Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 510 PM EST Mon Nov 22 2021 Valid 12Z Fri Nov 26 2021 - 12Z Tue Nov 30 2021 ***Arctic cold over much of the Interior and rain/snow likely for southeast portions of the state*** ...Overview and Guidance Evaluation/Preferences... Through the course of the extended period, a broad and nearly stationary upper low will be located over the southern mainland of Alaska. Within this flow, there will be multiple shortwaves and surface lows that pinwheel around the southern periphery of this low and track across the North Pacific and the Gulf of Alaska. The models have been struggling for several runs on the evolution in regards to the timing and strength of each of these impulses. And because of the degree of spread among the guidance, the confidence of this forecast is below average. By Thursday, the CMC once again is more progressive/quicker with the shortwave energy rotating around the main upper level gyre over southern Alaska, the 6/12Z runs of the GFS are a little slower, which comes closer to the ECWMF solution. By Saturday, the models spread increases with shortwave and frontal timing over the northern Pacific and Gulf region. Although the increase in spread is present, a signal for a strong storm over the southern Gulf by next Monday remains. The CMC has recently been one of the better predictors of the short range periods, so only 5% was used in the initial blend to help the transition to the medium range period. The WPC forecast was primarily based from a 12Z ECMWF/06Z and 12Z GFS/12Z UKMET blend through Friday, and then increasing weights of the NAEFS, GEFS and ECWMF ensemble means through next weekend and into Monday. ...Weather/Hazard Highlights... Much below normal temperatures will persist across the southern part of the state in addition to spreading across the western part where the the greatest temperature anomalies of 15-25 degrees below normal will be present. Portions of the Interior will have widespread subzero daily maximum temperatures. With the exception for some isolated snow showers, mainly dry conditions are expected across most of the Interior and North Slope. Heavy snow and high winds are expected for the coastal mountain ranges from the Kenai Peninsula to the southeast Panhandle, and heavy rain for areas near sea level, mainly for the second half of the work week. Periods of strong winds are also likely for the central and western Aleutians with a tight pressure gradient in place owing to intense storm systems passing to the south. Campbell WPC medium range Alaskan products including 500mb, surface fronts/pressures progs and sensible weather grids can also be found at: - Heavy precipitation across portions of the Alaska Panhandle, Thu, Nov 25. - Much below normal temperatures across portions of mainland Alaska, Thu-Mon, Nov 25-Nov 29. https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html