Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 540 PM EST Thu Dec 10 2020 Valid 12Z Mon Dec 14 2020 - 12Z Fri Dec 18 2020 ...Guidance and Uncertainty Assessment... Rather unpredictable pattern evolution continues to challenge the models and ensembles with even broader details. Most stable aspect of the forecast has been the slow retreat of the upper high from near Wrangel Island northward into the Beaufort/Arctic. After several days of showing a defined upper trough or closed low moving westward/southwestward through the Interior into southwestern Alaska early next week, the models have largely dropped that idea and in place suggest modestly lower heights with the in-situ upper low near Bristol Bay becoming a bigger player as it rotates into the Gulf Tue before weakening to the northeast. However, this didn't substantially change the surface forecast, which still favors a system to lift out of the central Pacific toward the southern/southeastern Gulf (though perhaps no farther north than the latitude of Haida Gwaii) around Tue then weakening to the east. The GFS finally came around to the ECMWF/Canadian in this regard, and a blend of the 12Z guidance with the 00Z ECMWF ensemble mean proved to be a manageable starting point with only some timing changes from the forecast 24 hrs ago. For next Wed-Fri, still expect a Bering system to move east-southeastward across the Aleutians into the Gulf as the upper flow opens up and becomes more zonal. Though the GEFS members remained more progressive than the ECMWF ensembles, did not embrace this quicker solution just yet as upstream low development could slow the system. Leaned mostly on the ECMWF ensemble mean which did quicken the pace a bit from earlier runs. Details will be tough to pinpoint with this more zonal pattern, so a conservative approach served well today. ...Weather/Hazards Highlights... Strong high pressure to the north (over 1050mb) and low pressure in/near the Gulf will lead to windy conditions over the Interior early next week, though in a dry pattern. System moving toward the southern Gulf will bring some precipitation to the Panhandle, but offshore surface flow may inhibit heavier amounts as the surface low may not even reach the southern Panhandle. Next system in the Aleutians/Bering will spread light to modest precipitation to that region, perhaps more focused into the AKPen and southern coastal areas as low pressure slips eastward later next week. Details remain muddled as waves of low pressure may ride along the front, further enhancing rain and snowfall. Temperatures will be near to above normal over northern areas of the mainland early in the week but will trend colder with time as upper heights lower. Near to below normal temperatures are expected over southern areas and much of the Panhandle/eastern Interior with offshore flow at the surface. Fracasso Hazards: - High winds across portions of mainland Alaska, Sun-Tue, Dec 13-Dec 15. Additional 3-7 Day Hazard information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range Alaskan products including 500mb, surface fronts/pressures progs and sensible weather grids can also be found at: 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