Highlight: Top concern with incoming “polar vortex” is extreme wind Upper Midwest/Midwest and into the Northeast Corridor where widespread power outages are likely late Thursday night into early Saturday.
Fig. 1: NOAA/NWS weather watch, warning, and advisory areas.
Discussion: The “polar vortex” episode is evolving. Wind Chill Warnings are posted for the incoming arctic air today across the northwest/northern Great Plains (Fig. 1). Bismarck, ND is -8F (now) and will stay below zero until Christmas Day. Maximum wind chill during the period is -40F to -50F mid-to-late week. A Winter Storm Watch is posted for a snowstorm extending across the northern 2/3 of the Great Plains later tomorrow and Upper Midwest to Missouri Valley by Thursday morning. By Friday morning, the snow is shifting across the Northern Ohio Valley and Great Lakes region. The 48-hour snowfall forecast by GFS through 7AM EST Friday indicates 5 to 10 in. of snow in the Midwest and several in. of snow as far south as the MO/AR state line (Fig. 2). The snow is accompanied by high wind creating large drifts of snow. As the storm moves into Canada late this week, the snow shifts across the Great Lakes and into Ontario/Quebec becoming heavier (Fig. 3).
Fig. 2-3: The GFS 48-hour snowfall valid to 7AM Friday and 7AM Sunday.
The low-pressure center moves to the eastern Great Lakes by Friday morning with <980 MB pressure descending to 970MB south of James Bay Saturday morning. The unusually low pressure coupled with very high pressure to the west associated with an incoming arctic air mass will cause an immense wind storm to form. By late Thursday night/Friday morning northerly gales stretch from the Upper Midwest southward into the central Gulf States. Storm force sustained wind will be present across Wisconsin, Illinois, and Western Michigan Friday morning. The high wind is spreading rapidly across the Eastern Ohio Valley Friday morning. Gusts to hurricane force are likely especially across the Great Lakes. Widespread power outages are likely.
At the same time (Friday morning) an east-southeast gale extends across New England bringing power outages. High wind ahead of and trailing a Friday cold frontal passage in the Mid-Atlantic region brings power outages. In this region, wind gusts of 50-60 mph are possible especially downslope the Appalachian Spine. All Northeast Corridor city areas are susceptible to high wind/power outages Friday into Saturday. The strong westerlies will usher in modified arctic air and very cold wind chills.
By Thursday morning, the arctic front is in northwest Texas. By Friday morning, the arctic front has penetrated the entire western Gulf of Mexico. The frontal passage brings a northerly gale, rapidly falling temperatures and emerging extreme wind chill to Texas through Thursday and the remainder of the Gulf States late Thursday and Thursday night.
The “polar vortex” episode is brief. The U.S. pattern moderates next week and in the extended-range a nationally warmer than normal pattern emerges (Fig. 4).
Fig. 4: U.S. gas population weight HDD forecast utilizing all models, their consensus and comparing with 24 hours ago and the 10-year/30-year climatology.