In the fall, most Meteorologists believed we were in store for a cold, snowy winter. The reasoning behind that is the fact that most recent La Niña winters have been cold and snowy. It was easy to make that cause and effect analysis.
So, why has it been warm and wet? We have to look more closely at the NAO. [The graphic to the left is a 'spaghetti plot' forecast of the NAO over the next few weeks. The dark line in the middle is the average...which goes negative by the middle of January.] The North Atlantic Ocean is the tilt of the jet stream east of the North American continent. When the NAO is negative, a large ridge is located over Greenland giving this pattern a nickname of “Greenland Block.” When the NAO is positive, there is low pressure over Greenland and high pressure over the eastern half of the continent.
Bottom line is if the NAO goes negative in a La Niña period we’re going to be in for quite a bit of snow! (Insert dramatic *duh, duh, dunnnnnnn* here.)
This post was written by Eric Sorensen on December 29, 2011