Dr. Judah Cohen of AER:
In our model we have four predictors, October Eurasian snow cover extent, September sea ice concentration, El Niño/Southern Oscillation and a metric of high latitude blocking in the Eurasian sector. October Eurasian snow cover extent was above normal, Arctic sea ice extent is below normal, and there has been active blocking at high latitudes this fall. All three indicators favor a cold winter in the Eastern U.S. A La Niña is predicted for this winter, which favors a cold winter in the Northwestern U.S and a mild winter in parts of the Southern US. All four predictors together provide the forecast of cold in the Northern and Eastern US with warm in the Southwestern and Southcentral US.
Finally there seems to be the thinking (among many but certainly not all) including from the National Weather Service that La Niña favors a warm winter in the Eastern US. I am skeptical of this reasoning. I note that since 1990 there have been four warm La Niña winters and five cold Niña winters in the Eastern US. If you are familiar with my research you might understand why I am not considering winters before 1990 but I doubt that the statistics change much if previous winters are included. Therefore I remain skeptical that La Niña is a reason to confidently predict a mild winter in the Eastern US especially if La Niña remains weak.
Full Report is at Arctic Oscillation and Polar Vortex Analysis and Forecasts
via Science Matters
November 20, 2017 at 04:17PM