Extended range model guidance is coming into better agreement on the idea that a major arctic cold snap is headed for the Lower 48 shortly before Christmas. A powerful trough over the west Pacific will continue to prograde eastward into the central Pacific.

This trough will amplify the pattern over North America by pumping a monster ridge into Alaska.

On the eastern side of this ridge, strong northwesterly flow will tap into Siberian air and funnel it into the central United States. If this model run were to verify, December 21 high temperatures would be well below zero F across much of the Midwest.

Temperatures would be 30-40F below average! This isn’t completely out of the realm of possibility considering that the GFS and ECMWF are in fairly good agreement. There’s also more snow cover across North America this December than any other December over at least the past decade. Arctic air will be slow to modify as it moves south with that much snow pack on the ground. It’s too early to guarantee this severe of a cold snap, but the signs are there..