On Friday the National Weather Service in Fairbanks issued an "Extreme Cold Warning" for two eastern interior forecast zones: the Fortymile country and the White Mountains. This warning has rarely, if ever, been issued by the NWS in Alaska, so one might think conditions must have been extreme indeed.
But no: in a recent change of procedure, the Extreme Cold Warning simply replaces the old Wind Chill Warning for the NWS nationwide. The goal is to simplify communication of weather hazards:
"Social science research indicates users of NWS products can become confused by the number of hazard messages NWS issues before and during active weather. Especially while dangerous weather is unfolding, it is critical that NWS hazard messages are simple, short and direct."
So how cold did it get over the weekend? Well, it was certainly very chilly, with temperatures dropping below -40° in the usual cold spots of the eastern interior, and wind chills of -50°F in some places. The lowest wind chill measurement I saw was -52°F at Delta Junction early on Sunday morning. Here's a map of observed wind chill in the region surrounding Fairbanks at about that time (click to enlarge):
The following chart shows the 850mb (approx 5000 feet elevation) temperature and wind at 10pm Saturday. As is often the case, the cold air mass arrived from the northeast as it traveled clockwise around a high pressure ridge to the north. (The blank areas on the map are locations where the surface pressure is less than 850mb in the model.)
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