Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 549 PM EST Sun Dec 27 2020 Valid 12Z Thu Dec 31 2020 - 12Z Mon Jan 04 2021 ...Deep system in the western Bering late this week with strong winds... ...Overview and Guidance/Uncertainty Assessment... Upper pattern for Alaska will be driven by the eastward progression of a deep upper low from the northwestern Pacific into the Bering Sea and then into the Gulf of Alaska. Weak ridging over the Interior later this week will slip northwestward into northeastern Russia and beyond, allowing lower heights from the Yukon to move into the Tanana Valley and Y-K Delta next weekend into next Monday. The 12Z guidance was clustered enough so that a mostly deterministic blend sufficed to start. The GFS was again just a bit removed from the ECMWF-led cluster (though that also contained the parallel GFS), especially with an offshore system well south of the Aleutians Thursday that will lift into the Gulf by Friday. Over the Bering, models continue to advertise a very deep low in the 930s mb or so and have trended lower accordingly given the consistent trends the past few days. Progressive flow will keep any frontal system moving steadily eastward, including another Pacific system underneath the Bering low next weekend. Trended toward much more ensemble weighting by next Sun-Mon as timing becomes much more uncertain with these smaller-scale features. ...Weather/Hazards Highlights... Deep Bering system will bring at least a period of modest rain/snowfall and certainly windy conditions (40-50kts+) around the center. Parent low will take several days to wind down, maintaining scattered precipitation for the Aleutians/Bering Sat-Tue. Triple point low detaching from the occlusion could provide more focus for rain/snow across at least parts of the AKPen next weekend, though this has trended a bit farther south. The Panhandle may see several rounds of rain/snow as each system moves through. Temperatures will start near to above normal, especially over western areas of the mainland, Thu-Fri. By the weekend into next week, colder temperatures will filter in from the east. Anomalies of 5-15 degrees below normal may be common north of the Alaska Range with some pockets of near to slightly above normal temperatures near the Brooks Range. Below zero highs will be likely with lows 10-30 below in the valleys. Fracasso 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