Much of the past year a weak El Nino has held sway in the Pacific.
The U.S. based CFSv2 climate model just out Monday, is forecasting sea surface temperatures over the central Pacific to cool in coming months with a weak La Nina by winter.
You can see below that the typical La Nina winter weather pattern features a ridge over the west coast and an active storm track that digs into the Midwest. This usually brings a stout winter to the upper Midwest (cold and snowy). However, conditions tend to be less severe the further south you go towards the lower Midwest where drier and warmer periods often interrupt the cold.
Over the central Midwest (my area) the weather can often be quite erratic with significant bouts of winter weather interspersed with some major thaws when the ridge occasionally flattens allowing upper level winds to turn westerly. In the end it often comes out a wash with near normal temperatures and snowfall but it's a wild ride of extremes to get there.
One of the factors that can make or break a La Nina winter is the sea surface temperatures in other parts of the Pacific and Atlantic basins. The CFSv2 not only shows the cool sea surface temperatures of the La Nina but the warmth that's widespread in the rest of the Pacific and Atlantic.
In looking at analogs of winters with similar sea surface temperatures and a weak La Nina, one of the best fits for what could happen this winter is 2013-14. For those that remember, that winter in Iowa and many parts of the Midwest and Great Lakes had a mean side. In Iowa that winter was the coldest in 35 years and the 9th coldest on record. One of the calling cards of the winter was the prolonged nature of the cold with December the 17th coldest and February the 7th most frigid.
Snowfall was well above average, especially in the eastern half of the state where some totals exceeded 60 inches.
We all know (especially me) that it's only July and far too early to get on the train to a severe winter. However, this is the time of year that I start to look for the clues that will put the puzzle together. Sea surface temperatures and the state of the enso in the Pacific are two of the biggest drivers. We'll see if the trends in coming weeks match up with what the CFSv2 is projecting. If they do....well let's just say it could be a long winter. Roll weather...TS