Another amazingly snowy winter for the U.S.

As northeast Oklahoma and northwest Arkansas dig out from the two feet of snow dumped this winter's latest epic snowstorm, it's time to summarize how remarkable the snows of the past two winters have been. So far this winter, the Northeast U.S. has seen three Category 3 (major) or higher snow storms on the Northeast Snowfall Impact (NESIS) scale. This scale, which rates Northeast snowstorms by the area affected by the snowstorm, the amount of snow, and the number of people living in the path of the storm, runs from Category 1 (Notable) to Category 5 (Crippling.) This puts the winter of 2010 - 2011 in a tie for first place with the winters of 2009 - 2010 and 1960 - 1961 for most major Northeast snowstorms. All three of these winters had an extreme configuration of surface pressures over the Arctic and North Atlantic referred to as a negative North Atlantic Oscillation (NAO) and Arctic Oscillation (AO). In this situation, the band of winds that circles the North Pole weakens, allowing cold air to spill southwards into the mid-latitudes.

In the past twelve months, we've had six major Category 3 or stronger storms on the NESIS scale, by far the most major snowstorms in a 12-month period in the historical record. Going back to 1956, only one 12-month period had as many as four major snowstorms--during 1960 - 1961. New York City has seen three of its top-ten snowstorms and the two snowiest months in its 142-year history during the past 12 months--February 2010 (36.9") and January 2011 (36.0"). Philadelphia has seen four of its top-ten snowstorm in history the past two winters. The Midwest has not been left out of the action this year, either--the Groundhog's Day blizzard nailed Chicago with its 3rd biggest snowstorm on record. According to the National Climatic Data Center, December 2010 saw the 7th greatest U.S. snow extent for the month in the 45-year record, and January 2011 the 5th most. December 2009 had the greatest snow extent for the month in the 45-year record, January 2010 the 6th most, and February 2010 the 3rd most. Clearly, the snows of the past two winters in the U.S. have been truly extraordinary.


Figure 1. The six major Category 3 Northeast snowstorms of the past twelve months. Image credit: National Climatic Data Center.

A cold January in the U.S.
January 2011 was the coldest January in the contiguous U.S. since 1994, according to the National Climatic Data Center, and ranked as the 37th coldest January in the 117-year record. Despite the heavy snows in the Northeast U.S., January was the 9th driest January since 1895. This was largely due to the fact that the Desert Southwest was very dry, with New Mexico recording its driest January, and Arizona and Nevada their second driest.

A cold and record snowy winter (yet again!) in the U.S. does not prove or disprove the existence of climate change or global warming, as we must instead focus on global temperatures averaged over decades. Globally, January 2011 was the 11th warmest since 1880, but tied for the second coolest January of the past decade, according to NASA. NOAA has not yet released their stats for January. The cool-down in global temperatures since November 2010, which was the warmest November in the historical record, is largely due to the temporary cooling effect of the strong La Niña event occurring in the Eastern Pacific. This event has cooled a large portion of the surface waters in the Pacific, leading to a cooler global temperature.

Some posts of interest I've done on snow and climate change over the past year:

Hot Arctic-Cold Continents Pattern is back (December 2010)
The future of intense winter storms (March 2010)
Heavy snowfall in a warming world (February 2010)

Have a great weekend, everyone, and enjoy the coming warm-up, those of you in the eastern 2/3 of the country!

Jeff Masters