The image above shows 500 millibar heights for January 23rd. That big purple spot in the Great Lakes shows extremely low heights across the Great Lakes. There is only one system that can create such a big synoptic area of such low 500mb heights, and that is the polar vortex. This is essentially 1985, but less amplified. Daytime HIGHS would reach in the negative double digits for cities like the Quad Cities IA, Chicago IL, just to name a few.
Now, before you get excited, know that this is the first run the GFS has shown this, essentially Patient Zero. If we want to see this scenario actually have a chance of verifying, we need to see this same forecast output be shown again for the next week to even have a CHANCE in my book. While this is all good fun and excitement, you have to balance out just what the chances of this happening are. The polar vortex will drop south, the big question is how far south. Obviously the GFS thinks its best to fly south and bring winter with it.
UPDATE at 10:00 AM CT: The overnight 0z ECMWF model agreed with the ECMWF in dropping the polar vortex south into the Great Lakes in a very surprising consensus between the two global models:
|Day 10 500mb height anomalies|
|Day 10 850mb temperature forecast|