A cold blast of arctic air will surge into the Great Plains midweek rapidly charging to the Gulf of Mexico and moderating into the East. A primary concern is the extremely tight pressure gradient between a 1060 MB arctic high over Montana Thursday and a 980 MB low over Michigan Friday which will cause wind gusts from 55 to 70 mph (or more) in the Upper Midwest, Midwest, Great Lakes region and into the Northeast Thursday into Friday. The immediate Atlantic Seaboard is also at risk for very high wind on Friday.

Last week, the Nino SSTA regions were warmer. Three of the four Nino SSTA regions remain within the La Nina threshold. The Nino34 SSTA is -0.9C which is moderate strength La Nina but slightly warmer than the previous week.

Forecast confidence is increasing for a significant snowstorm in the East later next week. ECM has an incredible amount of snow across the entire northeast quadrant of the U.S. while GFS focuses heavy snow on Virginia. With snow on the ground and following arctic air, the East will be super cold for Christmas Day and for a few days that follow.

The character of the -AO regime is about to change. The high-latitude high-pressure ridge shifts from Greenland to Alaska and gradually an Alaska “ridge bridge” toward Siberia develops. The result is increasing risk of a cross-polar arctic air surge from Siberia into North America in 7-10 days. The pattern described is often referred to as the “Siberian Express” and the Alaska “ridge bridge” phrase became popular after the North America “polar vortex” winter of 2013-14.