The United States of Snow

We live in the United States of Snow. A rare Deep South heavy snowstorm whipped across the southern tier of states yesterday, dumping six-plus inches of snow over portions of Louisiana, Mississippi, Alabama, Georgia, South Carolina, and North Carolina. Even Florida got into the act, with up to two inches recorded in the extreme northwestern Panhandle. The snowstorm left 49 of the 50 states with snow cover, according to an article by Associated Press. Hawaii was the lone hold-out. David Robinson, head of the Rutgers Global Snow Lab, said that 67.1% of the U.S. had snow cover on Friday morning, with the average depth a respectable 8 inches. Normally, the U.S. has about 40 - 50% snow coverage during the 2nd week of February. January had the 6th greatest snow cover in the 44-year record over the contiguous U.S., and December 2009 had the most snow cover of any December on record. The current pattern of record heavy snows over the the Eastern U.S. is primarily due to a natural oscillation in the Earth's climate system called the North Atlantic Oscillation (NAO). (Some prefer to discuss this in terms of the Arctic Oscillation, which is as a close cousin of the NAO, and one can use either). I discussed the NAO's influence on winter weather in a post last month. Another contributing factor is probably the current moderate El Niño event.

An all-time record snow for Dallas
The most recent storm clobbered Dallas with 12.5" of snow, the heaviest snow on record for the Dallas-Fort Worth Airport. Dallas' previous record was 7.4", set on January 15 - 16, 1964. The 15.7" 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. The snowstorm dumped over a foot of snow along a narrow region just north of Dallas and Fort Worth, with the towns of Haslet and Duncanville receiving 14.2" and 14.9", respectively.


Figure 1. Dallas' all-time record snowfall made for an un-inviting swim at this pool in nearby Flower Mound. Image credit: wunderphotographer texasdog.

A few selected snow amounts from the storm, courtesy of the National Weather Service:

...NORTH CAROLINA ...
HARKERS ISLAND 3.2 NE 8.8
HAVELOCK 2.7 S 8.5
BEAUFORT 7.0
NEWPORT 7.0
SEA LEVEL 7.0
OUTLAND 4 S 6.8
WINTERVILLE 3.5 W 6.4
CAPE CARTERET 6.2
BETTIE 6.0
BURGAW 6.0
JACKSONVILLE 6.0
MOREHEAD CITY 6.0
GREENVILLE 5.8

...ALABAMA...
BELLEVILLE 6.0
BRANTLEY 5.0
EVERGREEN 5 N 5.0
THOMASVILLE 5.0
EUFAULA 4 S 4.5
LOTTIE 4.5
MONROEVILLE 0.6 SSW 4.1
ARITON 4.0
PINSON 4.0
RAMER 4.0
TROY 4.0
WARD 4.0

...ARKANSAS...
FOREMAN 4.0
TEXARKANA 1 N 4.0

...FLORIDA...
BERRYDALE 2.0
MUNSON 2.0
JAY 1.0

...GEORGIA...
LUMPKIN 6.0
WASHINGTON 1.9 NE 5.8
LOGANVILLE 4 SSE 5.3
NICHOLSON 4.9 SE 4.8
ATHENS 3.2 NW 4.6
LA GRANGE 10.6 ESE 4.5
WATKINSVILLE 1.6 ENE 4.4
ROCKMART 9.6 SSE 4.3
TALBOTTON 4.0
HAMILTON 5 W 3.5
VILLA RICA 3.5
SENOIA 2 N 3.0
DACULA 2.5
CUTHBERT 2.0
MACON 2.0
ROME 2.0

...LOUISIANA...
SHREVEPORT 9.1 SE 6.1
NATCHITOCHES 0.9 NE 6.0
SHONGALOO 5 N 6.0
SICILY ISLAND 3.3 WNW 6.0
GOLDONNA 8.8 SSW 5.6
MONROE 5.0
PLAIN DEALING 3.3 ESE 5.0
HOMER 1.2 N 3.7
WEST MONROE 6.1 WSW 3.5

...MISSISSIPPI...
DE KALB 8.0
BUDE 6.5
VICKSBURG 6.3
BROOKHAVEN 6.0
NATCHEZ 6.0
PETAL 6.0
BRANDON 5.0
CATAHOULA 5.0
MADISON 5.0
BRANDON 1.9 NE 4.6
MERIDIAN 4.5
MCCALL CREEK 5 W 4.0

...OKLAHOMA...
HAWORTH 4 SW 7.5
IDABEL 8 SE 7.5

...SOUTH CAROLINA...
SUMMERVILLE 3.8 NE 8.2
COLUMBIA 7.3
BAMBERG 7.0
BOWMAN 7.0
EVANS 1 SE 7.0
LEXINGTON 1.6 WNW 7.0
OAK GROVE 1 SE 7.0
OATLAND 8 N 7.0
SMOAKS 7.0
HEMINGWAY 6.8
SANGAREE 6.5
ORANGEBURG 6.0
DARLINGTON 5.0
BLYTHE 4.0
CHARLESTON 3.3
BEAUFORT 3.0

...TEXAS...
DUNCANVILLE 1.7 NNW 14.9
HASLET 14.2
FORT WORTH 12.6
DALLAS 12.5
MANSFIELD 2.6 NNE 12.2
BRIDGEPORT 12.0
ROYSE CITY 12.0
SANGER 1.8 WSW 12.0
MESQUITE 3.3 ESE 11.4
NORTH RICHLAND HILLS 1.9 NE 11.3

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, Alabama, Georgia, South Carolina, and North Carolina that received 6+ inches of snow 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
I made this point in yesterday's blog post, but it's worth repeating. Another interesting result from the Changnon et al. (2006) paper of 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 than in 1901 - 2000. So, there is evidence that the average climate of the U.S. over the past 100 years is colder than optimal for heavy snow events to occur. If the climate continues to warm, we should expect an increase in heavy snow events for a few decades, until the climate grows so warm that we pass the point where winter temperatures are at the optimum for heavy snow events. However, a study by Houston and Changnon (2009) on the most severe types of snowstorms--the "top ten" heaviest snows on record for each of 121 major U.S. cities--shows no upward or downward trend in the very heaviest snowstorms for the contiguous U.S. between 1948 - 2001.

A new snowstorm for the mid-Atlantic and New York City on Monday
The extreme amounts of snow on the ground in the Mid-Atlantic thanks to back-to-back blizzards over the past week will get a fresh layer on top Monday night, when a new snowstorm will probably dump another 3 - 6 inches of snow on Washington D.C., Baltimore, and Philadelphia. The new storm is called an "Alberta Clipper", due to its fast motion and genesis location in Canada's Alberta Province. These storms are relatively dry and tend to bring lighter, fluffier snow. Once the Clipper moves out over the Atlantic off the coast of Maryland, it will pick up some Atlantic moisture and bring some heavier snows to the New York City region, potentially 6 - 10 inches.

Media coverage by the Washington Post
I did a phone-in press call with 20 media outlets on Thursday, to discuss how record snowstorms do not imply that global warming is not occurring. Participating on the call with me was Dr. Joe Romm, who blogs on climate-related issues for climateprogress.org. The audio is posted there if you want to listen.

The Washington Post highlighted a portion of the call where I said, "there's a huge amount of natural variability in the climate system", not enough years of measurements to know exactly what's going on, and "Unfortunately we don't have that data so we are forced to make decisions based on inadequate data." The article said that my statements shot down the statement by Joe Romm that "the overwhelming weight of the scientific literature" points to human-caused warming and that doubters "don't understand the science." Let me clarify that there will always be considerable uncertainty in our understanding of a chaotic system like the atmosphere. We should not demand certainty where it cannot exist, always using uncertainty as an excuse for taking no action. Keep in mind that the uncertainty goes both ways--climate change could be far worse than the IPCC is predicting, and it would be wise to buy an intelligent amount of insurance to protect ourselves. I agree with Dr. Romm's statement, and the official Statement on Climate Change from the American Meteorological Society, "Despite the uncertainties...there is adequate evidence from observations and interpretations of climate simulations to conclude that the atmosphere, ocean, and land surface are warming; that humans have significantly contributed to this change; and that further climate change will continue to have important impacts on human societies, on economies, on ecosystems, and on wildlife through the 21st century and beyond." The official statement from the UK Royal Society and UK Met Office is also one I agree with, "The 2007 IPCC Assessment, the most comprehensive and respected analysis of climate change to date, states clearly that without substantial global reductions of greenhouse gas emissions we can likely expect a world of increasing droughts, floods and species loss, of rising seas and displaced human populations. However even since the 2007 IPCC Assessment the evidence for dangerous, long-term and potentially irreversible climate change has strengthened. The scientific evidence which underpins calls for action at Copenhagen is very strong. Without coordinated international action on greenhouse gas emissions, the impacts on climate and civilization could be severe.".

Next post
Looks like the winter onslaught will slow down for a day, so I'll be back Monday with a new post.

Jeff Masters