In a move we've been predicting for days, the NAO index should move negative, allowing some colder weather to enter the North US region. The ECMWF has latched onto this solution, as seen below in the 850 mb picture 5 days out.
The NAO should be enough in negative territory that this cold air moving into the North Plains should occur. The big obstacle, however, is the very strongly negative PNA pattern that should sustain itself over at least the next week. This will likely provide a bit of trouble for whatever colder air may come into the US. When this PNA is strongly negative, it can make for a warmer solution across portions of the east US.
|12z ECMWF NAO|