Stratospheric warming is developing on the North America side of the North Pole now, strengthening in the 6-10-day period, and peaking across northwest continent during the 11-15-day period. The attendant colder temperature trend at ground level causes a surge in U.S. gas population weight HDD for the week ending December 4th.

At day-16, the 12Z GFS shifts stratospheric warming from northwest continent indicated by all models during previous model runs, to Northern Canada. In this position, the model creates cold air quickly thrusted into the U.S. in the 11-15-day period), a dramatic cooler change.

The upper air pattern projected across Europe during the next 1-2 weeks features a deep upper-level low-pressure trough causing chilly weather for the next 10 days (at least) and excessive rainfall capable of producing flooding in parts of central, south, and southeast portions of Europe. Heavy snows are likely in the South-central Europe mountain areas, and the wet regime extends eastward to include Ukraine.

Typical of a La Nina climate, the Northwest U.S./Southwest Canada to North-central U.S. are usually the first winter targets for cold and snow. The NOAA/CPC risk of heavy snow ALERT for the last week of November indicates heavy snow risk for the Continental Divide and North-central U.S. likely to sustain following cold.