500-hPa stream function). Interestingly, comparison of the observed 2009-2010 winter to the analogs that have been constructed from the earlier period show a significant difference in temperature for our region and across much of the Northern Hemisphere.
In other words, if the atmospheric circulation that occurred during this past winter had occurred sometime during the 1960s-1990s, then it would have actually been colder by roughly 1°C-2°C (1.8°F-3.6°F).
When averaged for the Northern Hemisphere, this result was also true for the other winters between 1991 and 2010 - the observed winter conditions of the recent two decades were warmer than the analogs constructed from the 1961-1990 historical data by an average of 0.5°C (0.9°F).
So why were we "spared" from a colder winter?
By itself, the constructed analogs technique does not necessarily point to a particular reason or mechanism as to why the 2009-2010 winter was warmer than the analogs drawn from the historical data.
It's possible that our "luck" during the recent winter resulted from some combination of global warming and the long-term, decade-to-decade variability in the Atlantic Ocean. Although it can be difficult to tease apart these factors (and such work is an active area of research), this analysis provides evidence of some important differences between the winters of today and those occurring during the mid-20th century.
Joe Casola works as a consultant, helping natural resource managers use weather and climate information as part of their decision-making process. He holds a B.S. in Chemistry from Duke University. After discovering he was a klutz when mixing chemicals in the lab, Joe decided to follow his passion for looking at clouds and earned a PhD in Atmospheric Sciences from the University of Washington. He has also worked on weather and climate issues at the National Research Council.
| November 3, 2010; 12:30 PM ET
Categories: Climate Change, Winter Storms
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