Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 544 PM EST Fri Nov 06 2020 Valid 12Z Tue Nov 10 2020 - 12Z Sat Nov 14 2020 ...Guidance/Predictability Assessment... Today's guidance maintains the theme of an active pattern, with strong progression especially across the North Pacific. The best model/ensemble cluster shows another deep Bering Sea system quickly replacing a leading northern Bering low Tue-Wed. Expect the second low to linger over the northern Bering for a time as it slowly weakens, and then drift a bit southeast in concert with upper dynamics. Meanwhile low pressure should develop along the southern coast of the mainland by Wed-Thu, with persistence of surface troughing and/or low pressure over the northern Gulf through Fri-Sat as the upper trough/low reach the mainland and Gulf of Alaska. Given recent guidance behavior and progressive nature of mean flow aloft, there is greater than average uncertainty for a wave that may track south of the Aleutians/Alaska Peninsula and into the Northeast Pacific Wed-Fri. The surface/500mb forecast incorporated the most common ideas from the 12Z/00Z ECMWF, 12Z UKMET/CMC, and 06Z GFS from day 4 Tue into early day 6 Thu. Then the blend quickly added 12Z GEFS/00Z ECMWF mean input, reaching 40-60 percent total by days 7-8 Fri-Sat. Overall the favored models had the best ensemble support and represented continuity fairly well for the evolution over the Bering Sea and vicinity. The 12Z GFS was somewhat west of consensus with the dominant Bering system while the 06Z GFS was at least closer even if still a bit westward. The 12Z GFS/ECMWF both trended significantly weaker/southward with the potential wave south of the Aleutians/Alaska Peninsula Wed-Thu while the CMC/UKMET were closer in principle to the 06Z GFS/00Z ECMWF. Thus far ensemble spread has been sufficient for the means to depict only a vague hint of a wave and frontal system. The preferred blend yielded a southward adjustment from yesterday while maintaining a reasonable degree of definition. This solution will provide good leeway depending on future guidance trends. Evolution of low pressure over/near the Gulf Wed onward has higher confidence Wed-Thu and Sat versus Fri, when details will depend on what becomes of the uncertain North Pacific wave. The weak/suppressed North Pacific evolution of the 12Z GFS/ECMWF would allow for persistence of Gulf low pressure through the entire Wed-Sat period in contrast to a brief southeastward emphasis on Fri. ...Weather/Threats Highlights... Deep Bering Sea low pressure will bring another episode of strong winds and areas of enhanced precipitation to locations from the Aleutians/Bering Sea into parts of the western/southern mainland. With time the precipitation emphasis will transition to the southern coast/Panhandle as low pressure becomes established over the Gulf of Alaska and northern Bering low pressure slowly weakens. The progressive North Pacific pattern will keep light precip over the Aleutians for a majority of the period. A North Pacific wave could brush the Aleutians and then extreme southern Panhandle with some precip around Wed-Fri but recent southward trends suggest lowering probability of meaningful totals. Best consensus for highest five-day precip totals extends from the eastern Kenai Peninsula through the Panhandle. Expect most of the state to see above to well above normal temperatures for about the first half of the period, with below normal readings over the Panhandle likely being the exception. The mainland should see a significant cooling trend late week into the weekend as an upper trough and possible embedded upper low move overhead. By day 8 Sat max temperatures in particular should be below normal over most areas. Rausch 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 Hazards: - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Tue-Wed, Nov 10-Nov 11. - High winds across portions of mainland Alaska and the Aleutians, Mon-Wed, Nov 9-Nov 11. - High significant wave heights for coastal portions of mainland Alaska, Mon-Tue, Nov 9-Nov 10. 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