The main culprit behind the cold temperatures in December 2010 was the same one which caused the cold winter of 2009-2010; a strongly negative North Atlantic Oscillation (NAO) and Arctic Oscillation (AO). When these atmospheric oscillations are in the strong negative phase, they essentially “flip” the weather pattern across North America, with upper-level high pressure and relative warmth over Greenland and Northeastern Canada and upper-level low pressure and cold over the eastern Continental United States, including Florida (Figure 1). This pattern forces the jet stream to plunge south from northern Canada into the southeastern U.S., transporting Arctic air masses into Florida.
As mentioned above, South Florida experienced its hottest summer on record in 2010 (with the exception of Naples which recorded its second hottest recorded summer). Despite the record hot summer, average yearly temperatures at the main climate sites will end up around 1 degree below normal, which will be the coolest calendar year since the early and mid 1980s, and among the top 10 on record (except for Miami). At secondary sites Miami Beach and Moore Haven, it was the coolest year on record (please note caveat below table).