Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 03:55 PM GMT del 12 Febbraio 2010
A rare Deep South heavy snow event is in full swing today, thanks to a powerful 1000 mb extratropical storm centered just south of Alabama. The storm clobbered Dallas with 11.2" of snow yesterday, the heaviest snow on record for the Dallas-Fort Worth Airport. Dallas' previous record was 7.4", set on January 15 - 16, 1964. The 14.4" of snow that has now fallen on Dallas this winter eclipses the previous record seasonal snowfall for the city--14.1" during the winter of 1977 - 1978. Yesterday's snowstorm dumped over a foot of snow along a narrow region just north of Dallas and Fort Worth, with the town of Haslet receiving 14.2".
Figure 1. The Deep South snow event of February, 12, 2010 in a visible satellite image taken at 9 am EST. Image credit: NASA GOES project.
As the storm races eastwards across the Gulf today, a wide area of snowfall in excess of four inches will affect Arkansas, Louisiana, Mississippi, and Alabama, with lesser amounts in South Carolina, North Carolina, and the extreme northwestern corner of the Florida Panhandle. As of 7am this morning, here are some selected snow amounts reported by National Weather Service:
TEXARKANA 1 N 4.0
SHONGALOO 5 N 6.0
DE KALB 8.0
MCCALL CREEK 5 W 4.0
SICILY ISLAND 4.0
HAWORTH 4 SW 7.5
IDABEL 8 SE 7.5
RATTAN 13 E 4.5
FORT WORTH 12.6
ROYSE CITY 12.0
POINT 3.7 ESE 11.0
EAGLE MOUNTAIN 10.5
FRISCO 1.9 N 10.3
JACKSBORO 6.2 SW 10.0
NORTH RICHLAND HILLS 10.0
OAK CLIFF 9.5
PRINCETON 3 N 9.5
FORT WORTH 14 N 9.0
As we can see from a plot of the frequency of U.S. snowstorms between 1900 - 2001 (Figure 2), heavy snow events of 6+ inches occur about once every ten years for Dallas, and between once every ten years and once every 100 years for the portions of Louisiana, Mississippi, and Alabama that may end up getting 6+ inches from this storm.
Figure 2. The annual average number of snowstorms with a 6 inch (15.2 cm) or greater accumulation, from the years 1901 - 2001. A value of 0.1 means an average of one 6+ inch snowstorm every ten years. Image credit: Changnon, S.A., D. Changnon, and T.R. Karl, 2006, Temporal and Spatial Characteristics of Snowstorms in the Contiguous United States, J. Applied Meteorology and Climatology, 45, 8, pp. 1141-1155, DOI: 10.1175/JAM2395.1.
More heavy snowstorms occur in warmer-than-average years
Another interesting result from the Changnon et al. (2006) paper (Figure 2) is the relationship between heavy snowstorms and the average winter temperature. For the contiguous U.S. between 1900 - 2001, the authors found that 61% - 80% of all heavy snowstorms of 6+ inches occurred during winters with above normal temperatures. In other words, the old adage, "it's too cold to snow", has some truth to it. The authors also found that 61% - 85% of all heavy snowstorms of 6+ inches occurred during winters that were wetter than average. The authors conclude, "a future with wetter and warmer winters, which is one outcome expected (National Assessment Synthesis Team 2001), will bring more heavy snowstorms of 6+ inches than in 1901 - 2000. The authors found that over the U.S. as a whole, there had been a slight but significant increase in heavy snowstorms of 6+ inches between 1901 - 2000. However, a separate paper by Houston and Changnon (2009), "Characteristics of the top ten snowstorms at First-Order Stations in the U.S.", found that there was no upward or downward trend in the very heaviest snowstorms for the contiguous U.S. between 1948 - 2001, as evaluated by looking at the top ten snowstorms for 121 major cities.
More snow headed for the mid-Atlantic next week
The extreme amounts of snow on the ground in the Mid-Atlantic from back-to-back blizzards over the past week will get some more company on Monday night, when a new snowstorm will hit the region. I'm thinking that the new storm will drop another 2 - 6 inches of snow on the Baltimore-D.C.-Philadelphia region. The computer forecast models have not yet come into agreement on where Monday's storm will hit, or how much moisture it will be able to tap into, so there is still high uncertainty over how much snow will fall.
A historical precedent for "Snowmageddon": the "Great Snow" of 1717
I've commented several times this week that there is no precedent in the historical record, going back to the late 1800s, to the incredible snow blitz the Mid-Atlantic has endured. Well, it turns out there is a comparable winter, at least for Philadelphia, if one goes back in time nearly 300 years. According to Chris Burt, author of the excellent book, Extreme Weather, in 1717 four storms between February 27 and March 9 dropped a total of 3 - 5 feet of snow from Philadelphia to Boston. Snow drifts as much as 25' deep occurred in the Boston area. An account of the 1717 event was one of the first journal entries of the Massachusetts Historical Society by Cotton Mather. Chris told me he wasn't aware of any comparable events affecting Washington D.C. or Baltimore, however. Chris will be joining wunderground this April as a featured blogger, and I greatly look forward to having him put our modern weather records into historical context.
I'll probably do a short post on Saturday.
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