Following record warmth in the 49th state, temperatures dropped to -40 degrees in some parts of interior Alaska this past weekend, and the cold is expected to hang around for much of the week. As seen in this graphic of RTMA model data from December 6, 2016, temperatures sunk to -40 or lower.
The RTMA, or Real-Time Mesoscale Analysis model, uses surface observation data to create a highly accurate gridded analysis of past weather conditions. Thus, unlike the Weather Research and Forecasting and Global Forecast System weather models, the RTMA is not predictive.
The frigid air is blamed on a large area of high pressure over the Bering Strait, which prevented warmer air from moving northward from the Gulf of Alaska. This allowed much colder air in the vicinity of the North Pole to head south.
Link to full article: http://www.nnvl.noaa.gov/MediaDetail2.php?MediaID=1971&MediaTypeID=1