A look ahead into what the current status of the atmosphere and mid-range forecast has done to the long term outlook.
The updated January 2011 temperature anomaly forecast:
And for reference the old January forecast (issued 7 October):
The lingering blocking pattern is what caused the great change in the temperature forecast. As we move into January, the -NAO/-WPO pattern still exists, but is forecast to weaken as the indices trend towards neutral values (the NAO more so than the WPO). Should this blocking pattern break down completely and transfer into a neutral PNA, neutral WPO and weak +NAO, we will see a much more progressive pattern that will allow the above normal temperatures to work back into the eastern U.S.
My original map included a fully progressive pattern throughout the month of January, with the primary storm track going from the Pac. Northwest into Canada as the subtropical ridge lingered over the Desert Southwest. The more persistent blocking along with the strong -WPO allows the cold air to seep further into the mid-continent, which with plenty of available cold air would lead to drastic changes in the forecast like those seen above.
I would expect to start seeing the effects of the more progressive pattern around mid-January, which is somewhat-aligned with the pattern that the latest Euro weeklies show.
There is a risk for a more persistent blocking pattern or reinvigorated blocking pattern heading further into January, which would result in a cooler eastern half of the nation.
UPDATE: Analogs and weight for January: