The Rossby wave machine that will be in place over the northwest Pacific for the foreseeable future will encourage persistent north Pacific blocking and a cross polar flow into Canada, as a tendency for blocking continues across the board. 1/

The result of this is a continued source of Arctic air into North America. The 12z GFS is shown as an example...note how the retrograding -NAO is key to shoving the PV towards the CONUS this weekend and next week, and the re-load towards the end of the run. 2/

The weakened stratospheric polar vortex continues to encourage tropospheric blocking. In addition, momentum deposited in the sub-tropics by a recent uptick in tropical forcing favors a weakened jet in the higher latitudes, which causes a tendency for blocking. 3/

On the GFS, note how the enhanced sub-tropical jet over the eastern Pacific and eastern Atlantic occur beneath weaker higher-latitude flow and blocking. Also, the cold air dumping into N. America and subsequent cyclogenesis near the East Coast helps the -NAO reload. 4/

With plenty of cold air available and a -NAO continuing for at least a couple of weeks, the US will lean cold thru February and it will seep into the eastern/southern US. It will remain an active pattern. The extended EPS and GEFS forecasts through Feb speak for themselves. 5/5