Weather Extremes

Death Valley ‘Sliding Rocks’ Mystery Resolved

By: weatherhistorian, 7:21 PM GMT on August 29, 2014

Death Valley ‘Sliding Rocks’ Mystery Resolved

An article published in the science journal PLOS ONE on August 27th by scientists from the Scripps Institution of Oceanography has finally put to rest the mystery of the ‘sliding’ rocks of Racetrack Playa in Death Valley.

One of the many rocks photographed that seemed to have slid across Racetrack Playa in Death Valley. The phenomenon was first noticed in the 1940s. Many hypotheses have been made as to the cause of the phenomenon, including that perhaps it is an elaborate hoax. Racetrack Playa is located in the northwestern portion of Death Valley National Park and rests at an elevation of 3,708’ (1,130 m). Photo by Meera Dolasia and taken in 2009.

For years people have been mystified by the apparent movement of rocks, some weighing over 100 pounds, over hundreds of feet along the flat surface of Racetrack Playa in Death Valley leaving long tracks etched in the ground as they move. Richard D. Norris and his cousin James M. Norris launched an investigation into the mystery beginning in 2011 with their ‘Slithering Stones Research Initiative’ sponsored by NASA and Scripps among others. They established a weather station in the area near the playa (with permission from the Death Valley National Park Service, not an easy accomplishment!) and placed 15 stones attached with GPS tracking units in the vicinity of the existing ‘sliding stones’ that first triggered the mystery.

Location of weather station in Death Valley overlooking the GPS-instrumented rock zone on Racetrack Playa. Map from PLOS ONE article.

One of the GPS-instrumented rocks and its track across the playa. The GPS unit, with its battery pack, was placed in a cavity bored into the top of the rock. Photo from PLOS ONE article.

Using time-lapse photography they caught on camera the rocks sliding across the playa at the surprisingly fast pace of up to 15 feet (3-5 meters) per minute on December 4th and December 20th, 2013 as well as other occasions. In all cases rainfall preceded the events, which froze just beneath the playa surface. During the mornings after the rainfalls and freeze-up they relate what happened:

” Steady light winds and morning sun caused floating ice to break-up near mid day, accompanied by widespread popping sounds from fragmenting ice panels. Ice initially broke into floating panels tens of meters in size that became increasingly fragmented and separated by open rippled water as melting continued. Floating ice sheets driven by wind stress and flowing water, pushed rocks resting on the playa surface, in some cases moving >60 rocks in a single event...Two rocks recorded movements on December 4; one trail was 65.6 m long (stone mass 16.6 kg) and the other of 64.1 m (stone mass 8.2 kg). Both movements lasted 16 minutes starting at 11:05 am local time. These rocks were originally located ~153 meters apart, and began motion within 6 seconds of each other. Both rocks initially reached velocities of 5–6 m/minute that fell to 3–4 m/minute by 6 minutes into the move event. The December 20 event is recorded by one rock (stone mass 15.4 kg) with a 39.1 m movement over 12.3 minutes starting at 11:37 am. The rock initially achieved a velocity of 2–3 m/minute, then nearly stopped 4 minutes into the move, resumed a minute later, and traveled 5 m/minute to the end of the move event.”

Graphic of weather conditions measured at the weather station established just above the play for the period of November 19, 2013-January 9, 2014. At the top of the graph are the dates of major rock movements. From PLOS ONE article.

An overview photo (from the ‘Source Hill’ shown in the map earlier) displaying the dozens of GPS-instrumented rocks that slid across the playa on December 20, 2013. Photo from PLOS ONE article.

Although this hypothesis has been made before (along with many others) this is the first time peer-reviewed proof of the phenomenon and what causes it has been confirmed by scientific investigation.

The entire article in PLOS ONE (a fascinating read) may be found here.

REFERENCE: ‘Sliding Rocks on Racetrack Playa, Death Valley National Park: First Observation of Rocks in Motion’ by Richard D. Norris, James M. Norris, Ralph D. Lorenz, Jib Ray, Brian Jackson, PLOS ONE, August 27, 2014.

Christopher C. Burt
Weather Historian

Extreme Weather Mysteries

Updated: 1:28 AM GMT on September 02, 2014


Record Warmth in Northeastern Canada, Record Cold in Northern Ireland

By: weatherhistorian, 7:55 PM GMT on August 26, 2014

Record Warmth in Northeastern Canada, Record Cold in Northern Ireland

August has continued the July pattern of anomalously warm weather in Canada’s far eastern regions with a new all-time record high of 22.7°C (72.9°F) measured at Resolution Island, Nunavut on August 23rd. In contrast, Northern Ireland observed its coldest August temperature on record the morning of August 24th with a -1.9°C (28.6°F) reading.

Resolution Island (61° 36’N, 64° 38’W) is located in the normally icy Hudson Strait between the southern tip of Baffin Island and northern tip of Labrador, Newfoundland. The weather this summer has been abnormally warm in the Baffin Island and Newfoundland region in contrast to the cooler than normal conditions in western Quebec, Ontario, and the central U.S. In fact, the maximum temperature at St. John, Newfoundland during July was 0.4°C (0.7°F) warmer than the maximum observed in Toronto (City Center site) over the course of the entire month!

500 mb heights and anomalies for North America during July. Note the anomalous warmth centered over Newfoundland Island and Baffin Island. NOAA data.

St. John, the capital city of Newfoundland, enjoyed its warmest July on record with an average temperature of 20.0°C (68.0°F), some 4.2°C (7.6°F) above the normal July average of 15.8°C (60.4°F). According to local news reports, the previous July monthly record was 18.6°C (65.5°F) set during July 1874. On July 30th the temperature peaked at 29.5°C (85.1°F) short of their all-time record of 31.5°C (88.7°F) observed on July 6, 1983. So far, this August has averaged 17.0°C (62.6°F), 0.9°C (1.6°F) above the normal of 16.1°C (61.0°F).

St. John’s daily climate data for this past July. Note all the 25°C (77°F) plus days. The normal daily maximum temperature during July is 20.7°C (69.3°F) and the normal low 10.9°C (51.6°F). Table from Environment Canada.

Meanwhile, on the other side of the Atlantic, Northern Ireland recorded its coldest August temperature on record when a reading of -1.9°C (28.6°F) was measured at Katesbridge, County Down on the morning of August 24th. The previous record was -1.1°C (30.0°F) observed at Loughermore Forest in August 1964. The coldest August temperature on record for all of the U.K. is -4.3°C (24.3°F) at Lagganlia, Scotland on August 21, 1973 (this excludes high-elevation sites such as Ben Nevis Observatory or Cairngorm).

KUDOS: Thanks to Maximiliano Herrera for Resolution Island data and bringing the above to my attention.

Christopher C. Burt
Weather Historian

Extreme Weather Cold Heat Mini Blog

Updated: 8:31 PM GMT on August 26, 2014


Heavy Rainfall Trends

By: weatherhistorian, 7:46 PM GMT on August 22, 2014

Heavy Rainfall Trends

Yet another phenomenally intense rainfall event has occurred in the U.S. this morning (August 22nd) when 3.95” of rain in one hour was measured by a COOP observer at a site 3 miles southwest of Chicago’s Midway Airport. The return period for such at Midway Airport (according to NOAA’s ‘Precipitation Frequency Data Server’) is once in 500 years. This is similar to the Baltimore, Detroit, and Islip, New York events last week (although the Islip event was probably more in the range of once in a 1000 years). Brian Brettschneider of Borealis Scientific LLC has kindly offered this guest blog today featuring research he has done on heavy rainfall trends for 207 sites across the U.S. for a homogenous POR of 1949-2013.


Significant research has been conducted in recent years regarding changes in precipitation amounts and patterns in a warming climate. From a theoretical perspective, warmer air holds more moisture so increases in temperature should lead to increases in precipitation. On the flip side, increased temperatures may dry out soils and lakes (sources of moisture), cause air currents to change, or lead to other situations that counter-balance the increase in atmospheric moisture.

A chapter from the recently released National Climate Assessment discusses the trends in long-term heavy precipitation events for the entire U.S. during the last century. In particular, they note how the proportion of annual precipitation from extreme events has increased since the 1950's. The map below shows Figure 2.18 from that report. The map shows that large increases in very heavy precipitation events have been observed in the eastern half of the country.

Figure 1. Map from National Climate Assessment (Figure 2.18) showing the observed change in heavy precipitation events.

I am interested in knowing how the rate of heavy precipitation events has changed at smaller geographical scales. Therefore, I decided to look at all airport stations in the U.S. that have a continuous record dating back multiple decades. In this instance, a beginning point of 1949 was chosen because 207 stations have complete precipitation records between 1949 and 2013 (additional stations with 1 or 2 missing months during the same time period will be added at a future date). Here is a list of the stations used in the survey. This is also a long enough period of time to smooth out increases or decreases due to cyclical climate oscillations with short (<10 year) periods. Cooperative stations were excluded since the time of observation is not consistent from one station to the next and in some cases it changes intra-annually at single stations. Therefore, only airport stations with midnight-to-midnight reporting times were used.

The 207 stations are nicely distributed geographically with a slightly higher density east of the Rocky Mountains and a lower density west of the Rocky Mountain Front Range. The following map (Figure 2) shows the distribution of stations.

Figure 2. Locations of airport stations with complete precipitation data from 1949-2013. A total of 207 stations met the criteria.

For the purpose of this analysis, we are not studying the temporal spread of singular heavy rain events – just the frequency of high precipitation events. In fact, the year with the highest precipitation event for the 1949-2013 time period at each station is not statistically significant when grouping the years into eight categories. Figure 3 shows the year range of the highest calendar-day precipitation event for each of the 207 stations. There is a slight tendency for the records to be more frequent in recent years but the significance level (p-value) is only 0.15 and is therefore not significant at the 95% or 90% level. If there was an 85% significance category it would fall within that bound (See Figure 4). EDITOR’S NOTE: That being said, record calendar-day precipitation events are not as relevant as 24-hour precipitation events might be given that intense rainfalls do not follow neat calendar day schedules.

Figure 3. Year when highest calendar day precipitation event for all stations during the 1949-2013 time period was recorded.

Figure 4. Number of maximum precipitation events grouped by year of occurrence for all 207 stations during the 1949-2013 time period.


For each station, a linear regression line was fitted to the number of days per year that met or exceeded A) 0.05", B) 0.50", C) 1.00", and D) 2.00". The first value (0.05") was chosen as a proxy measure for the overall number of rainfall events per year. A smaller value was not used so that future research can extend the analysis to Cooperative stations. Those stations, especially early in their climate records, missed some small precipitation events. The 0.05" value allows us to determine if all precipitation events are increasing or decreasing – not just heavy events.

Once a linear regression was completed for each station at each of the four precipitation thresholds, a probability value (p-value) was computed. The p-value is a statistical measure of significance. A p-value less than 0.05 indicates that there is a less than 5% chance that the statistical trend is random. A p-value less than 0.10 indicates that there is a less than 10% chance that the statistical trend is random. By convention, a p-value greater than 0.10 is considered not statistically significant.

As an example, the Dallas Fort Worth International Airport (GHCN ID: USW00003927) saw a slight decrease in number of days with at least 0.05" of precipitation between 1949 and 2013. However, the p-value was 0.93 – indicating near total randomness in the distribution. Looking at the number of days with at least 0.50", there was an increase over time and the p-value was 0.045. Since this number is less than 0.05, the upward trend is considered significant at the 95% level. The p-value for the trend in days with at least 1.00" was 0.16 and for days with at least 2.00" was 0.70 – both not significant at the 95% or 90% levels. Collectively, we conclude that the Dallas Fort Worth International Airport has observed a statistically significant increase in the number of days with at least 0.50" of precipitation but all other thresholds were not significant.

Statistical Significance Maps

Instead of plotting percent change (or raw value change) for each station from 1949-2013, I decided to plot statistical significance – using the aforementioned p-value. For example, if a station showed at 20% increase in the number of days with 1.00" or more between 1949 and 2013, 1 or 2 years might be responsible for all of the increase. Therefore, the increase, in that example, is an aberration and not an actual trend. However, we can compute a statistical significance for that station's trend line and report back whether or not the 20% increase was meaningful at the 95% or 90% significance level. For all of the statistical significance calculations and maps, a station must have an average at least 0.5 days per year to calculate a trend – otherwise they are identified as "too few events."

Days per year with at least 0.05"

Most of the stations in the U.S. experienced no statistically significant increase or decrease in the number of days with at least 0.05" of precipitation. A band of stations from the Dakotas to the eastern Great Lakes saw statistically significant increases and some areas in the Southeast saw statistically significant decreases but most of the U.S. was nondescript.

Figure 5. Significance map of trend in number of days with 0.05" of precipitation or greater during the 1949-2013 time period.

Days per year with at least 0.50"

Using a threshold of 0.50", patterns begin to emerge. Many stations from northern Texas to the Dakotas and then eastward to include the entirely of New England saw a statistically significant increase in the number of days with at least 0.50" of precipitation. Much of the West consistently recorded a decrease in the number of days with 0.50" of precipitation but only a few stations were statistically significant.

Figure 6. Significance map of trend in number of days with 0.50" of precipitation or greater during the 1949-2013 time period.

Days per year with at least 1.00"

The statistical significance pattern is even more apparent when looking at days with at least 1.00" of precipitation. Nearly 90% of stations east of the Rocky Mountains saw an increase in the number of 1.00" precipitation days and approximately half of those stations met the 95% statistical significance threshold. Notice that some stations in the Intermountain West receive too few days per year (<0.5) to be included in the analysis.

Figure 7. Significance map of trend in number of days with 1.00" of precipitation or greater during the 1949-2013 time period.

Days per year with at least 2.00"

At the 2.00" threshold, the trend direction (positive or negative) and the significance levels are not nearly as distinct as they were for the 0.50" and 1.00" events. Nevertheless, a clear pattern exists in the northeastern portion of the country and a strong majority of stations east of the Rocky Mountains saw an increase in the number of days with at least 2.00" of precipitation. West of the Rocky Mountain Front Range, a majority of stations (65) receive too few days per year to make meaningful assessments.

Figure 8. Significance map of trend in number of days with 2.00" of precipitation or greater during the 1949-2013 time period.

All Stations Averaged Together

The primary purpose of this analysis was to assess changes in the frequency of heavy precipitation events in small geographical units. That being said, it is helpful to look at the results when all stations are averaged together. To do this, every station had an average value computed representing the average number of days with at least a certain amount of precipitation (e.g., >=0.05"). Then the value for each year was compared against that average and a percentage above or below the average value was recorded. If, for example, a station averaged 80 days per year with at least 0.05" of precipitation, a year with 88 days would be recorded as 110% of the average. This averaging technique was performed for all station, in all years, for each precipitation threshold. Using percentages prevents stations with large numbers of precipitation days (e.g., New Orleans) from overwhelming stations with small numbers of days (e.g., Las Vegas). Figure 8 shows the number of days per year with at least 1.00" of precipitation between 1949 and 2013 as an example of the spatial variability in heavy rainfall events.

Figure 9. Average number of days with 1.00" of precipitation or greater during the 1949-2013 time period.

As you can see, stations in the southeastern corner of the U.S. have far more days per year with at least 1.00" of precipitation. If, for example, the number of days in Mobile, Alabama, and Salt Lake City, Utah, both increased by 2 days per year, using raw numbers masks the change in Salt Lake City whereas using percentages does not. Therefore, any methodology that does not normalize the data runs the risk of being a de facto analysis of only those stations that have large average annual precipitation amounts.

Days per year with at least 0.05"

The change in the number of days per year with at least 0.05" is pretty chaotic across the entire U.S. There are long periods with consistently upward or downward trends but overall the values are pretty flat. Beginning in 1998, the rate of change dropped noticeably. This also corresponds to period of record or near record worldwide temperatures. The p-value of 0.54 indicates that the overall trend is not statistically significant.

Figure 10. Annual average of each station's percentage from the long-term average number of days with at least 0.05" of precipitation.

Days per year with at least 0.50"

The nationwide change in the number of days per year with at least 0.50" consistently increased for most of the 65-year analysis period. As with the 0.05" chart, the rate of change dropped in 1998. The p-value of 0.01 indicates that the trend is statistically significant at the 95% (and even at the 99%) level over the course of the analysis period.

Figure 11. Annual average of each station's percentage from the long-term average number of days with at least 0.50" of precipitation.

Days per year with at least 1.00"

The change in the number of days per year with at least 1.00" was strongly positive. The increase in the number of days per year is greater than 10% and the post-1998 deviations from the prior two charts are just 1 or 2 year anomalies on the 1.00" chart. In fact, the p-value of 0.003 indicates that the trend is statistically significant at the 99% level. A total of 17 stations that do not average at least 0.5 days per year with 1.00" of precipitation or greater were excluded from the analysis.

Figure 12. Annual average of each station's percentage from the long-term average number of days with at least 1.00" of precipitation.

Days per year with at least 2.00"

The change in the number of days per year with at least 2.00" was even more strongly positive. The p-value of 0.001 indicates a very high degree of statistical significance. A total of 65 stations that do not average at least 0.5 days per year with 2.00" of precipitation or greater were excluded from the analysis. Since the vast majority of the excluded stations are in the western U.S., this chart essentially reflects the statistical trend of the eastern half of the U.S. only. As Figures 5 and 6 demonstrate, the trends for the eastern half of the U.S. is much more prominent than for the western half.

Figure 13. Annual average of each station's percentage from the long-term average number of days with at least 2.00" of precipitation.


We showed that the rate of small precipitation events has not changed much in the last 64 years (see Figure 5). However, when the precipitation intensity rises, so does the strength of the statistical significance. Most of the eastern half of the U.S. has experienced an increase in the number of days with at least 0.50", 1.00", and 2.00" of precipitation. The western half of the country has, on average, seen a slight decline in the rate of those precipitation thresholds when enough observations are available for analysis– but not at a statistically significant level.

At the station level, the long-term trend of days at different intensity thresholds tells a more complete story than just looking at regional data using state boundaries. While data at an individual station is not sufficient to draw very many conclusions, aggregating station data in this manner allows us to draw new conclusions about how precipitation patterns change over space and time.

This blog post can also be found at Brian’s personal blog site.

KUDOS: A big thanks to Brian Brettschneider of Borealis Scientific in Anchorage, Alaska for this guest blog.

Christopher C. Burt
Weather Historian

Extreme Weather Precipitation Records

Updated: 11:34 PM GMT on August 22, 2014


July 2014 Global Weather Extremes Summary

By: weatherhistorian, 8:58 PM GMT on August 19, 2014

July 2014 Global Weather Extremes Summary

July was the 4th warmest such since 1880 according to NOAA and the 11th warmest according to NASA data (the difference in assessments is due to several factors which I’ll discuss in a future blog). It was unusually cool in the central portion of the U.S. while record warmth was observed in parts of the U.S. Northwest, Scandinavia and the Baltic nations. Several powerful typhoons made landfall in East Asia and Hurricane Arthur took a swipe at North Carolina.

Below are some of the month’s highlights.


It was the coldest July on record (average monthly temperature) for portions of the central U.S. including the states of Indiana and Arkansas. Indianapolis averaged 70.1°F (21.2°C), besting July 1947 (which averaged 70.6°F/21.4°C) for coldest such on record. In contrast it was one of the warmest July’s on record in the Pacific Northwest. Medford, Oregon experienced its single hottest month (any month) with an average temperature of 79.9°F (26.6°C) beating out July 2003’s average of 78.9°F (26.1°C). Spokane, Washington came close to its all-time warmest month with a 75.7°F (24.3°C) average, just shy of the 75.9°F (24.4°C) record set in July 1906. Because of the extreme difference in average monthly temperatures between the East and the West, the overall national average was close to normal (73.3°F/22.9°C which was just 0.3°F below the long-term normal). Precipitation was generally below average nationwide (ranking 26th driest July since 1895).

State-by-state temperature rankings (top map) and precipitation rankings (bottom map) for July 2014. Maps from NCDC.

The first Atlantic hurricane of the season, Arthur, made landfall as a CAT 2 storm in North Carolina over the Fourth of July weekend. It was the earliest hurricane on record to make landfall in N.C. but did little damage.

An EF-2 tornado struck Madison County, New York on July 8th killing 4. It tied as the 2nd deadliest tornado in state history (a tornado on November 16, 1989 killed nine and another one on August 28, 1973 also resulted in four fatalities).

A home in Madison County, New York where two died following a direct strike by an EF-2 tornado on July 8th. Photographer not identified, image from

It was an active month in the Southwest with monsoonal moisture pushing into southern California, Arizona, New Mexico, and Colorado causing localized flash flooding. Welcome rainfall in New Mexico resulted in Albuquerque enjoying its 4th wettest July on record (since 1895) with a 3.49” (89 mm) monthly total, this following years of drought. In contrast, dry and hot weather in the Pacific Northwest resulted in the largest wild fire in Washington State history when lightning on July 14th sparked a conflagration that consumed over 256,000 acres (more about this may be found in my previous blog.)

It was the warmest July on record for Canada’s Newfoundland Province.

The coldest temperature measured in the northern hemisphere during the month was -23.9°C (-11.0°F) at Summit GEO site in Greenland on July 19th.


It was a very hot month in northern Colombia where the temperature peaked at 41.4°C (106.5°F) in both the Cesar and Guajira Departments (the latter an all-time record for the department). These figures were just 1.2°C (2.2°F) short of Colombia’s national record high of 42.6°C (108.7°F) set at Chiriguana on February 16, 1998.

The warmest temperature observed in the southern hemisphere during this past July was 37.8°C (100.0°F) at Conceicao do Araguaia, Brazil on July 27th.


The big weather story for Europe during July was the record heat in parts of Scandinavia and other parts of the continent. It was the warmest month on record for Norway and Latvia, tied for 2nd warmest month in Denmark, 8th warmest for the U.K., and 9th warmest for Germany. Temperatures in Norway’s Nordland peaked at 34.4°C (93.9°F) on July 8th at Hjelntes, the highest temperature ever measured in this northern region of the country.

Precipitation varied wildly with floods in the Balkans, Romania, and northern Italy where Milan saw its wettest July on record with a 320 mm (12.60”) accumulation. In contrast it was the driest July on record in Moscow where only 4 mm (0.16”) was measured. The flooding in Romania resulted in at least two fatalities when the Gilort River overflowed the last week of the month. Two also died in Bulgaria as a result of flooding in the district of Gabrovo.

Flood waters rise to the banks of the Olt River in Ramnicu Valcea, Romania on July 28th. Photo tweeted by @gabberc

As just mentioned it was the 8th warmest (actually tied for such) July on record in the U.K. (and also the 8th consecutive month of above average temperatures). Precipitation was 82% of normal for the month. The warmest temperature observed in the nation was 32.3°C (90.1°F) at Gravesend, Kent on July 18th and the minimum 1.2°C (34.2°F) at Braemar, Aberdeenshire on July 6th. The greatest 24-hour precipitation measurement was 51.2 mm (2.02”) at Santon Downham, Suffolk on July 27-28.


More near record cold temperatures were measured at Buffelsfontein, South Africa this past July (as was the case in June) where a reading of -19.3°C (-2.7°F) was measured on July 6th and 7th (close to the national record set at the same location just last summer: -20.1°C/-4.2°F on August 23, 2013).

Ouargla, Algeria saw the temperature rise to 49.6°C (121.3°F) on July 26th, just 1.0°C (1.8°F) from matching its all-time record (P.S. on August 2nd it reached 50.4°C/122.7°F).


The hottest temperature measured in the world in July was 53.0°C (127.4°F) at Gotvand, Iran on July 17th. This tied Iran’s all-time national heat record last set on July 28, 2011 at Dehloran. Another notable all-time heat record was the 37.3°C (99.1°F) observed in Kuching, Malaysia (Sarawak on the island of Borneo) on July 26th. In Hong Kong it was the hottest July on record (since such began in 1884) with a 29.8°C (85.6°F) monthly mean.

Heavy rains the last week of July in western India resulted in a landslide in Malin, Maharashtra State killing at least 134 (and perhaps as many as 200) villagers.

A series of powerful typhoons developed in the Eastern Pacific and made landfall in China and Japan. Typhoon Rasmussen (or Rammasun) struck Hainan Island, China on July 18th with sustained winds of 155 mph and the lowest barometric pressure ever observed at a land site in China (899.2 mb/26.55”). The Super Typhoon killed 206 and caused $6.5 billion in damage in China and the Philippines. See Jeff Masters' blog posted August 18th for more details.

Typhoon Rammasun (named Glenda in the Philippines) slammed into the town of Imus southwest of Manila on July 16th with hurricane-force winds as can be seen in this image as the typhoon made landfall. Photo by Erik De Castro.


Overall, temperatures were close to normal and precipitation below normal in Australia during July.

Temperature (top map) and precipitation (bottom map) deciles for Australia during July. Maps courtesy of the Australian Bureau of Meteorology.

The warmest temperature observed during July was 33.3°C (91.9°F) at Jabiru Airport and Mango Farm, Northern Territory on July 10th and the coldest -11.3°C (11.7°F) at Glen Innes Airport, New South Wales on July 12th. The greatest calendar day precipitation measured was 215 mm (8.46”) at Cape Leveque, Western Australia on July 13th. Brisbane, Queensland saw a low of 2.6°C (36.7°F) on the July 12th, its coldest temperature observed since 1911. Amberley, part of the city’s metro area, dropped to -2.7°C (27.1°F). Needless to say, temperatures this low at low elevations of Queensland are very rare.


Kaikohe, Northland on the North Island recorded its wettest July on record with 586 mm (23.07”) of precipitation (311% of normal). Its greatest calendar rainfall was 159.4 mm (6.28”) on July 8th, which also the greatest daily amount anywhere in New Zealand for the month. The warmest temperature observed was 22.7°C (72.9°F) at Timaru, South Island on July 31st and the coldest -9.8°C (14.4°F) at Lake Tekap, South Island on July 16th.


The coldest temperature in the southern hemisphere and the world during July was –80.4°C (-112.7°F) recorded at Concordia on July 10th.

KUDOS Thanks to Maximiliano Herrera for global temperature extremes data and Jeremy Budd and NIWA for New Zealand data.

Christopher C. Burt
Weather Historian

Extreme Weather

Updated: 1:30 AM GMT on August 20, 2014


Incredible East Coast Rainfall Event of August 12-14

By: weatherhistorian, 8:43 PM GMT on August 15, 2014

Incredible East Coast Rainfall Event of August 12-14

What must have been one of the most anomalous non-tropical-storm-related precipitation events on record affected a wide area from North Carolina to Maine on August 12-14. The heaviest precipitation was confined to a relatively narrow band from the Baltimore, Maryland area, across southern New Jersey, and into coastal areas of New England as far north as Maine. Here are some details.

Submerged automobiles litter the Belmont Parkway on Long Island following the intense rainfall that deluged Suffolk County on the morning of August 13th. Photo from New York State Department of Transportation.

Peak storm totals by state (all occurring within 24 hours) but beginning on August 12th in the south and ending August 14th in the north included:

NORTH CAROLINA: 5.63” at Rendezvous Mountain RAWS site

VIRGINIA: 4.30” at Tysons Corner 2 NW

MARYLAND: 10.32” at Green Haven 1 WNW

DELAWARE: 4.10” at Odessa

NEW JERSEY: 8.94” at Millville Municipal Airport

PENNSYLVANIA: 4.30” at Beaverton

NEW YORK: 13.57” at Islip Airport

CONNECTICUT: 4.50” at Madison

RHODE ISLAND: 4.53” at Coventry

MASSACHUSETTS: 5.46” at Hatfield

VERMONT: 2.78” at Westminster West 0.9 E

NEW HAMPSHIRE: 5.26” at Newbury 4 SE

MAINE: 6.59” at Scarborough

Unfortunately (and surprisingly!), it appears no comprehensive map of the rainfall totals for the entire region has yet been produced.

The most extraordinary report was that from Islip, New York where 13.57” fell in the 24-hour period of 11 p.m. August 12 to 11 p.m. on August 13th. This established a new all-time New York State record for a 24-hour precipitation event (although NOAA reports 13.70” falling in Brewster during Hurricane Floyd on September 16-17, 1999—this value has been difficult to verify). Of the 13.57” total that accumulated at Islip an amazing 13.27” came down in just 12 hours with 9.71” in the two-hour period between 5 a.m.-7:00 a.m. on the morning of the 13th.

METARS at Islip, New York Airport during the heaviest period of rain on the morning of August 13th. NWS-New York.

At its greatest intensity, 1.76” of rain fell in one 15-minute period at Islip between 5:39 a.m. and 5:54 a.m. as this graphic above displays.

Given the intensity of the event it is remarkable that only one storm-related fatality (a traffic accident) was reported and flood damage seems to have been largely confined to submerged vehicles. This is in sharp contrast to the devastation that took place earlier in the week around Detroit, Michigan where at least three fatalities were reported and preliminary damage estimates are said to be close to $1.2 billion with over 18,000 homes flooded. Detroit Metro Airport picked up 4.57” on August 11th, its 2nd greatest calendar day precipitation event on record (following 4.74” on July 31, 1925). Dearborn, Michigan had the top rainfall report in the area with 6.31”.

Aside from the rain on Long Island, the Baltimore, Maryland region also saw record-breaking rainfall with the 6.30” on August 13th being their 2nd greatest calendar day total (following 7.62” on August 23, 1933 during a tropical storm). However, Hurricane Connie dumped 7.95” in 24 hours on the city on August 12-13, 1955. Again, it was the rainfall rates that were most extraordinary during the recent event. 3.91” fell at the Baltimore-Washington Airport between 12:29 p.m. and 1:32 p.m. on August 13th, basically a one-hour period. The NWS said this rate of rainfall had an occurrence period of once in 500 to 1000 years.

Further north, Portland, Maine picked up 6.43” on August 13th, its 5th greatest calendar day rainfall and greatest such during a non-tropical-storm-related event (the city’s greatest daily rainfall occurred during Tropical Storm Lili on October 22, 1996 when 11.74” was measured, part of a 24-hour record of 13.32” on October 21-22). Of interest, similar to Islip and Baltimore, was the intensity of the rainfall with 2.57” falling during the one-hour period between 9 p.m.-10 p.m. on August 13th, a new record (tropical storm-related or not). The previous hourly record was 2.08” during Tropical Storm Bob on August 19, 1991. In just two hours (9 p.m. to 11 p.m. Wednesday night) 4.21” fell, another all-time record, this time for a two-hour period. The figure was said to be a once in a 200-year extreme precipitation event.

The cause of the excessive precipitation was unusually moist air from the south over running an occluded front that was draped over the eastern U.S. A small low-pressure system developed on the front and dragged the attendant precipitation northeastward to Maine. The core of the heaviest precipitation followed a narrow slot up the eastern seaboard with the heaviest rain cells training over one another. This is why Central Park in Manhattan, just 40 miles west of Islip, picked up only .78” and sites 40 miles east of Islip only .50”.

The 7 a.m. ET Daily Weather Maps for August 12th (top) and August 13th (bottom). NOAA Daily Weather Maps.

As always happens when something exceptional weather-wise, such as this week’s extreme precipitation events, occur the question of how this might relate to global climate change pops up. I am not qualified to answer that question but here is a recent blog posted on WU by Dr. Marshall Shepherd of the University of Georgia’s Atmospheric Sciences Program that addresses this question.

Christopher C. Burt
Weather Historian

Extreme Weather Precipitation Records

Updated: 9:50 PM GMT on August 15, 2014


U.S. Wildfire Season as of August 12th

By: weatherhistorian, 7:35 PM GMT on August 12, 2014

U.S. Wildfire Season as of August 12th

It has been one of the hottest summers on record for the Pacific Northwest and especially for central and western Washington State where the largest wildfire on record (for the state) has finally been almost 100% contained. However, in spite of the devastation in Washington, the U.S. fire season has (so far) burned ‘only’ 2,533,648 acres, which is just 51% of the 10-year running average for this time of the year.

The temperature reached a daily record 96° in Seattle, Washington yesterday (August 11th) as the blazing hot summer of 2014 in Washington continued. July was Spokane’s 2nd hottest month on record (any month) with an average monthly temperature of 75.7°, just shy of the all-time record of 75.9° set back in July 1906. Ironically, firefighters announced yesterday that they have now almost fully contained the Carlton Complex fire which was ignited by lightning on July 14th and burned 256,108 acres and 312 homes (with one fatality) in an area of central Washington about 200 miles east of Seattle. It was the largest wildfire in the state’s history.

The Carlton Fire Complex bears down on Brewster, Washington on July 18th. Twitter image, photographer not identified.

Pyrocumulus form above the Carlton Complex fire as seen in this aerial image during the early stages of the fire’s development in mid-July. Photo from AP.

All-told, wildfires have now burned 323,721 acres in Washington so far this summer with many still active as the map below illustrates.

Map of locations of active major wildfires burning as of August 12th. As can be seen, virtually all of them are occurring in the Pacific Northwest. The color coding is related to the priority and type of incidence teams each fire is being given by the respective agencies involved with each threat. Map from the National Interagency Fire Center based in Boise, Idaho.

As of August 12th here is a list of acres burned in each state:

OREGON: 140,249
IDAHO: 85,241
MONTANA: 1,655

What is surprising is that California has not yet had a truly catastrophic wildfire (so far) given the record dry conditions and extensive lightning activity. Just yesterday (August 11th) some 11,678 lightning strikes were recorded as monsoonal moisture edged into the eastern portion of the state.

Lightning strikes over California on August 11th. Although the source of the storms that produced all this activity were of seasonal monsoon origins, very little precipitation reached the ground making for extremely dangerous fire conditions. Map from BLM and NWS-Sacramento.

The largest active fire in California at the moment is the so-called Bald Fire Complex (#19 on the map) in the Lassen National Forest where 39,736 acres have so far burned. Of course, the worst of California’s fire season has yet to get under way since September through November is traditionally the most dangerous time of the year fire-wise. Despite, the sobering statistics, the year 2014 has, as of August 12th, seen the 2nd lowest amount of acreage burned nation-wide over the past 10 years. Since 2004, only 2010 saw fewer acres burned.

Table of annual number of fires and acres burned as of August 12th over the past 10 years. This year is running just 51% of average so far as acreage burned and 71% of average total number of fires. Given the drought situation in California it is unlikely that this pattern will continue into the fall. Table from National Interagency Fire Center. Statistics for acreage burned every full year going back to 1960 can found here on the NIFR web site.

The fire situation is much worse in Canada where some 8.5 million acres have burned this summer in the country’s Northwest Territories. Angela Frtiz reports this from the Capital Weather Gang at the Washington Post. Sweden is also suffering an extreme wild fire event as this report details.

Christopher C. Burt
Weather Historian

Extreme Weather Fire

Updated: 1:34 AM GMT on August 13, 2014


Tropical Storm Iselle and Big Island Rainfall Reports

By: weatherhistorian, 7:58 PM GMT on August 08, 2014

Tropical Storm Iselle and Big Island Rainfall Reports

Tropical Storm Iselle made landfall along the southeastern coast of Hawaii’s Big Island early Friday morning bringing some fairly strong winds and big waves. However, it was the potential of torrential rainfall and possible flash flooding that was of greatest concern. So far, this has not materialized in any significant way, at least for Hawai'i's Big Island.

Although the final reports are not yet available it would appear that the rainfall may not have been as dramatic as expected given the topography of the island and the slug of moisture that Iselle tossed upon it. So far (as of 8 a.m. HST on Friday August 8th), the top amount reported has been 14.51” at Kulani (elevation 5,050’). Below is map of some other rainfall reports from across the island (not final totals):

A sketchy map of some rainfall reports on the Big Island as of early Friday morning. Note the lack of precipitation along the western shores where the rain shadow of Mauna Kea and Mauna Loa holds sway. This map, of course, will be updated later today or Saturday. Map from The Weather Channel (as of about 4 a.m. HST).

Rainfall reports for the Big Island as of 8 a.m. HST. By this time the rainfall had, for the most part, ended along the eastern shores including Hilo where a total of 3.34” was reported: not really a substantial amount for this normally very wet location and where 27.24” once fell in 24 hours (on November 1-2, 2000). Table from NWS-Honolulu. You can follow this link for updated rainfall reports for all locations in the state of Hawaii.

The heaviest rains have occurred on the windward slopes of the volcanoes and, at sea level locations, along the southeastern coastline. This is, climatologically, the norm year around as the map below illustrates.

A rough map of the Big Island’s annual average precipitation. There are few gauges in the region of heaviest rainfall along the steep slopes of the mountains just west of Hilo. Map from Hawai’

According to the rainfall atlas produced by the Geography Department of the University of Hawaii-Manoa the wettest location on the Big Island is a site known as Makakanaloa 2 located at 2,675’ elevation (19.810°N, 155.191° W) 13 miles northwest of Hilo and where an average of 7613 mm (299.72”) of rainfall accumulates each year. The gauge here was operated under the supervision of the State Division of Forestry from 1934-1953. The driest location, according to the rain atlas, is the Mauna Kea Observatory (13,631’) with an annual average precipitation (which includes snowfall) of just 207 mm (8.15”). Amazingly, the summit site is only about 18 miles west of the wettest site mentioned above.

Christopher C. Burt
Weather Historian

Extreme Weather Precipitation Records Tropical Storms Mini Blog

Updated: 8:00 PM GMT on August 08, 2014


First 100°F Temperature on Record in the Baltics

By: weatherhistorian, 7:24 PM GMT on August 05, 2014

First 100°F Temperature on Record in the Baltics

The 37.8°C (100.0°F) temperature observed at Ventspils, Latvia on August 4th was the first time on record that a reading of 100°F has been measured in any of the Baltic nations (Latvia, Estonia, and Lithuania). The heat wave has also affected Poland, Belarus, and Sweden where a massive forest fire, said to be the worst in the nation's modern history, rages out of control.

It has been a warm past month in Ventspils, Latvia with 10 out of the past 30 days reaching 30°C (86°F) or more. The normal daily maximum temperature for July and early August is just 19°C (66°F). The 36.6°C (97.9°F) on August 3rd was a new Latvian national record only to be shattered the following day with the 37.8°C (100.0°F) reading. Climate table from OGIMET.

The record was especially unusual since Ventspils (also known as Ventspili) is a coastal location situated right along the shores of the Baltic Sea. The previous Latvian record of 36.4°C (97.5°F) on August 4, 1943 (same date!) was measured at Daugavpils which is an inland location near the border of Belarus and where hotter temperatures might be expected vis-à-vis a coastal location. The reason for the excessive temperature at Ventspils, this time around, was a strong offshore flow caused by a high-pressure system centered over northeast Russia and Finland.

A strong surface high pressure centered over Finland and northeast Russia (bottom map) along with a 210-meter positive height anomaly (top map) created a southeast (offshore) flow over the Baltic nations early this week leading to the record temperatures at the Latvian coastal location of Ventspils. Maps of 12Z ECMWF models for August 4th courtesy of Nick Wiltgen at The Weather Channel.

Aside from Latvia, record or near-record temperatures have also been observed in Belarus, Estonia, Lithuania, and Sweden. The capital city of Minsk in Belarus broke its all-time heat record on August 3rd with a 35.6°C (96.1°F) reading which surpassed its former record of 35.0°C (95.0°C). The top temperature in all of Belarus was 36.5°C (97.7°F) at Ma’rina Gorka (also on August 3rd) which was short of the national record of 38.9°C (102.0°F) set at Gomel on August 8, 2010. In Lithuania it reached 36.6°C (97.9°F) at Klaipeda on August 3rd (short of the national record of 37.5°C/99.5°F set at Zarasai on July 30, 1994) and in Estonia top honor went to Niqula with 33.5°C (92.3°F) on August 4th, well short, however, of the national record of 35.6°C (96.1°F) at Voru on August 11, 1992. The heat wave has also affected Poland where temperatures as high as 35.4°C (95.7°F) were observed at Ustka on August 3rd.

Late word from blog reader Blair Trewin (Australian Bureau of Meteorology) notes that the Swedish met service (SMHI) has reported at temperature of 35.1°C (95.2°F) at the town of Falun on August 4th and that this is the hottest August temperature observed in Sweden since 1992. Sweden’s national record is 38.0°C (100.4°F) set at Ultuna on July 9, 1933 and also at Malilla on June 29, 1947. A massive 15,000-hectare (37,000 acre) forest fire in central Sweden, described in the press as “the largest in modern [Swedish] history” is threatening the town of Norberg (population 4,500). One death has so far been attributed to the conflagration.

This large forest fire in central Sweden is threatening the evacuation of the entire population of the town of Norberg (population 4,500). Photo credited to TT, ‘The Local: Sweden’s news in English’.

KUDOS: Thanks to Maximiliano Herrera, Blair Trewin, and Nick Wiltgen for their contributions to the data and blog reader barbamz for news about the Swedish fire.

Christopher C Burt
Weather Historian

Extreme Weather Heat Fire


National 24-hour Precipitation Records

By: weatherhistorian, 8:10 PM GMT on August 01, 2014

National 24-hour Precipitation Records

Earlier this week, on July 28th, both Holland and Germany saw some incredible rainfalls that approached their respective all-time national records for greatest 24-hour precipitation totals. Here are some details on these events as well as a ‘potted’ list of some other national records of such.

Munster, Germany Deluge of July 28th

On the afternoon of July 28th heavy thunderstorms developed over portions of western Germany and remained stationary for several hours depositing prodigious amounts of rainfall in and around the city of Munster (among other sites). A rain gauge at Munster’s main sewage works measured 292.5 mm (11.52”) of rainfall in a 7-hour period between 17:00-00:00 UTC. Of this, an amazing 163.5 mm (6.44”) fell in a single hour ending at 20:00 UTC and 261.5 mm (10.30”) in just 3 hours (see table below).

Hourly precipitation totals at the Munster Sewage Works Station on July 28th. The daily total of 292.5 mm (11.52”) was likely the 2nd greatest such on record for Germany. Thanks to Michael Theusner for link to this data.

According to Michael Theusner of Klimahaus in Bremerhaven, Germany, the 292.5 mm figure was likely the 2nd greatest 24-hour precipitation to be officially observed in modern German climate records (following the national record of 353 mm/13.90” at Zinnwald-Georgenfeld on August 12-13, 2002 during the great Elbe Flood that summer). The one-hour total of 163.5 mm might also have been the 2nd greatest for such a period of time, being short of the 200 mm (7.87”) that deluged the town of Miltzow in one hour on September 15, 1968. The three-hour total is almost certainly a new German record for that time period, although records for three-hour rainfalls are not on the books.

Table of official German national precipitation records for various periods of time. Those highlighted were related to the disastrous Elbe River floods in August of 2002. Table from monograph about Elbe River floods written by Bruno Rudolf and Jorg Rapp for the DWD-Offenbach, 2003.

Netherland’s Rainfall on July 28th

Another cluster of thunderstorms, similar to those that brought the deluge to Munster on July 28th, also affected portions of Holland where 24-hour precipitation totals topped out at 160 mm (6.30”) in Maarssen/Utrecht and 132 mm (5.20”) at Deelen. Radar estimated totals in the Maarssen/Utrecht area indicated rainfall accumulations as high as 210 mm (8.27”). Being estimated, these are not considered as official and thus fall short of the ‘official Dutch national 24-hour precipitation record’ of 208 mm (8.19”) set at Voorthuizen on August 2-3, 1948. At Deelen, 76 mm (2.99”) of the rainfall occurred in a single-hour period, which is just short of the national record for such of 79 mm (3.11”) set in an hour at Herwijnen on June 28, 2011.

Measured rainfall totals for the 48-hour period of July 27-29 in the Netherlands. Virtually all of these amounts fell on July 28th. Map from Koninklijk Netherlands Meteorological Institute.

Some Other Possible National 24-hour Precipitation Records

Below is a chart of some other possible national 24-hour precipitation records from a selection of various countries around the world. This is a ‘potted’ list at best, and although some of the figures (especially some of those for Europe, North America, Australia, New Zealand, and certain countries in Asia and South America) are considered ‘official’ by the nation’s respective meteorological agencies most of the figures are simply what I have been able to discover researching published works such as Elsevier’s 15-volume ‘World Survey of Climatology’ series and the U.K. Met Office’s ‘Tables for Temperature, Relative Humidity and Precipitation for the World’ (a six-volume series) as well as many other scientific books and journals related to national climatologies. However, that being said, many of the above mentioned works date to the 1960s and 1970s and so do not reflect more recent data.

Unfortunately, I am only rendering the precipitation amounts in inches rather than including metric figures since, in many cases, the figures have been translated back and forth already between the two measuring systems and inaccuracies increase with each new translation. At some future date, when I have more time, I will go back and source each of the figures and determine whether the original data was provided in English units or metric units.

I simply include this list as something of interest, not to be considered an actual reliable list of official records. Hopefully, some readers will be able to correct, update, or add some more data to the list.

A FEW NOTES: The Chinese figure is of very dubious accuracy. The Indian figure is derived from a two-day measurement of 98.15” and so it is likely that the wettest single 24-hour period during this event was greater than half the total. Much higher figures for Japan and Taiwan have appeared in scientific literature but are not included since those figures have not been officially recognized by their respective meteorological agencies. The U.S. record is derived from a bucket-survey and appears to have recently been modified from 43” to 42”. Although the NCDC has rejected other ‘bucket survey’ figures in the past, for some reason they seem to be willing to consider the Alvin figure reliable and “official”.

KUDOS: Thanks to Michael Theusner of Klimahaus, Bremerhaven for German data and blog reader RRKampen for Netherlands information.

Christopher C. Burt
Weather Historian

Extreme Weather Precipitation Records


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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About weatherhistorian

Christopher C. Burt is the author of 'Extreme Weather; A Guide and Record Book'. He studied meteorology at the Univ. of Wisconsin-Madison.