Strong Warming Ahead

As the super-cyclone associated with the remnants of Nuri reaches its peak intensity in the western Bering Sea, a chain of events is being set in motion that will lead to extreme warming over northern Alaska in the coming days.  An intense ridge of high pressure aloft will build over southeast Alaska and then expand over eastern Alaska and the Yukon Territory, and vast quantities of warm air will be imported by the deep southerly flow over Alaska.

The table of maps below shows the predicted evolution of the 500 mb height (dashed lines) and the 850 mb temperature anomaly (departure from normal, shaded) from yesterday afternoon's GFS and ECMWF model runs.  The maps are valid at 24-hour intervals from Tuesday afternoon in the top pair to Friday afternoon in the bottom pair.  It's clear that the model agreement is excellent and therefore confidence is high.  Remarkably, the models show 850 mb temperatures reaching more than 20 °C above normal over the eastern North Slope - I've created these maps before, but this time I had to adjust the color scale to accommodate the magnitude of the anomaly.











The good agreement between the models provides a nice opportunity to test my recent hypothesis that the National Weather Service temperature forecasts for Fairbanks are sometimes too conservative at the end of the short-range forecast period when the models agree in predicting a major anomaly.  The 850 mb temperature anomalies predicted for the closest gridpoint to Fairbanks are shown below, and the current NWS forecast for the high temperature each day is also shown.

Date (AKST)GFSECMWFMeanNWS High Temperature
3pm Nov 11+11.3C+13.5C+12.4C31F
3pm Nov 12+17.2C+15.3C+16.2C34F
3pm Nov 13+15.8C+17.7C+16.7C34F
3pm Nov 14+13.6C+14.3C+13.9C26F

We see that the NWS forecast is already calling for well above-normal temperatures, and in fact the forecast doesn't look conservative at all; the normal high temperature in Fairbanks on November 13 is 11 °F.  However, the record high temperatures for this time of year are in the 40s, and the upcoming event looks like it intends to set some records.  Could the thin (2-inch) snow pack be in danger in Fairbanks?  We'll find out soon.