over Cuba over the coming week, allowing a region of low wind shear to develop over most of the Caribbean. Water temperatures in the Central Caribbean are about 1°C above average, 29°C, which is plenty warm enough to support development of a tropical storm. The main impediment to development will probably be lack of spin, as we don't have any African tropical waves that are expected to enter the Caribbean Sea next week, to help get things spinning. Stay tuned.


Figure 1. Satellite image of Typhoon Songda.

Typhoon Songda heads for Okinawa and Japan
Typhoon Songda brushed the Philippines yesterday, bringing heavy rains that killed at least two people. Fortunately, the brunt of this year's first Category 5 storm missed the islands, and Songda has weakened slightly to a Category 4 storm with 145 mph winds. Songda is turning northwards and will threaten the island of Okinawa on Saturday. Sea surface temperatures decline rapidly north of the Philippines, and Songda is expected to weaken significantly before reaching Okinawa, where sea surface temperatures are approximately 26°C. Wind shear will also increase to high levels by Saturday, and Songda should be at most a Category 2 typhoon by the time it reaches Okinawa. On Sunday,

Invest now for better tornado warnings
National Weather Service forecasters issued a tornado warning 24 minutes in advance of the Joplin, Missouri tornado this.week, which is now being blamed for at least 132 deaths--the deadliest U.S. tornado since at least 1947. However, we can do better, and the National Weather Service Employees Organization (NWSEO) put out a press release on May 23, arguing that investments in weather service forecasting technology are needed to reduce loss of life in future violent tornadoes:

"The 24-minute lead time is a great improvement over the average lead time of 13 minutes for tornado warnings. The meteorologists in the Springfield Weather Forecast Office are commended for their lifesaving work," said Dan Sobien, NWSEO President. "But in our age of advanced technology and communication, when new radars and modeling opportunities exist that can provide more lead time to get people out of the path of a storm, hundreds of people do not have to die because of a tornado event."

Sobien says the Joplin and Tuscaloosa tornadoes are examples of how the government's neglect to invest in NWS related infrastructure over the last 10 to 15 years has failed to provide the tools necessary to protect lives and property. He says that the tools forecasters use to issue tornado warnings are woefully inadequate and that the technology exists to provide lead times so far in advance of the storm that it would make the need for tornado warnings as we know them obsolete. "The much touted Doppler Weather Radar, also known as the Weather Service Radar or WSR-88D, was developed in 1988. Since that time, technological advances, including phased array radars developed by the Department of Defense, have been shown to increase the current lead time on tornado warnings by almost 50 percent."

"The much touted Warn on Forecast process utilizes Meso-scale modeling and has the potential to let forecasters know hours in advance where a thunderstorm would form and if it is likely to contain strong winds, hail, or even a tornado. With adequate staffing, local National Weather Service forecasters who understand local terrain and the model output, could be embedded with emergency managers and decision makers. In the event of a storm, the forecaster could provide emergency managers with the tornado track with some margin of error and people in the way of the storm could be evacuated hours before the tornado hits. This technology is being developed and tested right now, however without funding it will never be available."

"The art and science of severe weather warnings made considerable progress during the 1980s and 90s, going from almost zero lead time to average of about 13 minutes for tornado warnings. However, in recent years, that progress has stalled, even while the technological advancements have accelerated. If the country made the type of investment in the National Weather Service that it did in the 1980s, scenes like the ones in Missouri this week and in Alabama and Mississippi last month could be a thing of the past."

"I am very proud of my co-workers at the National Weather Service this tornado season. They saved many lives and having been there myself, I can assure you, they feel personally about every lost life," said Sobien. "I know that budgets are tight and there are many priorities, but if you put investing in the National Weather Service up to a vote today in tornado alley, I think the approval would be a landslide."


I wholeheartedly agree with this view--investments in better tornado forecasts and tornado observing technology will potentially give us a huge return in lives saved. Have a great holiday weekend, everyone, and I'll be back Monday or Tuesday with a new post.


Jeff Masters

Tornado

Updated: 4:25 PM GMT on May 27, 2011

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No new tornado deaths yesterday; Super Typhoon Songda hits Category 5

By: JeffMasters, 3:04 PM GMT on May 26, 2011

The tornado onslaught of 2011 continued over the Midwest yesterday, as dozens of tornadoes touched down, primarily in Missouri, Illinois, Indiana, and Arkansas. NOAA's Storm Prediction Center logged 81 preliminary reports of tornadoes in eleven states. Even California got into the action, with a tornado near Chico causing minor damage. Mercifully, no deaths were reported from yesterday's tornadoes. Too many thunderstorms formed too close to each other to allow strong or violent tornadoes to grow, as the many thunderstorms interfered with each others' organization. The preliminary tornado count for the 5-day outbreak that began Saturday is 243. Preliminary tornado reports are an overestimate, since some storms get counted multiple times. These over-counts were 35% - 40% in the case of the April 14 - 16 tornado outbreak and April 25 - 28 Super outbreak, so we can expect that the May 21 - 25, 2011 outbreak will end up with close to 150 tornadoes. This would rank as the third largest tornado outbreak in history, giving 2011 the three largest tornado outbreaks of all-time. Prior to 2011, NOAA rated the April 3 - 4, 1974 Super Outbreak as the largest tornado outbreak of all-time, with 148 tornadoes. According to a list of tornado outbreaks maintained by Wikipedia, only two other tornado outbreaks have had as many as 150 twisters prior to 2011--the May 2004 outbreak (385), and the May 2003 outbreak (401). However, these outbreaks occurred over an eight-day and eleven-day period, respectively, and were not due to a single storm system.


Figure 1. Satellite image taken at 23:32 UTC (7:32pm EDT) May 25, 2011, showing a line of tornadic thunderstorms over the Midwest. Image credit: NASA/GSFC.


Figure 2. Tornado near Fariview, Oklahoma, on May 24, 2011. Image credit: Mike Theiss, www.ExtremeNature.com.


Video 1. "We are in the tornado!" is all this poor guy caught in a car during a tornado can say, while buildings fly apart around him. He is very lucky to have survived. Video shot in Navarro County, Texas on May 24, 2011.

The death toll from Tuesday's tornadoes over Oklahoma, Arkansas, and Kansas is now 16, which would bring the death toll from this year's tornadoes to 506, according to yesterday's NOAA tornado statistic update. This makes 2011 the deadliest year for tornadoes in the U.S. since 1953, when 519 people died. That year, three heavily populated cities received direct hits by violent tornadoes. Waco, Texas (114 killed), Flint, Michigan (115 killed), and Worcester, Massachusetts (90 killed) all were hit by violent F-4 or F-5 tornadoes. A similar bad tornado year occurred in 1936, when violent tornadoes hit Tupelo Mississippi (216 killed), and Gainesville, Georgia (203 killed.)

Only a "Slight Risk" day for severe weather today
The Storm Prediction Center has placed portions of twenty states, from Alabama to Vermont, in their "Slight Risk" region for severe weather potential. The slow-moving low pressure system responsible for all the tornado activity this week is weakening, and the primary severe weather threat today is from large hail and damaging straight-line thunderstorm winds. However, there are still likely to be tornadoes today, and I expect we'll see a dozen or so twisters touch down from some of the stronger thunderstorms that develop.


Figure 3. Severe weather threat for Wednesday, May 25, 2011.

Links
Here is an interactive hi-res satellite image showing Joplin before and after the tornado. Some non-interactive images are here.

The New York Times has an interactive tornado fatality map showing how this year's killer tornadoes have mostly clustered over the Southeast U.S., with the glaring exception of the Joplin, Missouri tornado.

NOAA's Visualization Laboratory has an impressive animation of the satellite imagery during the month of April, showing the locations of all the tornadoes as they happened.


Figure 4. Satellite image of Super Typhoon Songda.

Super Typhoon Songda the first Category 5 tropical cyclone of 2011
The first typhoon of 2011 is also the globe's first Category 5 tropical cyclone of the year. Super Typhoon Songda intensified dramatically over the past 24 hours in an environment of light wind shear and warm sea surface temperatures of 30°C, to reach Category 5 status with top sustained winds of 160 mph. Tropical Cyclone Yasi, which devastated Queensland, Australia in early February, was the globe's previous strongest tropical cyclone of 2011, with 155 mph winds.

Fortunately, Songda is expected to miss making a direct hit on the Philippines, though evacuations have been ordered in low-lying areas. Satellite-estimated rainfall for the coming 24-hour period is predicted to be less than 4 inches along the northeast coast of the Philippines' Luzon Island, which should not cause major flooding problems. Songda is expected to turn northwards and threaten the island of Okinawa on Saturday. Sea surface temperatures decline rapidly north of the Philippines, and Songda is expected to weaken significantly before reaching Okinawa, where sea surface temperatures are approximately 26°C. Wind shear will also increase to high levels by Saturday, and Songda should be at most a Category 2 typhoon by the time it reaches Okinawa.

Jeff Masters

Tornado Hurricane

Updated: 9:00 PM GMT on May 26, 2011

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Deadly tornadoes rip OK, KS, and AR; high tornado risk today; Joplin tornado an EF-5

By: JeffMasters, 1:48 PM GMT on May 25, 2011

America's deadliest tornado season since 1953 continued its relentless onslaught of violent tornadoes yesterday. Numerous destructive and deadly tornadoes raked Oklahoma, Texas, Kansas, and Arkansas, killing at least nine people. Yesterday's deadliest tornado hit El Reno and Piedmont, Oklahoma, about 30 miles to the west and northwest of Oklahoma City. Four people died, and one child is missing. Video of the damage from this tornado near the town of Piedmont shot by a news9.com helicopter shows damage characteristic of an EF-4 tornado, with many homes completely demolished and swept off their foundations. This tornado produced a wind gust of 151 mph at an Oklahoma Mesonet station in El Reno, Oklahoma.


Figure 1. Radar reflectivity image of the supercell thunderstorm that spawned the Piedmont, Oklahoma tornado that killed at least four people about 30 miles northwest of Oklahoma City.


Figure 2. Doppler velocity image of the supercell thunderstorm that spawned the Piedmont, Oklahoma tornado.


Figure 3. Top wind gusts recorded by the Oklahoma Mesonet yesterday showed that over 2/3 of the state received gusts of 40 mph or greater, and ten stations got gusts in excess of 58 mph (the definition of a severe thunderstorm.) A remarkable gust of 151 mph was recorded in El Reno, about 30 miles west of Oklahoma City.


Video 1. Chase video of the 1/2-mile wide tornado that killed four people in Canadian/Caddo Counties about 30 miles northwest of Oklahoma City on Tuesday, May 24, 2011.

Joplin, Missouri got a scare last night when Doppler radar showed a rotating thunderstorm approaching the city from the southwest. A tornado warning was issued and the sirens sounded, but the storm passed just to the northwest of the city, bringing Joplin only heavy rains, wind gusts to 41 mph, and intense lightning. A tornado warning forced the evacuation of NOAA's Storm Prediction Center (SPC) in Norman Oklahoma late yesterday afternoon, and the center was out of commission for a 50-minute period. However, yesterday's dangerous tornadoes missed the most heavily populated areas of Oklahoma, and SPC was able to resume normal activity after the storms cleared Oklahoma City. The center logged 47 reports of tornadoes yesterday, bringing the preliminary 4-day total of the current outbreak to 153 twisters. With more tornadoes expected today over a wide swath of the country from Arkansas to Ohio, this week's tornado outbreak is likely to rank as one of the top ten tornado outbreaks in history. This year already has the two largest tornado outbreaks in history, the April 25 - 28 outbreak (327 tornadoes) and the April 14 - 16 outbreak (162 tornadoes.)

This year's tornado death toll is in the 495 - 499 range, making it the deadliest year for tornadoes in the U.S. since 1953, when 519 people died. That year, three heavily populated cities received direct hits by violent tornadoes. Waco, Texas (114 killed), Flint, Michigan (115 killed), and Worcester, Massachusetts (90 killed) all were hit by violent F-4 or F-5 tornadoes. A similar bad tornado year occurred in 1936, when violent tornadoes hit Tupelo Mississippi (216 killed), and Gainesville, Georgia (203 killed.)


Figure 4. Satellite image taken at 22:32 UTC (6:32pm EDT) May 24, 2011, showing a line of tornadic thunderstorms over Oklahoma, Texas, and Kansas. Image credit: NASA/GSFC.


Figure 5. Radar image of an unusual "J"-shaped tendril emerging from a tornadic thunderstorm near Dallas, Texas. This storm had unusually high radar reflectivity (note the pink colors of 70 dbZ echoes), because of large hail in the storm. This thunderstorm produced softball-sized hail (4.5 inch diameter.)


Video 2. Chase video of several Oklahoma tornadoes intercepted yesterday by Reed Timmer of tornadovideos.net.

The Joplin tornado an EF-5, and the costliest tornado in history
The Springfield, Missouri office of the National Weather Service announced yesterday that storm surveys of the 7-mile long, 3/4 mile-wide path of damage carved by the Joplin tornado revealed that winds in the violent tornado exceeded 200 mph, making it the 4th EF-5 tornado of the year. The twister roared through Joplin beginning at 5:41pm CDT on Sunday, May 22. In nine terrifying minutes, the tornado killed at least 125 people, injured 750 more, and destroyed 2,000 buildings. NOAA's Storm Prediction Center (SPC) rates this year's Joplin tornado as the 8th deadliest U.S. tornado of all-time, and the deadliest since at least 1947, when a violent F-5 tornado hit Woodward, Oklahoma, killing 181.

Catastrophe risk modeling firm EQECAT said yesterday that insured damages from the Joplin tornado could be between $1 billion and $3 billion dollars. According to NOAA's National Severe Storm Laboratory, the costliest tornado between 1890 - 1999 was the May 3, 1999 Oklahoma City tornado, which did $1 billion in damage (1999 dollars.) There were no tornadoes during the period 2000 - 2010 capable of causing $1 billion in damage; the only two EF-5 tornadoes during that period, the 2007 Greensburg, Kansas tornado and the 2008 Parkersburg, Iowa tornado each did less than $300 million in damage. Thus, with the possible exception of this year's Tuscaloosa-Birmingham tornado of April 27, the Joplin tornado is probably the most damaging tornado of all-time.

Another "High Risk" day for severe weather and violent tornadoes today
The Storm Prediction Center has placed portions of seven states, from Arkansas to Indiana, in their "High Risk" region for severe weather potential, and warn of the potential for long-lived strong or violent tornadoes. This is their second consecutive "High Risk" forecast day, and fourth of the year. A high risk forecast was also issued on April 27, which was the busiest tornado day in world history, with 198 tornadoes occurring in a 24-hour period. Over 300 people died. The other "High Risk" forecast by SPC came during the final day of the April 14 - 16 outbreak over the Southeast U.S. Fifty-two tornadoes hit that day, and 26 people died in North Carolina and Virginia. The severe weather threat will diminish considerably on Thursday, when only a slight risk of severe weather is expected from Alabama to New York.


Figure 5. Severe weather threat for Wednesday, May 25, 2011.

Joplin tornado the 7th U.S. billion-dollar weather disaster of 2011
The Joplin tornado is the 7th U.S. weather disaster of 2011 costing more than a billion dollars. With hurricane season still to come, 2011 has an excellent chance of beating 2008's record of nine billion-dollar weather disasters. The billion dollar weather disasters of 2011 so far:

1) 2011 Groundhog Day's blizzard ($1- $4 billion)
2) April 3 -5 Southeast U.S. severe weather outbreak ($2 billion)
3) April 8 - 11 severe weather outbreak ($2.25 billion)
4) April 25 - 28 super tornado outbreak ($3.5 - $6 billion)
5) Mississippi River flood of 2011 ($9 billion)
6) Texas drought ($1.2 billion)
7) Joplin tornado ($1 - $3 billion)

Links
The New York Times has an interactive tornado fatality map showing how this year's killer tornadoes have mostly clustered over the Southeast U.S., with the glaring exception of the Joplin, Missouri tornado.

NOAA's Visualization Laboratory has an impressive animation of the satellite imagery during the month of April, showing the locations of all the tornadoes as they happened.

Helping out tornado victims
For those who want to lend a helping hand to those impacted by the widespread destruction this month's severe weather has brought, stop by the Red Cross website, or portlight.org blog. Portlight has been very active bringing aid to the victims of this year's tornadoes.

Jeff Masters

Tornado

Updated: 10:48 PM GMT on May 25, 2011

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Joplin tornado toll at 116; dangerous tornado outbreak expected today

By: JeffMasters, 1:50 PM GMT on May 24, 2011

Severe weather is expected again today in storm-torn Joplin, Missouri, as rescuers sift through the rubble of their town that was devastated by the deadliest U.S. tornado since at least 1947. A violent high-end EF-4 tornado with winds of 190 – 198 mph carved a 7-mile long, ¾ to one mile-wide path of near-total destruction through Joplin beginning at 5:41pm CDT Sunday evening. In nine terrifying minutes, the tornado killed at least 116 people, injured 500 more, and obliterated huge sections of the town. Damage from the tornado is so severe that pavement was ripped from the ground, and the level of damage is so extreme that this is likely to surpass last month's Tuscaloosa-Birmingham tornado as the costliest tornado of all-time.


Figure 1. Radar reflectivity image of the supercell thunderstorm that spawned the Joplin, Missouri tornado, one minute before the tornado touched down at 5:41pm CDT. There is a hook echo apparent, though not a classic well-defined one.


Figure 2. Radar-estimated rainfall for the period May 22 – 24 over the region surrounding Joplin. Rains of 1.83" fell on the city yesterday, a record for the date.

The Joplin tornado's place in history
According to our weather historian, Christopher C. Burt in his post, The World's Deadliest Tornadoes, the death toll of 116 from the Joplin tornado ranks as the deadliest U.S. tornado since at least 1947, when a violent F-5 tornado hit Woodward, Oklahoma, killing 181. However, it is now thought that the Woodward tornado was actually one of a series of tornadoes, and the tornado that hit Woodward killed 107 people. If that is true, we have to back all the way to 1936 to find the last U.S. tornado that killed more people than 2011's Joplin tornado. In 1936, violent tornadoes a day apart hit Tupelo Mississippi (216 killed), and Gainesville, Georgia (203 killed.) NOAA's Storm Prediction Center (SPC) rates this year's Joplin tornado as the 9th deadliest U.S. tornado of all-time.

This year's tornado death toll now stands at 482, making it the deadliest year for tornadoes in the U.S. since 1953, when 519 people died. That year, three heavily populated cities received direct hits by violent tornadoes. Waco, Texas (114 killed), Flint, Michigan (115 killed), and Worcester, Massachusetts (89 – 94 killed) all were hit by violent F-4 or F-5 tornadoes. A similar bad tornado year occurred in 1936, when violent tornadoes hit Tupelo Mississippi (216 killed), and Gainesville, Georgia (203 killed.)


Video 1. The last year with more tornado deaths than 2011 was 1953, when three great tornadoes killed more than 90 people each. This old newsreel video shows destruction from the first of these deadly 1953 tornadoes, the May 11, 1953 F-5 tornado that hit downtown Waco Texas, killing 114 people. The wunderground youtube channel has almost 300 old newsreel videos of historically significant weather events.

What's going on?
It's been an incredibly dangerous and deadly year for tornadoes. On April 14 - 16, we had the largest tornado outbreak in world history, with 162 tornadoes hitting the Southeast U.S. That record lasted just two weeks, when the unbelievable April 25 – 28 Super Outbreak hit. Unofficially, that outbreak had 327 tornadoes, more than double the previous record. The legendary April 3 – 4 1974 Super Outbreak has now fallen to third place, with 148 tornadoes. Damage from the April 25 – 28, 2011 outbreak was estimated to be as high as $5 billion, making it the most expensive tornado outbreak in history; the Tuscaloosa-Birmingham tornado of April 27 may end up being the most expensive tornado of all-time—until the damage from Sunday's Joplin tornado is tabulated. Officially, 875 tornadoes hit the U.S. In April 2011, making it the busiest tornado month in history. The previous record was 542 tornadoes, set in May 2003. The previous April tornado record was 267, set in 1974, and April has averaged just 161 tornadoes over the past decade.

So what's going on? Why are there so many tornadoes, and so many people getting killed? Well, the high death toll this year is partly just bad luck. Violent EF-4 and EF-5 tornadoes usually miss heavily populated areas, and we've had the misfortune of having two such tornadoes track over cities with more than 50,000 people (the Joplin tornado, and the Tuscaloosa-Birmingham EF-4 tornado in Alabama, which killed 61 people on April 27.) This sort of bad luck occurred in both 1953, when F-5 tornadoes hit Flint, Worcester, and Waco, and in 1936, when F-5s hit Tupelo and Gainesville. However, this year's death toll is more remarkable than the 1953 or 1936 death tolls, since in 2011 we have Doppler radar and a modern tornado warning system that is very good at providing an average of twelve minutes of warning time. The warning time for the Joplin tornado was 24 minutes. The first tornado warning wasn't issued until 1948, and virtually all tornadoes from the 1950s and earlier hit with no warning. On average, tornado deaths in the United States decreased from 8 per 1 million people in 1925 to 0.12 per 1 million people in 2000. Had this year's tornadoes occurred 50 years ago, I expect the death toll would have exceeded three thousand.


Figure 3. Number of strong to violent EF-3, EF-4 and EF-5 tornadoes from 1950 to 2011. There are no obvious trends in the numbers of these most dangerous of tornadoes. Image credit: NOAA/National Climatic Data Center (updated using stats for 2008 – 2011 from Wikipedia.)

Tornadoes require two main ingredients for formation—instability and wind shear. Instability is at a maximum when there is record warm air with plenty of moisture at low levels, and cold dry air aloft. April 2011 sea surface temperature in the Gulf of Mexico were at their third highest levels of the past 100 years, so there was plenty of warm, moist air available to create high instability, whenever approaching storm systems pulled the Gulf air northwards into Tornado Alley, and brought cold, dry air south from Canada. The La Niña event in the Eastern Pacific, in part, caused this spring's jet stream to have very strong winds that changed speed and direction with height. This sort of shearing force (wind shear) was ideal for putting a twist on thunderstorm updrafts, allowing more numerous and more intense tornadoes than usual to occur. Was this year's heightened wind shear and instability the result of climate change? We don't know. Over the past 30 years, there have not been any noticeable trends wind shear and instability over the Lower Mississippi Valley, according to the NOAA Climate Scene Investigations team. Furthermore, there have been no upward trend in the number of violent EF-4 and EF-5 tornadoes over the past 60 years, or in the number of EF-3 and stronger tornadoes (Figure 3.) However, this year's remarkable violent tornado activity—17 such tornadoes, with tornado season a little more than half over—brings our two-year total for the decade of 2010 – 2019 to 30. At this rate, we'll have more than 150 violent tornadoes by decade's end, beating the record of 108 set in the 1950s. In summary, this year's incredibly violent tornado season is not part of a trend. It is either a fluke, the start of a new trend, or an early warning symptom that the climate is growing unstable and is transitioning to a new, higher energy state with the potential to create unprecedented weather and climate events. All are reasonable explanations, but we don't have a long enough history of good tornado data to judge which is most likely to be correct.

More severe weather today
Yesterday, survivors of the tornado endured a 12-hour period with two severe thunderstorm warnings, a record 1.83” of rain, hail, and lightning that struck two police officers. NOAA's Storm Prediction Center (SPC) recorded 11 preliminary reports of tornadoes yesterday, along with 315 reports of damaging winds and 182 reports of hail up to 3.5” in diameter. The severe weather threat is much higher today, and SPC has placed a large section of eastern Kansas and eastern Oklahoma in their "High Risk" region for severe weather potential, and warn of the potential for long-lived strong tornadoes. This is their third "High Risk" forecast for the year, and the first since the terrible April 27, 2011 tornado outbreak. That day was the busiest tornado day in world history, with 198 tornadoes occurring in a 24-hour period. Over 300 people died. The other "High Risk" forecast by SPC came during the final day of the April 14 – 16 outbreak over the Southeast U.S. Fifty-two tornadoes hit that day, and 26 people died in North Carolina and Virginia. The severe weather threat will continue into Wednesday, when additional tornadoes are likely along a swath from Arkansas to Indiana.


Figure 4. Severe weather threat for Tuesday, May 23, 2011.

Links
The most remarkable audio I've ever heard of people surviving a direct hit by a violent tornado was posted to Youtube by someone who took shelter in the walk-in storage refrigerator at a gas station during the Joplin tornado. There isn't much video.


Video 2. Video of the Joplin, Missouri tornado of May 22, 2011, entering the southwest side of town. Filmed by TornadoVideos.net Basehunters team Colt Forney, Isaac Pato, Kevin Rolfs, and Scott Peake.

Helping out tornado victims
For those who want to lend a helping hand to those impacted by the widespread destruction this month's severe weather has brought, stop by the Red Cross website, or portlight.org blog. Portlight has been very active bringing aid to the victims of this year's tornadoes. Below is the damage survey from the Joplin tornado:

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE SPRINGFIELD MO
938 PM CDT MON MAY 23 2011

...JOPLIN TORNADO GIVEN A PRELIMINARY HIGH END EF-4 RATING...

* DATE...22 MAY 2011
* BEGIN LOCATION...APPROXIMATELY 3 MILES SOUTHWEST OF JOPLIN
* END LOCATION...1 MILE SOUTHEAST OF DUQUESNE
* ESTIMATED BEGIN TIME...541 PM
* ESTIMATED END TIME...550 PM
* MAXIMUM EF-SCALE RATING...EF-4
* ESTIMATED MAXIMUM WIND SPEED...190-198 MPH
* ESTIMATED PATH WIDTH...3/4 OF A MILE
* PATH LENGTH...7 MILES
* FATALITIES...116 REPORTED AS OF 3 PM MONDAY
* INJURIES...400 REPORTED AS OF 3 PM MONDAY
* BEGIN LAT/LON...37.06 N / 94.57 W
* END LAT/LON...37.06 N / 94.39 W

NATIONAL WEATHER SERVICE SURVEY TEAMS RATED THE TORNADO THAT KILLED OVER 100 PEOPLE IN AND AROUND JOPLIN AS A HIGH END EF-4 TORNADO.

BASED UPON SURVEYS COMPLETED TODAY...MAXIMUM WINDS WERE ESTIMATED BETWEEN 190 AND 198 MPH. THE TORNADO HAD A MAXIMUM WIDTH OF 3/4 TO ONE MILE.

THE TORNADO INITIALLY TOUCHED DOWN AROUND 541 PM NEAR THE INTERSECTION OF COUNTRY CLUB AND 32ND STREET. ADDITIONAL SURVEYS ARE EXPECTED TO BE CONDUCTED TO FURTHER DEFINE THE STARTING POINT AND INTENSITY AT THIS LOCATION.

DAMAGE BECAME MORE WIDESPREAD AS THE TORNADO CROSSED MAIDEN LANE...CAUSING SIGNIFICANT DAMAGE TO NEARLY ALL WINDOWS ON THREE SIDES OF ST JOHNS HOSPITAL AS WELL AS TO THE ROOF. THE TORNADO FURTHER INTENSIFIED AS IT DESTROYED NUMEROUS HOMES AND BUSINESSES TO THE EAST AND NORTH OF THE HOSPITAL. THE HIGHEST RATED DAMAGE IN THIS AREA WAS TO A CHURCH SCHOOL THAT HAD ALL BUT A PORTION OF ITS EXTERIOR WALLS DESTROYED AS WELL AS TO A NURSING HOME. WINDS IN THAT AREA WERE ESTIMATED AT 160 TO 180 MPH.

THE TORNADO CONTINUED TO DESTROY OVER 100 HOMES BETWEEN 32ND AND 20TH STREETS. THREE STORY APARTMENT COMPLEXES HAD THE TOP TWO FLOORS REMOVED...OTHER TWO STORY COMPLEXES WERE PARTIALLY LEVELED.

A BANK WAS TOTALLY DESTROYED WITH THE EXCEPTION OF THE VAULT.

A DILLONS GROCERY STORE ALSO HAD SIGNIFICANT ROOF AND EXTERIOR WALL DAMAGE. LASTLY...THE EXTERIOR AND INTERIOR WALLS OF A TECHNICAL SCHOOL...A MORTAR AND REBAR REINFORCED CINDER BLOCK BUILDING...FAILED.

THE TORNADO CROSSED RANGELINE ROAD NEAR 20TH STREET. THE MOST INTENSE DAMAGE WAS NOTED JUST EAST OF THIS INTERSECTION WHERE A HOME DEPOT WAS DESTROYED BY AN ESTIMATED 190 TO NEARLY 200 MPH WINDS.
IN ADDITION...THE CUMMINS BUILDING...A CONCRETE BLOCK AND HEAVY STEEL BUILDING...HAD ITS STEEL ROOF BEAMS COLLAPSE. SPORTS ACADEMY AND THE WALMART ALSO SUFFERED SIGNIFICANT DAMAGE.

THE TORNADO CONTINUED TO MOVE EASTWARD ALONG AND SOUTH OF 20TH STREET DESTROYING NUMEROUS WAREHOUSE STYLE FACILITIES AND RESIDENCES THROUGH DUQUESNE ROAD. WINDS IN THIS AREA MAY ALSO APPROACH 200 MPH.

THE TORNADO CONTINUED TO DESTROYING NUMEROUS HOMES BEFORE WEAKENING AS IT TURNED SOUTHEAST TOWARD INTERSTATE 44.

SUBSEQUENT DAMAGE SURVEYS WILL BE REQUIRED TO DETERMINE THE SCOPE OF ADDITIONAL REPORTS ALONG AND SOUTHEAST OF THE INTERSECTION OF HIGHWAY 71 AND INTERSTATE 44.

FOR REFERENCE...THE ENHANCED FUJITA SCALE CLASSIFIES TORNADOES INTO THE FOLLOWING CATEGORIES:

EF0...WIND SPEEDS 65 TO 85 MPH.
EF1...WIND SPEEDS 86 TO 110 MPH.
EF2...WIND SPEEDS 111 TO 135 MPH.
EF3...WIND SPEEDS 136 TO 165 MPH.
EF4...WIND SPEEDS 166 TO 200 MPH.
EF5...WIND SPEEDS GREATER THAN 200 MPH.

Jeff Masters

Tornado

Updated: 7:59 PM GMT on May 24, 2011

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Deadliest U.S. tornado since 1953 rips through Joplin, Missouri, killing 89

By: JeffMasters, 2:11 PM GMT on May 23, 2011

The incredibly violent tornado season of 2011 struck another sickening blow last night, when a violent tornado carved a ½ – ¾ mile-wide path of devastation through Joplin, Missouri. At least 89 people died, hundreds were injured, and huge sections of the town virtually obliterated. Damage from the tornado is so severe that pavement was ripped from the ground, which is characteristic of a top-end EF-5 tornado with winds in excess of 200 mph. This was almost certainly a least an EF-4 tornado with winds over 166 mph, and the level of damage is so extreme that this is likely to surpass last month's Tuscaloosa-Birmingham tornado as the costliest tornado of all-time.


Figure 1. Cars stacked on top of each other in front of the heavily damaged St. Johns Regional Medical Center after the May 22, 2011 tornado in Joplin, Missouri. Note the pavement ripped up from the road and piled in front of the cars. Tornadoes powerful enough to rip up pavement are frequently classified as EF-5 with winds in excess of 200 mph. Image credit: Chris McCrillis, posted to Twitter.

The huge supercell thunderstorm that spawned the Joplin tornado formed over extreme southeast Kansas yesterday afternoon, along the boundary between warm, moist air flowing northwards from the Gulf of Mexico, and cold, dry air moving south from Canada. NOAA's Storm Prediction Center (SPC) had put the region in its “moderate risk” region for severe weather. As the supercell moved into Southwest Missouri, it spawned the tornado that roared through Joplin at 5:45pm CDT. This storm generated other tornadoes, straight-line wind damage, and flash flooding from torrential rains that exceeded six inches as it moved east southeast across Southwest Missouri. SPC recorded 48 preliminary reports of tornadoes yesterday, bringing the 2-day total for the current outbreak to 70. A tornado also killed one person and injured 22 in Minneapolis Sunday. Separate tornadoes killed one person each in Andice, Texas and Reading, Kansas on Saturday—the first tornado deaths in the U.S. since the April 25 – 28 Super Outbreak.


Figure 2. Radar reflectivity image of the supercell thunderstorm that spawned the Joplin, Missouri tornado, ½ hour after it devastated the city (circle with the “+” symbol.)


Figure 3. Radar Doppler velocity image of the supercell thunderstorm that spawned the Joplin, Missouri tornado, ½ hour after it devastated the city (circle with the “+” symbol.)


Figure 4. Satellite image taken at 5:45pm CDT May 22, 2011, when the Joplin, Missouri tornado was occurring. Image credit: NASA/GSFC.

Deadliest tornado since 1953
Yesterday's Joplin, Missouri tornado is the deadliest single tornado in the U.S. since June 10, 1953, when 94 people died in the Worcester, Massachusetts tornado. The previous deadliest tornado in the past 50 years occurred just last month, when 65 people died in the Tuscaloosa-Birmingham EF-4 tornado in Alabama. This year's tornado death toll now stands at 455, making it the deadliest year for tornadoes in the U.S. since 1953, when 519 people died. The deadliest year was 1925, with 794 deaths. That was the year of the deadliest U.S. tornado of all-time, the great Tri-State tornado, which killed 695 people in Missouri, Illinois, and Indiana.

More severe weather today
NOAA's Storm Prediction Center has placed a large section of the Midwest U.S., including portions of Oklahoma, Kansas, Missouri, Illinois, Ohio, Michigan, and Pennsylvania, in its “moderate risk” region for severe weather today. The threat of tornadoes will not be as great today as yesterday, with today's main threat being large hail and damaging straight-line thunderstorm winds. However, I do expect we will see a dozen or so tornadoes today, and residents of the at-risk area need to keep in mind the deadly history of this storm system. The severe weather threat will continue into Tuesday, when additional tornadoes are likely over Oklahoma, Kansas, and Southwest Missouri. A severe thunderstorm roared through Joplin between 8:30am and 9am CDT this morning, bringing heavy rain, small hail, and wind gusts to 36 mph. Undoubtedly, this storm frayed some nerves, and the city will remain at risk of seeing more severe thunderstorms through Tuesday night.


Figure 5. Severe weather threat for Monday, May 23, 2011.

Links
The most remarkable audio I've ever heard of people surviving a direct hit by a violent tornado was posted to Youtube by someone who took shelter in the walk-in storage refrigerator at a gas station during the Joplin tornado. There isn't much video. We won't see a lot of spectacular videos of the Joplin tornado, since it was wrapped in rain and difficult to see.

Listen to my 12-minute interview on the historic April 2011 tornadoes for EarthSky.org, which aired on NPR earlier this month. I discuss how climate change might impact severe weather and tornadoes.

Our weather historian, Christopher C. Burt, has an excellent post on The World's Deadliest Tornadoes.

My 2008 post, Are tornadoes getting stronger and more frequent? The answer is--we don't know.


Figure 6. The Portlight relief trailer being loaded in Summerville, SC, in preparation for a journey to the April tornado disaster zone.

Helping out tornado victims
For those who want to lend a helping hand to those impacted by the widespread destruction this spring's severe weather has brought, stop by the Red Cross website, or portlight.org blog. Portlight has been very active bringing aid to the victims of this year's tornadoes.

Jeff Masters

Tornado

Updated: 1:45 AM GMT on May 24, 2011

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Mississippi River flood of 2011 sets all-time flow record, but has crested

By: JeffMasters, 2:43 PM GMT on May 20, 2011

The great Mississippi River flood of 2011 crested yesterday and today, and the volume of water being pushed toward the Gulf of Mexico is the largest ever recorded on the Mississippi, said Bob Anderson, a spokesman for the Army Corps of Engineers for the Mississippi Valley Division. "It's never been this high; it's never had this much water," he said. "There's just a tremendous amount of strain on these levees." The Mississippi crested yesterday at Vicksburg, Mississippi, reaching 57.06'. This exceeded the previous all-time record of 56.2', set during the great flood of 1927. The river crested at Natchez, Mississippi early this morning, and is now falling. The flood height at Natchez was also the greatest on record--61.91', nearly three feet higher than the previous record height of 58', set in 1937. The opening of the Morganza Spillway on Saturday helped to reduce the flood heights from Vicksburg to New Orleans by 1 - 3 feet, greatly reducing the pressure on the levees and on the critical Old River Control Structure (which, as I discussed last Friday, is America's Achilles' heel, and must be protected.) According the National Weather Service, the Mississippi River is no longer rising anywhere along its length, and the great flood of 2011 has likely seen its peak. Rainfall over the next five days will not be enough to raise the Mississippi River water levels above the crests recorded yesterday and today. While it is great news that the flood has peaked, and the Old River Control Structure and all of the mainline levees on the Mississippi River have held, the fight is not over yet. Water levels will stay high for many weeks, and these structures will take a sustained pounding that could still cause failures. If another incredible heavy rain event like we experienced in mid-April occurs in June, the levee system and Old River Control Structure will threatened. Let's hope we don't have an early season Gulf of Mexico tropical storm that makes landfall over Louisiana. The latest 2-week forecast from the GFS model is not hinting at anything like this, fortunately. It's a good thing (for the sake of the levees) that Louisiana experienced severe drought over the winter and spring--had the water levels been high throughout winter and spring, like occurred in the run-up to the great 1927 flood, the levees would have been soggy and much more vulnerable to failure once the big flood crest hit.


Figure 1. The flow of the Mississippi River past the Old River Control Structure near Simmesport, Louisiana reached its all-time highest volume on record Thursday, when the flow rate hit 2.3 million cubic feet per second (cfs). The flow of Niagara Falls at normal water levels is 100,000 cfs, so the Mississippi's flow was 23 times that of Niagara Falls. Image credit: Army Corps of Engineers.

Recommended reading
My post on the Old River Control Structure, America's Achilles' heel: the Mississippi River Old River Control Structure, is well worth reading, if you haven't done so. I plan on making a follow-up post next week discussing the economic cost of the failure of this critical flood-control structure.

Our weather historian, Christopher C. Burt, has made a very interesting post on the greatest floods to affect each continent.


Figure 2. Track forecast for Tropical Storm Four.

First typhoon of 2011 coming?
In the Northwest Pacific, Tropical Storm Four has formed, and appears poised to become the first typhoon of 2011 by early next week. The storm is expected to head west-northwest or northwest towards the Philippines. While the GFS model predicts Tropical Storm Four will miss the Philippines and recurve northwards towards Japan late next week, it is too early to be confident of this forecast.

Have a great weekend everyone, and I'll be back Monday with a new post.

Jeff Masters

Flood

Updated: 3:40 PM GMT on May 20, 2011

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NOAA predicts an active Atlantic hurricane season: 15 named storms, 8 hurricanes

By: JeffMasters, 4:08 PM GMT on May 19, 2011

The National Oceanic and Atmospheric Administration (NOAA) issued its 2011 Atlantic hurricane season forecast today. NOAA forecasts a very active and possibly hyperactive season. They give a 65% chance of an above-normal season, a 25% chance of a near-normal season, and just a 10% chance of a below-normal season. NOAA predicts a 70% chance that there will be 12 - 18 named storms, 6 – 10 hurricanes, and 3 - 6 major hurricanes, with an Accumulated Cyclone Energy (ACE) 105% - 200% of the median. If we take the midpoint of these numbers, NOAA is calling for 15 named storms, 8 hurricanes, 4.5 major hurricanes, and an ACE index 152% of normal. A season with an ACE index over 165% is considered "hyperactive." An average season has 10 – 11 named storms, 6 hurricanes, and 2 intense hurricanes. Hurricane seasons during 1995-2010 have averaged about 15 named storms, 8 hurricanes, and 4 major hurricanes, with an ACE index 151% of the median. NOAA classifies 11 of the 16 seasons since 1995 as above normal, with eight being hyperactive. Only five seasons since 1995 have not been above normal, which include four El Niño years (1997, 2002, 2006, and 2009), and the 2007 season.

The forecasters cited the following main factors that will influence the coming season:

1) Above-average sea surface temperatures (SSTs) are expected in the hurricane Main Development Region (MDR), from the Caribbean to the coast of Africa between between 10°N and 20°N. SSTs in the MDR during April were about 0.5°C above average, the 14th warmest April SSTs in the past 100 years. This is far below last year's record 1.4°C anomaly, but still plenty warm enough to help drive above-average Atlantic hurricane activity. Long-range computer forecast models are predicting a continuation of these above-average SSTs through the peak part of hurricane season.

2) We are in an active period of hurricane activity that began in 1995, thanks to a natural decades-long cycle in hurricane activity called the Atlantic Multidecadal Oscillation (AMO): "During 1995-2010, some key aspects of the tropical multi-decadal signal within the MDR have included warmer than average SSTs, reduced vertical wind shear and weaker easterly trade winds, below-average sea-level pressure, and a configuration of the African easterly jet that is more conducive to hurricane development from tropical waves moving off the African coast. Many of these atmospheric features typically become evident during late April and May, as the atmosphere across the tropical Atlantic and Africa begins to transition into its summertime monsoon state."

3) An El Niño event is not expected this year: "Another climate factor known to significantly impact Atlantic hurricane activity is the El Niño-Southern Oscillation (ENSO.) The three phases of ENSO are El Niño, La Niña, and ENSO-Neutral. El Niño events tend to suppress Atlantic hurricane activity, while La Niña events tend to enhance it (Gray 1984). Currently, the 2010-11 La Niña episode is dissipating. Based on observations and ENSO forecast models, ENSO-Neutral conditions are likely during the 2011 Atlantic hurricane season."

4) NOAA is increasingly using output from ultra-long range runs of the computer forecast models we rely on to make day-to-day weather forecasts, for their seasonal hurricane forecasts: "The outlook also takes into account dynamical model predictions from the NOAA Climate Forecast System (CFS), the European Centre for Medium Range Weather Forecasting (ECMWF), the United Kingdom Meteorology (UKMET) office, and the EUROpean Seasonal to Inter-annual Prediction (EUROSIP) ensemble. These models are indicating a high likelihood of an above normal season."

How accurate are the NOAA seasonal hurricane forecasts?
A talk presented by NHC's Eric Blake at the 2010 29th Annual AMS Conference on Hurricanes and Tropical Meteorology studied the accuracy of NOAA's late May seasonal Atlantic hurricane forecasts, using the mid-point of the range given for the number of named storms, hurricanes, intense hurricanes, and ACE index. Over the past twelve years, a forecast made using climatology was in error, on average, by 3.6 named storms, 2.5 hurricanes, and 1.7 intense hurricanes. NOAA's May forecast was not significantly better than climatology for these quantities, with average errors of 3.5 named storms, 2.3 hurricanes, and 1.4 intense hurricanes. Only NOAA's May ACE forecast was significantly better than climatology, averaging 58 ACE units off, compared to the 74 for climatology. Using another way to measure skill, the Mean Squared Error, May NOAA forecasts for named storms, hurricanes, and intense hurricanes had a skill of between 5% and 21% over a climatology forecast (Figure 2). Not surprisingly, NOAA's August forecasts were much better than the May forecasts, and did significantly better than a climatology forecast.


Figure 1. Mean absolute error for the May and August NOAA seasonal hurricane forecasts (1999 - 2009 for May, 1998 - 2009 for August), and for forecasts made using climatology from the past five years. A forecast made using climatology was in error, on average, by 3.6 named storms, 2.5 hurricanes, and 1.7 intense hurricanes. NOAA's May forecast was not significantly better than climatology for these quantities, with average errors of 3.5 named storms, 2.3 hurricanes, and 1.4 intense hurricanes. Only NOAA's May ACE forecast was significantly better than climatology, averaging 58 ACE units off, compared to the 74 for climatology. Image credit: Verification of 12 years of NOAA seasonal hurricane forecasts, National Hurricane Center.

How do NOAA's seasonal hurricane forecasts compare to CSU and TSR?
Two other major seasonal hurricane forecasts will be released over the next two weeks. On June 1, Phil Klotzbach and Bill Gray of Colorado State University (CSU) issue their forecast, and the British firm Tropical Storm Risk (TSR) will issue their outlook on May 24. A three-way comparison of the forecast accuracy of the three groups' forecast (Figure 2) reveals that all three organizations enjoy some success at making accurate seasonal forecasts, with NOAA and CSU making the best late May/early June forecasts overall. While the skill of these forecasts is low, they are useful for businesses such as the insurance industry.


Figure 2. Comparison of the percent improvement over climatology for May and August seasonal hurricane forecasts for the Atlantic from NOAA, CSU and TSR from 1999-2009 (May) and 1998-2009 (August). using the Mean Squared Error. Image credit: Verification of 12 years of NOAA seasonal hurricane forecasts, National Hurricane Center.

Jeff Masters

Hurricane

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PSU Atlantic hurricane season forecast: 16 named storms

By: JeffMasters, 3:25 PM GMT on May 18, 2011

Expect a busy Atlantic hurricane season this year, with sixteen named storms, say Pennsylvania State University (PSU) hurricane scientists Michael Mann and Michael Kozar. Their annual Atlantic hurricane season forecast issued on May 16 calls for 12 - 20 named storms this season, which starts June 1 and runs until November 30. An average season has 10 - 11 named storms. Their prediction was made using statistics of how past hurricane seasons have behaved in response to sea surface temperatures (SSTs), the El Niño/La Niña oscillation, the North Atlantic Oscillation (NAO), and other factors. This year's forecast is primarily based on three factors:

1) The current above-average sea surface temperatures in the Atlantic Main Development Region (MDR) for hurricanes, from Central America to the coast of Africa between 10°C and 20°C North latitude, will continue into the main part of hurricane season;
2) The fading La Niña event in the Eastern Pacific Ocean will be replaced by neutral El Niño/La Niña conditions;
3) The North Atlantic Oscillation (NAO) will be near average during hurricane season.


Figure 1. Hurricane Igor of 2010 as seen from the International Space Station.

The PSU team will also be making a new experimental forecast based not on the absolute MDR sea surface temperatures, but on difference between the MDR SST and ocean temperatures over the rest of the globe's tropical oceans. Some research has suggested that Atlantic hurricane activity is greater when this relative difference in SSTs is high, not necessarily when the absolute MDR SST is high (in other words, if all the world's tropical oceans have record high SSTs, we wouldn't get an unusually active Atlantic hurricane season, even with record warm SSTs in the Atlantic.) This new experimental forecast is predicting higher activity: 19 named storms in the Atlantic this year.

The PSU team has been making Atlantic hurricane season forecasts since 2007, and these predictions have done pretty well:

2007 prediction: 15 Actual: 15
2009 prediction: 12.5 Actual: 9
2010 prediction: 23 Actual: 19

NOAA will be issuing their annual pre-season Atlantic hurricane season forecast at 11:30am on Thursday, and I'll make a post on that Thursday afternoon. Tropical Storm Risk, Inc. (TSR) issues their pre-season forecast on May 24, and Colorado State University issues theirs on June 1.

My next post on the Mississippi flood will be on Friday.

Links:

PSU 2011 Atlantic hurricane season forecast issued on May 16.

Jeff Masters

Hurricane

Updated: 3:32 PM GMT on May 18, 2011

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La Niña fades to neutral; April the globe's 4th - 7th warmest on record

By: JeffMasters, 3:12 PM GMT on May 17, 2011

April 2011 was the globe's 7th warmest April on record, according to the National Oceanic and Atmospheric Administration (NOAA) National Climatic Data Center (NCDC). NASA's Goddard Institute for Space Studies rated April the 4th warmest on record, tied with April 2005. April 2011 global ocean temperatures were the 11th warmest on record, and land temperatures were the 6th warmest on record. The UK had its hottest April on record, with rainfall only 21% of average. Huge fires burned through Scotland, England, and Northern Ireland, fanned by strong spring winds.


Figure 1. Departure of temperature from average for April, 2011. Image credit: National Climatic Data Center (NCDC).

La Niña fades to neutral
The La Niña that began in June 2010 is now transitioning to neutral conditions, according to the Climate Prediction Center. Sea surface temperatures (SSTs) in the equatorial Pacific off the coast of South America are now just 0.4°C below average, the first time since June 2010 that these temperatures have not been 0.5°C or more cooler than average, the threshold for a La Niña. However, it is possible that these water could cool a bit again over the next few weeks, so NOAA has not yet declared an official end to this La Niña episode. Equatorial SSTs were 0.5°C below average in the central Pacific, and average to above-average temperatures have emerged in the eastern Pacific. While this signals the end to La Niña, the CPC cautions that the atmosphere is still behaving like La Niña is continuing. An animation of SSTs since February shows the weakening La Niña nicely. Springtime is the most common time for a La Niña event to end; since 1950, half of all La Niñas ended in March, April, or May.

Arctic sea ice 5th lowest on record
Arctic sea ice declined slowly through most of April, and had the 5th lowest extent since satellite record began in 1979, according to the National Snow and Ice Data Center. However, sea ice extent began declining more quickly toward the end of the month, and as of May 16 was the second lowest on record.

I'll have more on the Mississippi River flood next post. If you haven't seen it, read my post, America's Achilles' heel: the Mississippi River Old River Control Structure.

Jeff Masters and Angela Fritz

Angela is a new wunderground hire, with a Masters degree in Meteorology, who will be helping out with my blog and the site's weather education and climate change content.

Climate Summaries

Updated: 5:41 PM GMT on May 17, 2011

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Unprecented floods on the Mississippi, in Colombia, and Canada

By: JeffMasters, 2:58 PM GMT on May 16, 2011

The great Mississippi River flood of 2011 continues to make history, with Saturday's opening of the flood gates of the Morganza Spillway marking just the second time that flood control structure has been used since its construction in 1956. With the Morganza, Bonnet Carre', and Birds Point-New Madrid Spillways all open, the Army Corps of Engineers has now opened all of its major spillways simultaneously for the first time ever. The Mississippi is rising at Vicksburg, Mississippi, where the water has now reached 56.5', exceeding the previous all-time record of 56.2', set during the great flood of 1927. Natchez, Mississippi, is also at its greatest flood height on record, with the water at 60.6'. The previous record high was 58', set in 1937. However, the opening of the Morganza spillway has reduced the predicted heights of the great flood of 2011 from Natchez to New Orleans by 1 to 1.5'. This will serve to greatly reduce the pressure on the levees and on the Old River Control Structure, which as I discussed in my previous post, is America's Achilles' heel, and must be protected. According the National Weather Service, flood heights along the Lower Mississippi from Natchez to New Orleans will peak this week, and slowly fall next week. Rainfall over the next five days is expected to be minimal over the Lower Mississippi watershed. The next chance for significant rain over the region will come Sunday, May 22.


Figure 1. Saturday's opening of the first gate on the Morganza Spillway, as seen on the live feed from USTREAM.

Devastating flooding continues in Colombia
Devastating flooding has hit South America in Colombia, where exceptionally heavy spring rains have killed at least 425 people so far this year, with 482 others missing. Damages are in the billions, and there are 3 million disaster victims. "Some parts of the country have been set back 15 to 20 years", said Plan’s Country Director in Colombia, Gabriela Bucher. "Over the past 10 months we have registered five or six times more rainfall than usual," said the director of Colombia's weather service, Ricardo Lozano. Up to 800 mm (about 32 inches) of rain has fallen along the Pacific coast of Colombia over the past two weeks (Figure 3). The severe spring flooding follows on the heels of the heaviest fall rains in Colombia's History. Weather records go back 42 year in Colombia. Colombia's president Juan Manuel Santos said, "the tragedy the country is going through has no precedents in our history." The 2010 floods killed 571 people--the second deadliest year for floods in Colombian history, next to 1987. The floods did over $1 billion in damage, and affected 2.8 million people. In many places, the flood waters from this great disaster never fully receded, and are now rising again due to this latest round of intense flooding. More rain is in the forecast--the latest forecast from the GFS model calls for an additional 5 - 10 inches (200 - 400 mm) across much of western and northern Colombia in the coming week.


Figure 2. Satellite-observed rainfall over Colombia during the past two weeks shows a region of up to 800 mm (about 32 inches) has fallen near the Pacific coast. Image credit: Navy Research Lab, Monterey.

Colombia's rainy season usually has two peaks: one the fall in October, then then another in the spring in April - May. The heavy rains are due to the presence of the Intertropical Convergence Zone, the area encircling the earth near the Equator where winds originating in the northern and southern hemispheres come together. When these great wind belts come together (or "converge", thus the name "Convergence Zone"), the converging air is forced upwards, since it has nowhere else to go. The rising air fuels strong thunderstorm updrafts, creating a band of very heavy storms capable of causing heavy flooding rains. In La Niña years, when a large region of colder than average water is off the Pacific coast of Colombia, rainfall tends to increase over Colombia. La Niña was moderate to strong during the fall 2010 rains and floods in Colombia, and was largely to blame for Colombia's deadly rainy season. However, in recent months, La Niña has waned. April sea surface temperatures off the Pacific coast of Colombia (0° - 10°N, 85° - 75°W), warmed to the 13th highest temperatures in the past 100 years, 0.68°C above average. Thus, this month's flooding in Colombia may not be due to La Niña.

See also my December 2010 post, Heaviest rains in Colombia's history trigger deadly landslide; 145 dead or missing


Figure 3. Dramatic video of flooding in Colombia over the weekend. Flood waters swept away cars and buses in a busy street in the city of Barranquilla, and passengers climbed on the roofs of their vehicles in order to escape the flood waters. Video credit: BBC.

300-year flood in Canada; wildfires destroy large portions of Slave Lake, Alberta
In Manitoba, Canada, heavy spring snow melt in combination with heavy rains have combined to create record flooding on the Assiniboine River. Authorities intentionally breached a levee over the weekend to save hundreds of homes, but inundated huge areas of farmland as a result. The flood is being called a 300-year flood, and damages are already in excess of $1 billion. In Alberta, Canada, reverse extreme is causing havoc: severe drought and strong spring winds have made ideal conditions for wildfires, which swept into the community of Slave Lake (population 6,700) yesterday. The fires destroyed hundreds of buildings, burning down the town hall and at least 30% of the town, according to preliminary media reports.


Figure 4. Video of the May 15, 2011 Slave Lake fire.

First tropical wave of the year over the Atlantic
The first tropical wave of 2011 is now over the tropical Atlantic near 6°N 46°W, according to the latest Atlantic Tropical Weather Discussion. The wave will bring heavy rain to the northeast coast of South America over the next two days, but is too far south to be a threat to develop into a tropical depression. The Atlantic hurricane season is just two weeks away, and the Eastern Pacific hurricane season began yesterday. So far, the models are not predicting any tropical storm development in the East Pacific or Atlantic over the next six days.

Jeff Masters

Flood

Updated: 8:42 PM GMT on May 16, 2011

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America's Achilles' heel: the Mississippi River's Old River Control Structure

By: JeffMasters, 5:20 PM GMT on May 13, 2011

America has an Achilles' heel. It lies on a quiet, unpopulated stretch of the Mississippi River in Louisiana, a few miles east of the tiny town of Simmesport. Rising up from the flat, wooded west flood plain of the Mississippi River tower four massive concrete and steel structures that would make a Pharaoh envious--the Army Corps' of Engineers greatest work, the billion-dollar Old River Control Structure. This marvel of modern civil engineering has, for fifty years, done what many thought impossible--impose man's will on the Mississippi River. Mark Twain, who captained a Mississippi river boat for many years, wrote in his book Life on the Mississippi, "ten thousand river commissions, with the mines of the world at their back, cannot tame that lawless stream, cannot curb it or define it, cannot say to it "Go here," or Go there, and make it obey; cannot save a shore which it has sentenced; cannot bar its path with an obstruction which it will not tear down, dance over, and laugh at." The great river wants to carve a new path to the Gulf of Mexico; only the Old River Control Structure keeps it at bay. Failure of the Old River Control Structure would be a severe blow to America's economy, interrupting a huge portion of our imports and exports that ship along the Mississippi River. Closure of the Mississippi to shipping would cost $295 million per day, said Gary LaGrange, executive director of the Port of New Orleans, during a news conference Thursday. The structure will receive its most severe test in its history in the coming two weeks, as the Mississippi River's greatest flood on record crests at a level never before seen.


Figure 1. Two views of the Mississippi River. Left: the meander paths of the Mississippi over time, as published in "Geological Investigation of the Alluvial Valley of the Lower Mississippi River" (Fisk, 1944). Right: The Army Corps of Engineers' view of Mississippi River peak flow rates during a maximum 1-in-500 year "Project Flood" (U.S. Army Corp of Engineers, 1958.) The places outlined in red are where the Corps has built flood control structures capable of diverting a portion of the Mississippi's flow.

A better path to the Gulf
The mighty Mississippi River keeps on rollin' along its final 300 miles to the Gulf of Mexico south of New Orleans--but unwillingly. There is a better way to the Gulf--150 miles shorter, and more than twice as steep. This path lies down the Atchafalaya River, which connects to the Mississippi at a point 45 miles north-northwest of Baton Rouge, 300 river miles from the Gulf of Mexico Delta. Each year, the path down the Atchafalaya grows more inviting. As the massive amounts of sediments the Mississippi carries--scoured from fully 41% of the U.S. land area--reach the Gulf of Mexico, the river's path grows longer. This forces it to dump large amounts of sediment hundreds of miles upstream, in order to build its bed higher and maintain the flow rates needed to flush such huge amounts of sediment to the sea. Thus the difference in elevation between the bed of the Mississippi and the Atchafalaya--currently 17 - 19 feet at typical flow rates of the rivers--grows ever steeper, and the path to the Gulf down the Atchafalaya more inviting. Floods like this year's great flood further increase the slope, as flood waters scour out the bed of the Atchafalaya. Without the Old River Control Structure, the Mississippi River would have carved a new path to the Gulf in the 1970s, leaving Baton Rouge and New Orleans stranded on a salt water estuary, with no fresh water to supply their people and industry.

History of the Old River Control Structure
The Mississippi River has been carving a path to the ocean since the time of the dinosaurs, always seeking the shortest and steepest route possible. Approximately once every 1000 years, the river jumps out of its banks and carves a new path. In John McPhee's fantastic essay, The Control of Nature, we learn:

The Mississippi's main channel of three thousand years ago is now the quiet water of Bayou Teche, which mimics the shape of the Mississippi. Along Bayou Teche, on the high ground of ancient natural levees, are Jeanerette, Breaux Bridge, Broussard, Olivier--arcuate strings of Cajun towns. Eight hundred years before the birth of Christ, the channel was captured from the east. It shifted abruptly and flowed in that direction for about a thousand years. In the second century a.d., it was captured again, and taken south, by the now unprepossessing Bayou Lafourche, which, by the year 1000, was losing its hegemony to the river's present course, through the region that would be known as Plaquemines. By the nineteen-fifties, the Mississippi River had advanced so far past New Orleans and out into the Gulf that it was about to shift again, and its offspring Atchafalaya was ready to receive it.

For the Mississippi to make such a change was completely natural, but in the interval since the last shift Europeans had settled beside the river, a nation had developed, and the nation could not afford nature. The consequences of the Atchafalaya's conquest of the Mississippi would include but not be limited to the demise of Baton Rouge and the virtual destruction of New Orleans. With its fresh water gone, its harbor a silt bar, its economy disconnected from inland commerce, New Orleans would turn into New Gomorrah. Moreover, there were so many big industries between the two cities that at night they made the river glow like a worm. As a result of settlement patterns, this reach of the Mississippi had long been known as "the German coast," and now, with B. F. Goodrich, E. I. du Pont, Union Carbide, Reynolds Metals, Shell, Mobil, Texaco, Exxon, Monsanto, Uniroyal, Georgia-Pacific, Hydrocarbon Industries, Vulcan Materials, Nalco Chemical, Freeport Chemical, Dow Chemical, Allied Chemical, Stauffer Chemical, Hooker Chemicals, Rubicon Chemicals, American Petrofina--with an infrastructural concentration equaled in few other places--it was often called "the American Ruhr." The industries were there because of the river. They had come for its navigational convenience and its fresh water. They would not, and could not, linger beside a tidal creek. For nature to take its course was simply unthinkable. The Sixth World War would do less damage to southern Louisiana. Nature, in this place, had become an enemy of the state.


The Atchafalaya steadily took more and more of the Mississippi's water to the Gulf of Mexico during the 20th Century, until by 1950, it had captured 30% of the great river's flow, becoming the 4th largest river in the U.S. by volume discharge. The Army Corps of Engineers stepped in, and in the late 1950s began construction of a massive structure that resembled a dam with gates to control the amount of water escaping from the Mississippi to the Atchafalaya. This "Low Sill Structure", completed in 1963, consisted of a dam with 11 gates, each 44 feet wide, that could be raised or lowered. The entire structure was 566 feet long. A companion "Overbank Structure" was built on dry land next to the Low Sill Structure, in order to control extreme water flows during major floods. The Overbank Structure had 73 bays, each 44 feet wide, and was 3,356 feet long. The total cost of the two structures: about $300 million.


Figure 2. Aerial view of the Mississippi River's Old River Control Structure, looking downstream (south.) Image credit: U.S. Army Corp of Engineers.

The flood of 1973: Old River Control Structure almost fails
For the first ten years after completion of the Old River Control Structure, no major floods tested it, leading the Army Corps to declare, "We harnessed it, straightened it, regularized it, shackled it." But in 1973, a series of heavy snowstorms in the Upper Midwest was followed by exceptionally heavy spring rains in the South. The Mighty Mississippi rose inexorably until the flow rate at the Old River Control Structure reached 2 million cubic feet per second--twenty times the flow of Niagara Falls--and stayed there for more almost three months. Turbulence from the unprecedented flows through the Low Sill Structure scoured the foundation and destroyed a 67-foot-high wing wall that guided water into the structure. Scour holes as big as a football field developed upstream, downstream, and underneath the structure, exposing 50 feet of the 90-foot long steel pilings supporting the structure. The structure began vibrating dangerously, so much so that it would slam open car doors of vehicles parking on top of Highway 15 that crosses over the top. Emergency repairs saved the structure, but it came every close to complete failure.

The flood of 1973 permanently damaged the Low Sill Structure, forcing the Corps to build additional structures to control future great floods. The first of these structures was the Auxilliary Control Structure. This 442-foot long structure, completed in 1986, consisted of six gates, each 62 feet wide, and cost $206 million to build. Joining the mix in the late 1980s was a 192-megawatt hydroelectric power plant, build at a cost of $520 million.


Figure 3. The flow of water in the Mississippi River as of Friday, May 13 (red line) has exceeded 2 million cubic feet per second, and was approaching the all-time record (dashed blue line.) Image credit: USACE.

The Old River Control Structure's greatest test: the flood of 2011
Flow rates of the Mississippi at the latitude of the Old River Control Structure are expected to exceed the all-time record on Saturday, giving the Old River Control Structure its greatest test since the flood of 1973. Since there are now four structures to control the flooding instead of just the two that existed in 1973, the Old River Control Structure should be able to handle a much greater flow of water. The flood of 2011 is not as large as the maximum 1-in-500 year "Project Flood" that the Old River Control Structure was designed to handle, and the Army Corps of Engineers has expressed confidence that the structure can handle the current flood. However, the system has never been tested in these conditions before. This is a dangerous flood, and very high water levels are expected for many weeks. Unexpected flaws in the design of the Old River Control Structure may give it a few percent chance of failure under these sorts of unprecedented conditions. While I expect that the Old River Control Structure will indeed hold back the great flood of 2011, we also need to be concerned about the levees on either side of the structure. The levees near Old River Control Structure range from 71 - 74 feet high, and the flood is expected to crest at 65.5 feet on May 22. This is, in theory, plenty of levee to handle such a flood, but levees subjected to long periods of pressure can and do fail sometimes, and the Corps has to be super-careful to keep all the levees under constant surveillance and quickly move to repair sand boils or piping problems that might develop. Any failure of a levee on the west bank of the Mississippi could allow the river to jump its banks permanently and carve a new path to the Gulf of Mexico. I'll say more about the potential costs of such an event in a future post.

According to the latest information from the Army Corps the Old River Control Structure is currently passing 624,000 cubic feet per second of water, which is 1% beyond what is intended in a maximum "Project Flood." The flow rate of the Mississippi at New Orleans is at 100% of the maximum Project Flood. These are dangerous flow rates, and makes it likely that the Army Corps will open the Morganza Spillway in the next few days to take pressure off of the Old River Control Structure and New Orleans levees. Neither can be allowed to fail. In theory, the Old River Control Structure can be operated at 140% of a Project Flood, since there are now four control structures instead of just the two that existed in 1973 (flows rates of 300,000 cfs, 350,000 cfs, 320,000 cfs, and 170,000 cfs can go through the Low Sill, Auxiliary, Overbank, and Hydroelectric structures, respectively.) Apparently, the Corps is considering this, as evidenced by their Scenario #3 images they posted yesterday. This is a risky proposition, as the Old River Control Structure would be pushed to its absolute limit in this scenario. It would seem a lower risk proposition to open the Morganza spillway to divert up to 600,000 cfs, unless there are concerns the Corps has they aren't telling us about.


Figure 4. Kayaking, anyone? The stilling basin downstream of the Low Sill Structure of the Old River Control Structure, as seen during major flood stage of the Mississippi River on May 10, 2011. The flow rate is 2 - 3 times that of Niagara Falls here. Video by Lee Alessi.

Recommended reading
John McPhee's fantastic essay, The Control of Nature

Jeff Masters

Flood

Updated: 8:57 PM GMT on May 14, 2011

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Mississippi River flood of 2011 already a $2 billion disaster

By: JeffMasters, 12:33 PM GMT on May 12, 2011

The Mississippi River continues to rise to heights never seen before along its course through the states of Mississippi and Louisiana. At Natchez, Mississippi, the river has already hit 59 feet, breaking the previous all-time record of 58 feet set in the great 1937 flood. The river is expected to keep rising at Natchez until May 21, when a crest of 64 feet--a full six feet above the previous all-time record--is expected. Record crests are also expected downstream from Natchez, at Red River Landing and Baton Rouge, Louisiana, on May 22. Fortunately, the levee system on the Lower Mississippi constructed by the Army Corps of Engineers is built to withstand a greater than 1-in-500 year flood, and this flood is "only" a 1-in-100 to 1-in-300 year flood. However, flooding on tributaries feeding into the Mississippi is severe in many locations along the Mississippi, since the tremendous volume of water confined behind the levees is backing up into the tributaries. Huge quantities of farmland are being submerged in the great flood, and damages already exceed $2 billion. Rainfall amounts of at most 1.25 inches are expected over the Lower Mississippi River watershed over the next five days, which should prevent flood heights from rising above the current forecast.


Figure 1. A crowd of hundreds gathered to watch Monday as the Army Corps of Engineers opened gates on the Bonnet Carre' Spillway to allow flood waters from the Mississippi River to flow into Lake Pontchartrain. Image credit: Army Corps of Engineers.

Damage from flood over $2 billion, could hit $4 billion
Damage from the Mississippi River flood of 2011 is already over $2 billion, and could surpass $4 billion. Among the damages so far, as reported by various media sources:

$500 million to agriculture in Arkansas
$320 million in damage to Memphis, Tennessee
$800 million to agriculture in Mississippi
$317 million to agriculture and property in Missouri's Birds Point-New Madrid Spillway
$80 million for the first 30 days of flood fighting efforts in Louisiana

The Mississippi River flood of 2011 now ranks as the 10th costliest flooding disaster in the U.S. since 1980, according to The National Climatic Data Center Billion Dollar Weather Disasters list. The top ten most expensive U.S. flood disasters since 1980 are:

1) $30.2 billion, Summer 1993 Upper Mississippi and Midwest flooding
2) $15.0 billion, June 2008 Midwest flooding
3) $7.5 billion, May 1995 TX/OK/LA/MS flooding
4) $4.8 billion, 1997 North Dakota Red River flood
5) $4.1 billion, Winter 1995 California flooding
6) $4.0 billion, January 1996 Mid-Atlantic and Northeast, blizzard rain and snow melt flooding
7) $3.9 billion, Winter 1996 - 1997 West Coast flooding
8) $2.3 billion, Winter 1982 - 1983 El Niño-related West Coast flooding
9) $2.3 billion, May 2010 Tennessee flood
10) $2 billion, May 2011 Mississippi River flood

With the Morganza Spillway, 35 miles upstream from Baton Rouge, likely to be opened sometime between Friday and Tuesday, hundreds of millions more in damage will occur along the Atchafalaya River basin, which will take up to 300,000 cubic feet per second of water out of the Mississippi and funnel it down to the Gulf of Mexico. About 22,500 people and 11,000 structures will be affected by some flooding, according to Governor Jindal of Louisiana. Also of concern is the impact all the fresh water flows from planned diversions of the Mississippi into salt water oyster beds. According to nola.com, fresh water kills oysters because it wreaks havoc on their metabolism, preventing them from keeping a saltwater balance. Increased fresh water diversions in 2010, used to keep the Deepwater Horizon oil spill away from the coast, contributed to a 50% drop in oyster harvests in 2010 compared to 2009. The huge flow of fertilizer-laden fresh water into the Gulf of Mexico is also expected to create a record-size low-oxygen "dead zone" along the coasts of Louisiana and Texas. This year's dead zone could be as much as 20 percent greater than the record set in 2002, said Louisiana State University marine biologist Eugene Turner in an article published by nola.com. That year, the low oxygen area stretched over 8,500 square miles, an area the size of New Jersey. Dead zones are due to low oxygen level caused by blooms of algae that feed off all the fertilizers washed off of the farms in the Midwest by the Mississippi River.

A record number of billion-dollar weather disasters for so early in the year
The U.S. has already had five weather disasters costing more than a billion dollars this year, which has set a record for the most number of such disasters so early in the year. We've already beat the total for billion-dollar weather disaster for all of 2010 (three), and with hurricane season still to come, this year has a chance of beating 2008's record of nine such disasters. The billion dollar weather disasters of 2011 so far:

1) 2011 Groundhog Day's blizzard ($1 - $4 billion)
2) April 3 -5 Southeast U.S. severe weather outbreak ($2 billion)
3) April 8 - 11 severe weather outbreak ($2.25 billion)
4) April 25 - 28 super tornado outbreak ($3.7 - $5.5 billion)
5) Mississippi River flood of 2011 ($2+ billion)

Losses from the on-going Texas drought and wildfires are already at $180 million, and this is likely to be a billion-dollar disaster by the time all the agricultural losses are tallied.

Good links to follow the flood:
Summary forecast of all crests on Lower Mississippi and Ohio Rivers.
Wundermap for Vicksburg, MS with USGS River overlay turned on.
National Weather Service "May 2011 Mississippi River Flood" web page

Jeff Masters

Updated: 4:44 PM GMT on May 12, 2011

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April 2011: historic U.S. extremes in rains, floods, tornadoes, and fires

By: JeffMasters, 1:40 PM GMT on May 10, 2011

"April was a month of historic climate extremes across much of the United States, including: record breaking precipitation that resulted in historic flooding; recurrent violent weather systems that broke records for tornado and severe weather outbreaks; and wildfire activity that scorched more than twice the area of any April this century." Thus begins the April 2011 climate summary for the U.S. issued yesterday by the National Climatic Data Center. The month featured very cold air spilling southwards from Canada, which gave Washington, Oregon, and Idaho top-ten coldest Aprils. Exceptionally warm air flowing from the Gulf of Mexico, which had its 3rd highest sea surface temperatures on record during April, gave Florida, Louisiana, and Texas top-ten warmest Aprils. The battleground where these two radically different air masses collided featured an exceptionally strong jet stream, which set the stage for the world's two largest tornado outbreaks in history: April 25 - 28 (201 confirmed tornadoes) and April 14 - 16 (155 confirmed tornadoes.) Incredibly heavy rains also resulted, with six states along the Ohio River and Mississippi River watersheds recording their all-time wettest April in history. Eight other states had top-ten wettest Aprils, and the month was the 10th wettest April in U.S. history. Some areas along the Ohio River Valley received up to 20 inches of rain during the month, which is nearly half their normal annual precipitation. April's extreme weather can be blamed in large part on the on-going La Niña episode in the Eastern Pacific. La Niña alters the path of the jet stream, and makes the predominant storm track in winter and spring traverse the regions that saw heavy precipitation. Climate change may have played a role in April's incredible U.S. extreme weather, though a preliminary investigation by NOAA's Climate Science Investigations (CSI) team concluded that "a change in the mean climate properties that are believed to be particularly relevant to severe storms has thus not been detected for April, at least during the last 30 years."


Figure 1. Six states along the Ohio River and Mississippi River watersheds had their all-time wettest April in history during 2011. In contrast, Texas had its 5th driest April on record, after recording its driest March ever. Image credit: National Climatic Data Center.

Great Texas drought of 2011 intensifies
April 2011 was the 5th driest and 5th hottest April in Texas history, going back 117 years. Exceptionally dry conditions have parched the soil and vegetation in Texas, which recorded precipitation of just 1.68 inches (43 mm,) on average, since February 1st. This is easily its driest February-April period on record for the state, nearly an inch less than the previous record (2.56 inches or 65 mm, Feb - Apr 1996.) The six-month period November 2010 - April 2011 was the 2nd driest such period on record. Based on the U.S. Drought Monitor, 94 percent of Texas is in severe to exceptional drought.

As a result of the great drought, an all-time April record of 1.79 million acres of land burned last month in the U.S., mostly in Texas. Much of the fuel for the fires came from dried underbrush and grasses which experienced ideal growing conditions during the summer of 2010, when there was abundant rain across the region. Nation-wide, the year-to-date period, January - April, has the greatest acreage burned in history, according to the National Interagency Fire Center.


Figure 2. The acreage burned in U.S. wildfire in April 2011 was by far the highest in the past decade. Most of the damage was done by a few huge fires. Image credit: National Climatic Data Center.

April 2011 smashes all-time tornado records
The largest tornado outbreak and greatest one-day total for tornadoes in history occurred during the historic April 25 - 28, 2011 tornado outbreak, said NOAA in a press release updated yesterday. They estimate 190 tornadoes touched down during the 24-hour period from 8:00 a.m. EDT April 27 to 8:00 a.m. EDT April 28 (134 tornadoes have already been confirmed, with several weeks of damage surveys still to come.) NOAA's estimate for the number of tornadoes during the three-day April 25 - 28, 2011 Super Outbreak, is 305 (201 are confirmed so far.) This is nearly double the previous record for a multi-day tornado outbreak of 155 tornadoes, set just two weeks previously during the April 14 - 16, 2011 outbreak. There were tornado outbreaks in May 2004 (385 tornadoes) and May 2003 (401 tornadoes) that had more tornadoes, but these outbreaks occurred over an eight-day and eleven-day period, respectively, and were not due to a single storm system. Prior to April 2011, the most tornadoes in a 24-hour period, and in an outbreak lasting less than four days, was the 148 tornadoes in the Super Outbreak of April 3 - 4, 1974. The final tornado count for April 2011 will approach the all-time monthly record of 542 tornadoes, set in May 2003. The previous April record was 267 tornadoes, which occurred in April 1974. The 30-year average for April tornadoes is 135.


Figure 3. The Tuscaloosa-Birmingham tornado of April 27, 2011 killed 65 people and injured over 1000. The tornado carved a path of destruction 80.3 miles (129.2 km) long, and up to 1.5 miles (2.4 km) wide. On May 4, 2011, the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA's Terra satellite observed this segment of the tornado's track, near Birmingham, Alabama. Image credit: NASA Earth Observatory.

The death toll for the epic outbreak continues to fluctuate, and currently stands at 326, with 309 fatalities during the 24-hour-period from 8:00 a.m. April 27 to 8:00 a.m. April 28. The estimated 326 deaths makes this the 4th deadliest tornado outbreak on record. Only the great Tri-State tornado outbreak of 1925 (747 killed), the 1936 Tupelo-Gainsville tornado outbreak (454 killed), and a 1932 outbreak (332 killed) had more deaths.


Figure 4. The Tuscaloosa-Birmingham tornado as it headed toward the Univ. of Alabama on April 27, 2011 (video shot by Chris England, a Univ. of Alabama student).

Mississippi River crests at Memphis: 2nd highest flood on record
The Mississippi River has crested at Memphis, Tennessee this morning, reaching the 2nd highest level on record. The flood height of 47.79' was just below the all-time record height of 48.7' set in the great 1937 flood. Fortunately, the levees constructed by the Army Corps of Engineers are much taller and stronger than was the case 74 years ago, and the mainline Mississippi River levees are expected to hold back this record flood and prevent a multi-billion dollar flood disaster. However, flooding on tributaries feeding into the Mississippi is severe in many locations along the Mississippi, since the tremendous volume of water confined behind the levees is backing up into the tributaries.

Downstream from Memphis, flood waters pouring in from the Arkansas River, Yazoo River, and other tributaries are expected to swell the Mississippi high enough to beat the all-time record at Vicksburg, Mississippi by 1.3' on May 19, by 6' at Natchez, Mississippi on May 21, and by 3.2' at Red River Landing on May 22. The Mississippi is forecast to crest at 19.5' in New Orleans on May 23. The levees in New Orleans protect the city for a flood of 20.0 feet, so it is a good bet that the Army Corps will fully open the Bonnet Carre' Spillway 28 miles upstream from New Orleans this week. The Bonnet Carre' Spillway was partially opened yesterday, and has the capacity to take 250,000 cubic feet per second of Mississippi River water into Lake Pontchartrain. This may not be enough to keep flood heights from rising dangerously close to the top of New Orleans' levees, and the Army Corps may elect to open the final relief valve they have at their disposal--the massive Morganza Spillway, 35 miles upstream from Baton Rouge. The Morganza Spillway has been opened only once in history, back in 1973. Rainfall amounts of at most 0.75 inches are expected over the Lower Mississippi River watershed over the next five days, which should prevent flood heights from rising above the current forecast.

Good links to follow the flood:
Summary forecast of all crests on Lower Mississippi and Ohio Rivers.
Wundermap for Vicksburg, MS with USGS River overlay turned on.
National Weather Service "May 2011 Mississippi River Flood" web page

Jeff Masters

Flood Climate Summaries

Updated: 7:37 PM GMT on May 10, 2011

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Mississippi River sets all-time flood records; 2nd major spillway opens

By: JeffMasters, 2:06 PM GMT on May 09, 2011

The Mighty Mississippi continues to wreak havoc as the river's highest flood crest in history pushes southwards near Memphis, Tennessee today. The river crested at its highest height on record over the past four days along a 70-mile stretch from New Madrid, Missouri to Tiptonville, Tennessee, to Caruthersville, Missouri, smashing records that had stood since the great flood of 1937. The flood height of 47.6' at Caruthersville, Missouri, on Saturday was a full 1.6 feet above the previous record flood height, set in 1937. However, thanks in part to decision by the Army Corps of Engineers last Monday to intentionally destroy a levee at Birds Point on the west bank of the Mississippi, pressure on the levees along this stretch of river was substantially reduced, potentially preventing multi-billion-dollar levee breaches. Currently, the Mississippi is expected to reach its 2nd highest level on record at Memphis on May 10, cresting at 48.0'. The all-time record at Memphis occurred during the great flood of 1937, when the river hit 48.7'. Downstream from Memphis, flood waters pouring in from the Arkansas River, Yazoo River, and other tributaries are expected to swell the Mississippi high enough to beat the all-time record at Vicksburg, Mississippi by 1.3' on May 19, and smash the all-time record at Natchez, Mississippi by six feet on May 21, and by 3.2 feet at Red River Landing on May 22. Red River Landing is the site of the Old River Control Structure, the Army Corps' massive engineering structure that keeps the Mississippi River from carving a new path to the Gulf of Mexico. I'll have a detailed post talking about the Old River Control Structure later this week. Its failure would be a serious blow to the U.S. economy, and the great Mississippi flood of 2011 will give the Old River Control Structure its most severe test ever. Also of concern is the forecast for the Mississippi to crest at 19.5 feet in New Orleans on May 23. The levees in New Orleans protect the city for a flood of 20.0 feet--that is not much breathing room. Fortunately, rainfall of at most 0.5 inches is expected over the Lower Mississippi River watershed over the next five days, which should prevent flood heights from rising above the current forecast.


Figure 1. Opening of the Bonnet Carre' Spillway on March 17, 1997. The spillway was operational from March 17 to April 18, 1997, operating at a maximum flow of 243,000 cu ft/s (6,900 m3/s). Image credit: Army Corps of Engineers.

Bonnet Carre' Spillway opens
Today, the Army Corps of Engineers is setting in motion another key part of their plan to control the great flood of 2011. The Corps is opening the Bonnet Carre' Spillway to divert 250,000 cubic feet per second of water from the Mississippi River into Lake Pontchartrain, some 28 miles upstream from New Orleans. A large crane will traverse a 1.5 mile-long stretch of the Mississippi River and remove large wooden slats that will allow the river to spill northwards into a 6-mile long channel lined by guide levees, to Lake Pontchartrain. The land that will be inundated is uninhabited and is not farmed, unlike the land of the Birds Point-New Madrid Spillway that was inundated by last week's intentional levee breach. The main concern with opening the Bonnet Carre' Spillway is the impact of the Mississippi River's fresh water on the salt water ecosystems of Lake Pontchartrain. This is the 10th time since 1937 that the Bonnet Carre' Spillway has been opened. The Army Corps is considering opening the final spillway they have in reserve, the great Morganza Spillway in Louisiana, late this week. The Army Corps has never opened all three Lower Mississippi River spillways at the same time. The Morganza Spillway has been opened only once, back in 1973.


Figure 2. The last time the Bonnet Carre Spillway was opened was in 2008. The International Space Station captured this image of the muddy brown waters of the Mississippi flooding into Louisiana's Lake Pontchartrain, just upstream from New Orleans. Image credit: NASA Earth Observatory.

Good links to follow the flood:
Summary forecast of all crests on Lower Mississippi and Ohio Rivers.
Wundermap for Cairo, IL with USGS River overlay turned on.
National Weather Service "May 2011 Mississippi River Flood" web page

Jeff Masters

Flood

Updated: 6:01 PM GMT on May 09, 2011

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Record floods on Mississippi River, Lake Champlain; 3rd EF-5 tornado verified

By: JeffMasters, 3:40 PM GMT on May 06, 2011

The Ohio River at Cairo, Illinois continues to fall today, with a level of 59.3', 2.5' below the all-time peak of 61.8' set on Monday night. On Monday night, the Army Corps of Engineers was forced to intentionally destroy a levee at Birds Point on the west bank of the Mississippi, just downstream from Cairo, Illinois, in order to relieve pressure on the levees in Cairo and save that city from a billion-dollar levee breach. The destruction of the Birds Point levee also helped slow the rise of the Mississippi River just south of its confluence with the Ohio River, but the river is still rising slowly, and has now set all-time records at New Madrid, Missouri, Tiptonville, Tennessee, and Caruthersville, Missouri--a 70-mile stretch of river downstream from Cairo. Currently, the Mississippi is expected to reach its 2nd highest level on record at Memphis on May 10, cresting at 48.0'. The all-time record at Memphis occurred during the great flood of 1937, when the river hit 48.7'. Downstream from Memphis, flood waters pouring in from the Arkansas River, Yazoo River, and other tributaries are expected to swell the Mississippi high enough to beat the all-time record at Vicksburg, Mississippi by 1.3' on May 20, and smash the all-time record at Natchez, Mississippi by six feet on May 22, and by 3.2 feet at Red River Landing on May 23. Red River Landing is the site of the Old River Control Structure, the Army Corps' massive engineering structure that keeps the Mississippi River from carving a new path to the Gulf of Mexico. I'll have a detailed post talking about the Old River Control Structure next week. Its failure would be a serious blow to the U.S. economy, and the great Mississippi flood of 2011 will give the Old River Control Structure its most severe test ever. Also of concern is the forecast for the Mississippi to crest at 19.5 feet in New Orleans on May 24. The levees in New Orleans protect the city for a flood of 20.0 feet--that is not much breathing room. Fortunately, only 0.5 - 1.5 inches of rain are expected over the Missouri/Illinois region over the next five days, which should not raise flood heights significantly.

Good links to follow the flood:
Summary forecast of all crests on Lower Mississippi and Ohio Rivers.
Wundermap for Cairo, IL with USGS River overlay turned on.
National Weather Service "May 2011 Mississippi River Flood" web page


Figure 1. Flooding of the farmland along the Birds Point-New Madrid Floodway due to the intentional destruction of a levee along the west bank of the Mississippi River in Southeast Missouri is obvious in this pair of before and after photos. Image credit: NASA Earth Observatory.

Lake Champlain hits highest level since 1869; record flooding in Canada
The Governor of Vermont declared a state of emergency yesterday in Vermont due to flooding along Lake Champlain. Heavy rains over the past ten days, combined with snow melt have combined to push the lake ot three feet above flood stage, and the lake has now broken its previous record high, set in 1869. The flooding has caused numerous road closures but no evacuations in the U.S. The story is different in Quebec, Canada, where flood waters from Lake Champlain coursing down the Richelieu River have created a 150-year flood, forcing the evacuation of 1,000 people and the flooding of 3,000 homes and businesses in the Richelieu Valley, just south of Montreal. The lake level is expected to crest Saturday morning, then slowly fall. Lake Champlain is 120 miles long with nearly 600 miles of shoreline, making it the sixth largest natural lake in the U.S., trailing only the Great Lakes in size.


Figure 2. Five to eight inches of precipitation has fallen over much of the Lake Champlain watershed over the past two weeks. Image credit: NOAA/AHPS.

A third tornado from the April 27 Super Outbreak rated an EF-5
Yesterday, the Jackson, Mississippi office of the NWS upgraded the violent tornado that hit Neshoba, Kemper, Winston, and Noxubee Counties in the northeast part of the state to EF-5 status, with top winds of 205 mph. This tornado continued into Alabama and had a total path length of 92.3 miles. Three people died in the tornado, which was so powerful that it dug out the ground to a depth of two feet over an area 25 - 50 yards wide and several hundred yards long. This is the third tornado rated EF-5 from the April 27 outbreak; tornadoes that hit Smithville, MS and Hackleburg, AL also received EF-5 ratings.


Figure 3. EF-5 damage from the April 27, 2011 Neshoba tornado in Mississippi. The tornado was so powerful that it dug out the ground to a depth of two feet over an area 25 - 50 yards wide and several hundred yards long. Image credit: NWS.

Rare EF-2 tornado hits New Zealand
A tornado ripped through New Zealand's largest city, Auckland, on Tuesday, killing one person at a shopping mall and injuring at least fourteen others. The damage was rated EF-2, making the tornado one of the strongest in New Zealand's history. Below is some footage of the twister, showing why it is dangerous to be in a car during a tornado. (Note also the clockwise rotation of the tornado--this is the Southern Hemisphere, where storms rotate clockwise.)


Figure 4. Footage of the May 3, 2011 New Zealand tornado that passed through the Auckland suburb of Albany.

I'll have a new post Monday.

Jeff Masters

Flood Tornado

Updated: 5:58 PM GMT on May 09, 2011

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April's tornado outbreaks the two largest in history

By: JeffMasters, 2:54 PM GMT on May 05, 2011

The largest tornado outbreak and greatest one-day total for tornadoes in history occurred during last week's historic super tornado outbreak, said NOAA in a press release on Wednesday. They estimate 190 tornadoes touched down during the 24-hour period from 8:00 a.m. EDT April 27 to 8:00 a.m. EDT April 28 (132 tornadoes have already been confirmed, with several weeks of damage surveys still to come.) NOAA's estimate for the number of tornadoes during the three-day April 25 - 28, 2011 Super Outbreak, is 305. This is nearly double the previous record for a multi-day tornado outbreak of 155 tornadoes, set just two weeks previously during the April 14 - 16, 2011 outbreak. There were tornado outbreaks in May 2004 (385 tornadoes) and May 2003 (401 tornadoes) that had more tornadoes, but these outbreaks occurred over an eight-day and eleven-day period, respectively, and were not due to a single storm system. Prior to April 2011, the most tornadoes in a 24-hour period, and in an outbreak lasting less than four days, was the 148 tornadoes in the Super Outbreak of April 3 - 4, 1974.



Figure 1. A truly frightening radar image: multiple hook echoes from at least ten supercell thunderstorms cover Mississippi, Alabama, and Tennessee during the height of the April 27, 2011 Super Outbreak. A multi-hour animation is available here.



Figure 2. Preliminary tornado tracks from NWS survets for the April 27, 2011 tornado outbreak. Image credit: NWS Southern Region.

The death toll for the epic outbreak continues to fluctuate, and has decreased substantially to 318. The count decreased in Alabama from 250 to 236 due to some of the victims being counted twice. There are still hundreds of people missing from the tornado, and search teams have not yet made it to all of the towns ravaged by the tornadoes. The estimated 318 deaths makes this is the 4th or 5th deadliest tornado outbreak on record. Only the great Tri-State tornado outbreak of 1925 (747 killed), the 1936 Tupelo-Gainsville tornado outbreak (454 killed), and a 1932 outbreak (332 killed) had more deaths.

Other notable facts from the great April 25 -28, 2011 tornado outbreak
The Tuscaloosa-Birmingham tornado is likely to be the most expensive tornado of all-time, and damage from the April 25 - 28 outbreak is the most expensive tornado outbreak in history. Insured damages have been rated at $2 - $5 billion, and uninsured losses will be several billion more. The previous most expensive tornado outbreak in history was the $3.5 billion price tag, in 2005 dollars, of the April 3 - 4, 1974 Super Outbreak .

The Tuscaloosa-Birmingham tornado caused at least 65 fatalities. This tornado had a maximum width of 1.5 miles and a track 80 miles long. These are the most fatalities from a single tornado in the United States since May 25, 1955, when 80 people were killed in a tornado in southern Kansas with 75 of those deaths in Udall, Kansas.

NOAA estimates there were more than 600 tornadoes during the month of April 2011, shattering previous records. The previous April tornado record was 267, set in 1974. April has averaged just 161 tornadoes over the past decade. The previous record number of tornadoes during any month was 542, set in May 2003. So far there have been an estimated 881 tornadoes in 2011. The annual tornado record is 1,817, set in 2004. May is historically the most active month for tornadoes.

So far, 2011 is the 13th deadliest year for tornadoes on record with 369, and the deadliest year since the advent of Doppler radar in late 1980s and 1990s. The deadliest year on record is 1925 with 794.

The outbreak had fourteen violent tornadoes--two EF-5s (the Smithville, MS tornado, and the Hackleburg, AL tornado), and twelve EF-4s. The Super Outbreak of 1974 had far more violent tornadoes, with an unprecedented seven F5s and 23 F4s.

National Weather Service forecast offices provided plenty of warning for the tornadoes, issuing life-saving tornado warnings with an average lead-time of 24 minutes. Warnings were in effect for more than 90 percent of the tornadoes.


Figure 3. Youtube video of the Tuscaloosa-Birmingham tornado of April 27, 2011, as it hit Birmingham.

The most violent tornado of the outbreak: the 210-mph Hackleburg tornado
The most violent and longest-lived tornado of the great April 26 - 28, 2011 outbreak was the Hackleburg tornado. This tornado initially touched down in Northwest Alabama near the Mississippi border, then roared to the northeast for 132.1 miles into Tennessee, causing EF-5 damage at many locations along its path. The most significant damage occurred in the town of Phil Campbell, wind in excess of 200 mph sucked up a 25-foot section of pavement and scattered it up to 1/3 mile away. Tornadoes that can suck up pavement are a rare breed, earning this twister its EF-5 rating. The tornado intensified even further as it hit the town of Oak Grove, where winds estimated at 210 mph over a swath more than one mile wide completely destroyed many buildings, tossed a Corvette 641 feet, and tossed another large car so far that it has not yet been found.

A list of the pages at each National Weather Service forecast office on the tornadoes from the April 25 - 28 outbreak that affected their area (posted by wunderground member beell, thanks!):

Birmingham, AL
Huntsville, AL
Mobile, AL
Little Rock, AR
Tallahasse, FL
Atlanta, GA
Louisville, KY
Paducah, KY
Shreveport, LA
Jackson, MS
Albany, NY
Binghamton, NY
Wilmington, OH
State College, PA
Columbia, SC
Greenville, SC
Memphis, TN
Morristown, TN
Nashville, TN
Dallas, TX
Blacksburg, VA
Sterling, VA
Wakefield, VA

All-time Mississippi River flood records fall
This week, for the first time in 74 years, the Army Corps of Engineers was forced to intentionally destroy the Birds Point levee on the west bank of the Mississippi River, just downstream from the river's confluence with the Ohio River at Cairo, Illinois. The Ohio River at Cairo, Illinois continues to fall this morning, thanks to this emergency operation, with a level two feet below the all-time peak of 61.8' set on Monday night. The destruction of the Birds Point levee also helped slow the rise of the Mississippi River just south of its confluence with the Ohio River, but the river is still rising slowly, and has now set all-time records at New Madrid, Missouri, Tiptonville, Tennessee, and Caruthersville, Missouri--a 70-mile stretch of river downstream from Cairo. The massive pulse of flood waters will continue downstream for the next 2 - 3 weeks, setting all-time flood records at many locations. The National Weather Service in Jackson, Mississippi has created a nice "May 2011 Mississippi River Flood" web page that details the current stages, expected crests, and previous record crests along the river's path. Currently, the Mississippi is expected to reach its 2nd highest level on record at Memphis on May 11, beat the all-time record at Vicksburg, Mississippi by 1.3' on May 20, and smash the all-time record at Natchez, Mississippi by six feet on May 22. I'll be saying much more about this unprecedented Mississippi flood on Friday, and throughout the month of May.


Figure 4. The Portlight relief trailer being loaded in Summerville, SC, in preparation for a journey to the tornado disaster zone.

Helping out tornado victims
For those who want to lend a helping hand to those impacted by the widespread destruction this month's severe weather has brought, stop by the portlight.org blog. They have been very active in this disaster, bringing aid to many of the victims of this great tragedy.

Jeff Masters

Tornado

Updated: 8:21 PM GMT on October 24, 2011

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Army Corps blows up levee to help fight unprecedented Mississippi River flood

By: JeffMasters, 4:47 PM GMT on May 03, 2011

A brilliant string of explosions rippled across a two-mile length of the Mississippi River levee at Birds Point, Missouri at 10pm last night. As the levee disintegrated, a massive cascade of muddy brown water from the Father of Waters gushed into the crevasse, thundering with the flow of eight Niagara Falls. The waters quickly spread out over 133,000 acres of rich farmland, rushing southwards along the 35-mile long Birds Point-New Madrid Spillway. The levee that was destroyed--called a plug fuse levee--was designed to be destroyed in the event of a record flood. In a marathon 20-hour operation, 150 engineers from the Army Corps of Engineers packed 22 wells in the levee with explosives on Sunday and Monday. A raging thunderstorm with dangerous lightning halted the work for a time on Sunday night, as the engineers were pulled off the levee due to concerns about lightning. Final approval for the demolition occurred after a series of failed court challenges, brought by the Attorney General of Missouri, ended at the Supreme Court on Monday. Damage to the farmland and structures along the the Birds Point-New Madrid Spillway is estimated to cost $317 million due to the intentional breach of the levee. The fact that the Army Corps is intentionally causing 1/3 of billion dollars in damage is stark evidence of just how serious this flood is. The Birds Point levee has been demolished only once before, during the historic 1937 flood.


Figure 1. Still frame from an Army Corps of Engineers video of last night's demolition of the Birds Point levee on the Mississippi River.


Figure 2. The gauge on the Ohio River at Cairo was at record highs over the past few days, but the river level is now falling, thanks to the demolition of the Birds Point levee.

Unprecedented flooding on the Ohio and Mississippi Rivers
Snow melt from this winter's record snow pack across the Upper Mississippi River has formed a pulse of flood waters that is moving downstream on the Mississippi. This pulse of flood waters passed St. Louis on Saturday, where the river is now falling. The snow melt pulse arrived on Monday at Thebes, Illinois, about 20 miles upstream from the Mississippi/Ohio River junction at Cairo. The Mississippi River crested yesterday at Thebes at 45.52', which beats 1993 as the 2nd highest Mississippi River flood of all-time at Thebes. This floodwater pulse is headed south to Cairo, Illinois, and will join with the record water flow coming out of the Ohio River to create the highest flood heights ever recorded on a long stretch of the Mississippi, according to the latest forecasts from the National Weather Service. Along a 400-mile stretch of the Mississippi, from Cairo to Natchez, Mississippi the Mississippi is expected to experience the highest flood heights since records began over a century ago at 5 of the 10 gauges on the river. Areas that are not protected by levees can expect extensive damage from the flooding, but the mainline levees on the Lower Mississippi are high enough so that the flood waters are predicted to stay at least 3 feet below the tops of the levees.

The Mississippi River at New Madrid, MO, about 40 miles downstream of the confluence of the Mississippi and Ohio Rivers, crested at 46.54' this morning, the 2nd highest flood in history. The river is now falling, thanks to the blowing of the Birds Point levee. Rains of up to ten inches over the past three days in the region have now ended, but this water will enter the river system over the next few days, increasing heights on the river once again. The Mississippi is predicted to rise to 50 feet late this week, two feet above the all-time record height of 48 feet. The NWS warns that at this height, "Large amounts of property damage can be expected. Evacuation of many homes and businesses becomes necessary." Previous record heights at this location:

(1) 48.00 ft on 02/03/1937
(2) 46+ ft on 05/03/2011
(2) 44.60 ft on 04/09/1913
(3) 43.60 ft on 04/04/1975
(4) 43.50 ft on 02/16/1950
(5) 42.94 ft on 03/17/1997


Figure 3. Radar-estimated rainfall near the confluence of the Ohio and Mississippi Rivers totaled 4 - 10 inches over a wide area during the past three days.


Figure 3. Flooding on the Mississippi in Missouri at the end of April. Image credit: USACE.

The "Project Flood"
The levees on the Lower Mississippi River are meant to withstand a "Project Flood"--the type of flood the Army Corps of Engineers believes is the maximum flood that could occur on the river, equivalent to a 1-in-500 year flood. The Project Flood was conceived in the wake of the greatest natural disaster in American history, the great 1927 Mississippi River flood. Since the great 1927 flood, there has never been a Project Flood on the Lower Mississippi, downstream from the confluence with the Ohio River (there was a 500-year flood on the Upper Mississippi in 1993, though.) On Sunday, Major General Michael Walsh of the Army Corps of Engineers, President of the Mississippi Valley Commission, the organization entrusted to make flood control decisions on the Mississippi, stated: "The Project Flood is upon us. This is the flood that engineers envisioned following the 1927 flood. It is testing the system like never before."

At Cairo, the project flood is estimated at 2.36 million cubic feet per second (cfs). The current prediction for the flow rate at New Madrid, the Mississippi River gauge just downstream from Cairo, is 1.89 million cfs on May 7, so this flood is not expected to be a 1-in-500 year Project Flood. In theory, the levee system is designed to withstand this flood. But the Army Corps is in for the flood fight of its life, and it will be a long a difficult few weeks. Here's how Major General Michael Walsh of the Army Corps of Engineers described his decision yesterday to blow up the Birds Point levee:

"Everyone I have talked with--from boat operators, to labors, scientist and engineers, and truck drivers have all said the same thing--I never thought I would see the day that the river would reach these levels.

We have exceeded the record stage already at Cairo. We are on a course to break records at many points as the crest moves through the system. Sometimes people celebrate with "records"--but not this time. Making this decision is not easy or hard--it's simply grave-- because the decision leads to loss of property and livelihood--either in a floodway--or in an area that was not designed to flood. The state of Missouri has done a superb job of helping people escape the ravages of water in the floodway. But other places--not designed to flood have had no warning if their areas succumb to the pressures of this historic chocolate tide.

I spent last night on the river...lashed to an anchor barge in the current near the top of the floodway. The rains continued to pound the deck of the Motor Vessel. The cold winds moved us around--and the current and water levels kept increasing as the rain storms continue to grow over the Ar/Miss/Ohio/TN Watershed.

So, with the tool that has withstood many tests: the test of operation in 1937; decades of challenges that resulted in the 1986 Operation Plan; reviews and numerous unsuccessful court challenges--I have to use this tool. I have to activate this floodway to help capture a significant percentage of the flow.

I don't have to like it but we must use everything we have in our possession, in the system to prevent a more catastrophic event. So, today, I give the order to operate the Floodway."



Jeff Masters

Flood

Updated: 4:39 PM GMT on May 04, 2011

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Two EF-5 tornadoes confirmed from last week's outbreak; record Ohio River flood

By: JeffMasters, 1:23 PM GMT on May 02, 2011

Damage surveys and the hunt for missing victims continues today in the areas devastated by last week's historic tornado outbreak. With the death toll in the 340 - 350 range, the April 25 - 28 tornado outbreak has surpassed the April 3 - 4, 1974 Super Outbreak (315 killed) as the deadliest U.S. tornado outbreak of the past 50 years. Hardest hit was Alabama, with 249 deaths; Tennessee and Mississippi had 34 deaths each, and deaths were also reported in Arkansas, Georgia, Virginia, Louisiana, and Ontario, Canada. Twenty-eight separate tornadoes killed people. According wunderground's weather historian, Christopher C. Burt, in his post The World's Deadliest Tornadoes, only the death toll of the great Tri-State tornado outbreak of 1925 (747 killed) and the 1936 Tupelo-Gainsville tornado outbreak (454 killed) were greater. These outbreaks both occurred during an era before Doppler radar and tornado warnings. Had last week's outbreak occurred back in those days, I expect the death toll would have been in the thousands. The National Weather Service provided warning times of 15 - 30 minutes for all of last week's killer storms, allowing time for most people to get to safe shelters.


Figure 1. MODIS satellite image from NASA's Aqua satellite taken on Friday, April 29, 2011, showing the damage paths of three of Wednesday's tornadoes in Alabama.


Figure 2. Damage paths of Wednesday's tornadoes as compiled by the National Weather Service office in Birmingham, Alabama.

Damage surveys will continue for another week, so it is uncertain exactly how many tornadoes were spawned in last week's outbreak. The confirmed count is already at 146, which would make it the 4th largest tornado outbreak in history. The total is likely to surpass the 155 confirmed tornadoes logged during the April 14 - 16, 2011 tornado outbreak. According to a list of tornado outbreaks maintained by Wikipedia, only two other tornado outbreaks have had as many as 150 twisters--the May 2004 outbreak (385), and the May 2003 outbreak (401). So, remarkably, two of the top four outbreaks in history occurred within two weeks of each other. In addition, the period from 8am April 27 - 8am April 28 during last week's outbreak has a good chance of breaking the record for most tornadoes in a 24-hour period, which is currently 148 (set in the April 3 - 4, 1974 Super Outbreak.)

Two EF-5 tornadoes confirmed
Damage surveys have confirmed that last week's April 25 - 28 outbreak spawned at least eleven violent EF-4 tornadoes (winds 166 - 200 mph) and two EF-5 tornadoes (winds greater than 200 mph.) This is only the 5th time since tornado ratings began in 1950 that two top-end tornadoes have occurred on the same day. The last time was on March 13, 1990 in Kansas. An EF-5 with 205 mph winds hit Smithville, Mississippi at 3:44pm EDT on Wednesday. The tornado's path was only 3 miles long, but was 1/2 miles wide and did extreme damage. Fifteen were killed, 40 injured, and 166 buildings destroyed. Some well-built modern 2-story homes that were bolted to their foundations were completely destroyed, leaving only the foundation. This type of damage is characteristic of an EF-5 tornado with 205 mph winds. The Smithville tornado is the first EF-5 tornado in Mississippi since the Candlestick Park tornado of March 3, 1966. The other EF-5 tornado of the day, the Hackleburg tornado, touched down in Northwest Alabama in Marion County at 3pm CDT, and devastated the towns of Phil Campbell and Hackleburg. This tornado killed at least 25 people. Meteorologist Gary Dobbs, with WAAY-TV since 1984, spotted this tornado from his car and was unable to get to his storm shelter. While his house was destroyed around him, Dobbs was thrown 40 feet from the house. The door of the storm shelter blew off, and none of the friends therein were seriously injured. Dobbs required hospitalization. One other tornado that may get an EF-5 rating is the violent Tuscaloosa/Birmingham tornado, which killed at least 66 people and injured over 1000. It was the deadliest tornado in the U.S. since 1955, when 80 people died in Udall, Kansas. This tornado had a path length of 80.3 miles, and has been preliminarily rated at high-end EF-4 with 190 mph winds. The Tuscaloosa-Birmingham tornado is likely to be the most expensive tornado of all-time, and damage from the April 25 - 28 outbreak is likely rank as the most expensive tornado outbreak in history. Insured damages have been rated at $2 - $5 billion, and uninsured losses will be several billion more. The previous most expensive tornado outbreak in history was the $3.5 billion price tag, in 2005 dollars, of the April 3 - 4, 1974 Super Outbreak .


Figure 3. Radar reflectivity image of the Hackleburg, Alabama tornado of April 27, 2011, a few minutes after it devastated the town of Hackleburg, Alabama (white cross at center of image.) The Hackleburg tornado was rated an EF-5 with greater than 200 mph winds.


Figure 4. Remarkable video of the tornado that hit Tuscaloosa, Alabama. Beginning at about 2:30 into the video, one can see the ominous mini-vorticies and cloud of debris that encircled the tornado.

Unprecedented flooding on Ohio River
Last week's storm system, in combination with heavy rains earlier this month and over past 24 hours, pushed the Ohio River at Cairo, Illinois to 60.6 feet at 1am CDT May 1. This is the highest flood in history, besting the 59.5' mark of 1937. Additional heavy rains of 2 - 4 inches are expected over the next five days, and the river is not expected to crest until Wednesday, at a height of 61.5 feet. As the record flood waters from the Ohio River pour into the Mississippi and are joined by melt water from the this winter's record snow pack over the Upper Mississippi, all-time flood heights are likely to be exceeded at many points along a 400-mile stretch of the Mississippi below its confluence with the Ohio. I'll have a more detailed look in my next post.

Jeff Masters

Flood Tornado

Updated: 2:04 AM GMT on May 03, 2011

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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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