Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 429 PM EST Sat Nov 19 2022 Valid 12Z Wed Nov 23 2022 - 12Z Sun Nov 27 2022 ...Multi-day Southeast Alaska heavy precipitation and high wind threat starting by Thanksgiving... ...Pattern Overview... An amplified upper ridge now over the state will weaken and shift eastward over northwest Canada into midweek as an amplified upper low/trough from northeast Russia works across the Bering Sea to western Alaska. New upstream upper trough amplification out from eastern Russia coupled with upper ridge amplification up through the Bering Sea/Arctic will then act to force the sharp digging of lead northern stream energies down through an unsettled North Slope/Interior later next week. This will favor a cooling trend and also sets the stage for significant phasing with ample southern stream low energies lifting over the Gulf of Alaska to produce a deep low with long fetch moisture and a heavy precipitation threat into Southeast Alaska starting around Thanksgiving and lingering over the holiday travel weekend. ...Guidance/Predictability Assessment and Preferences... Guidance remains decently clustered with the larger scale flow evolution through medium range time scales in a pattern with at least average predictability, but still struggles with the extent of stream phasing and embedded system focus to lower forecast confidence with specifics. Prefer best clustered 12 UTC GFS/ECMWF/Canadian guidance Tuesday before transition to more compatible 12 UTC GEFS/ECMWF ensemble means by Thanksgiving. This Alaska office collaborated forecast plan maintains good WPC product continuity. ...Weather/Hazards Highlights... Deep storm development up into the Gulf of Alaska now has a stronger signal in guidance for a maritime threat and to bring stormy weather with long fetch moisture to fuel a multi-day heavy precipitation threat (coastal rain/mountain snows) to focus over Southeast Alaska starting around Thanksgiving. These amounts will add to a year-long total at Juneau that may break their yearly record. Meanwhile, a cold front through western and central Alaska driven by northern stream upper troughing may also bring some precipitation in spots, but overall should be light and scattered in nature. However, strong gap winds could develop into mid-late week into southern locations in the wake of system passages. Upper troughing over the North Slope and Interior will favor unsettled conditions with some localized snows along with modest surface low/system tracks across the Bering Sea to western Alaska with overall pattern eastward translation/upper trough approach through later next week. Late period, there is also an emerging signal for another deepened low advance toward the Aleutians and southern Bering Sea over the holiday weekend with upper trough approach, with downstream upper ridging also supporting renewed digging of low/system energy over the Gulf of Alaska. Schichtel Additional 3-7 Day Hazard Information can be found on the WPC medium range hazards outlook 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