The prevailing climate pattern inspired by a Pacific La Nina is mild and we’ve certainly observed that thermal regime for most of the U.S. during late autumn. However, the polar vortex can over-rule that tropical mild influence given the proper conditions.
All models across that a stratospheric warming episode takes place across northern Canada next weekend causing arctic air to quickly form in south-central Canada followed by a southerly surge into the West and Central U.S. late next weekend and early next week. The forecast trend is STRONGER with the ferocity of this air mass and farther west. The zero degree line surges into the Interior West in 10 days and across the Great Plains to near Chicago. The opposite condition occurs in the East, delayed incoming cold therefore a warmer change.
However, the cold to warm clash generates precipitation and most of it turns to snow. The ECM ensemble forecasts snow across most of the U.S. in 15 days. The Climate Impact Company snow cover forecast certainly indicates the southern sprawl trend in the 10-day forecast.
So…the very warm autumn is about to receive a harsh pattern change in 5-6 days. The big chill will stick around for awhile. Plenty of snow on the ground for New Year’s Day!