Winter '12 / '13 - Waiting in the Wings

Latest Week2 ensemble forecast from NOAA/s Physical Science Division's Global Forecast System (GFS 1998) shows a decided change in the long wave pattern over the NHEMI.

RED (BLUE) areas are positive (negative) anomalies.

The current high zonal index to an occasional Trof-W / Ridge-E flow regime flips to Ridge-W / Trof-E with a hi-latitude block setting up over Greenland and the establishment a strong PNA ridge.

The sub-tropical jet turns its attention away from the PAC NW gets busy delivering tropical moisture across the southern tier and Gulf of Mexico.

Low-level cold air is indicated east of the Rockies courtesy the strong PNA ridge along 125°W (preferred position for EC snow storms) and the Greenland block.