The GFS remains consistent on an artic blast that is expected to hit the Midwest Thanksgiving week. In addition to this, the Midwest's (especially in Minnesota and Wisconsin) first widespread snowfall is to take place. Chicago may see a few flakes fly come Thanksgiving. Looking further down the road into the first week of December, there is an even larger intusion of cooler air to take place. There are a few indications that supports this. First, is what is called the AO (Artic Oscillation) index. When negative, that means the cold air locked in the Artic typically plunges south into the U.S. providing cooler than normal weather for the northern plains, Midwest, and the Northeast. Opposite conditions when positve. The graphic below shows the Ao index going in a negative direction heading into the first week of December.
Second, the 11-15 day outlook has temperatures from the Plains states to the East coast below normal. The picture below shows this.
The day of this will be December 4 when temperatures will stuggle to make it into the 30s. The graphic below depicts the gfs model of the 850mb temperatures December 4.
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