Groundhog Day in a Year Without a Winter

The groundhog Punxsutawney Phil may have seen his shadow today, but the prospect of six more weeks of the mild winter of 2011/12 doesn't seem so terrible. In fact, now that we're past the typical coldest period of the year, the days are already getting longer, and the typical average temperatures are warming up day by day across the country.

In many areas, this tame winter has been unusual but not unheard of. For example, in the Northeast, the winter has been one of the warmest and least snowy on record, but it has been warmer during past winters. (The Weather Channel has a nice comparison between snow cover charts from February 2011 vs. 2012.) 

While winter temperatures have been increasing, on average, due to global warming, the mild winter this year is likely mainly due to natural climate variability, including a La Niña event in the Pacific Ocean and the orientation of the upper air jet stream.

Temperatures in the Northeast have averaged at least 5°F above average since December, with very little snow cover, according to Art DeGaetano, a Cornell University climatologist and the director of the Northeast Regional Climate Center.

“Although December 2011 and January 2012 have been warm, you do not have to go back too far to find a warmer period. The early winter of 2001-02 was the warmest at many Northeast U.S. stations. Over a longer time frame, the early winter of 1931-32 stands out as the warmest at the majority of Northeast U.S. sites,” DeGaetano said in a press release. 

The same is true in other parts of the country, although in select locations this winter may rank among the top 10 warmest on record, depending on how mild February turns out to be. In normally frigid Minneapolis-St. Paul, for example, January featured temperatures that were 8°F above average. And across the U.S., January snow cover was the 3rd lowest on average, according to NOAA (H/T Paul Douglas).

Northeast temperature departures from average from Dec. 1 through Jan. 29. Credit: NERCC.

Scientists say the mild winter will reverberate throughout ecosystems during Spring, with bigger deer populations, thanks to more accessible vegetation for them to feed on throughout the winter. David W. Wolfe, a Cornell professor of plant and soil ecology, said the lack of severe cold “will benefit some insect pests and invasive weeds like kudzu.”

“On the positive side, if you are a farmer or gardener experimenting with crops or ornamentals that sometimes can't survive a severe winter, this will be a good year for you,” he said. Last week the U.S. Department of Agriculture released new maps of plant hardiness zones, indicating a northward shift has taken place, which reflects a warmer climate. Although the Agriculture Department did not characterize the shift as being due to climate change, the movement of the hardiness zones is consistent with climate change projections for the U.S..

The mild winter may also benefit insects such as mosquitos and ticks. Jody Gangloff-Kaufmann, is a professor of entomology and a specialist with the New York State Integrated Pest Management Program, “This year, lots and lots of hungry ticks will emerge even on warm winter days. I anticipate the mosquito problems we normally see to be much more intense and begin earlier than usual if the weather continues to be mild. Even the fleas have had a boost so far this winter and many people are complaining about flea problems right now, in the middle of winter.”

Mild temperatures during the past week have set records from the Central Plains to the East Coast. New York's John F. Kennedy Airport, for example, reached 64°F on Feb. 1, breaking the old record of 62°F set in 1989.

So far this winter, Alaska has been the only U.S. state that has seen consistently severe cold weather.