Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 757 PM EDT Sat Oct 23 2021 Valid 12Z Wed Oct 27 2021 - 12Z Sun Oct 31 2021 ...Overview and Guidance/Predictability Assessment... The medium range forecast over Alaska shows a persistent pattern with an upper low northwest of the state, with rounds of troughing tracking around it. One such shortwave trough is forecast to push across the Alaska Peninsula Wed-Thu, before deeper troughing establishes itself south of the Aleutians in the northeast Pacific on Friday and tracks slowly eastward over the weekend. Model agreement starts to go awry particularly with this second trough and its associated surface low. The 12Z UKMET quickly becomes a strong/fast/northern outlier near the Aleutians Thu-Fri, while the 12Z CMC is somewhat slower/south. The 12Z GFS and ECMWF align fairly well to begin with, but by Friday into the weekend the GFS shows a northern track of the surface low closer to the Alaskan coast (and thus copious amounts of precip) compared to the farther south ECMWF. The ensemble mean solutions have somewhat of a middle ground placement of the low, so using these seemed most prudent for now. Farther upstream, a possibly closed low is forecast to move east across eastern Russia from midweek onward, while a southern stream low of possibly tropical origin tracks northeast but well to the south of the Aleutians. These features may end up combining as particularly the CMC shows, or stay separate, but confidence is low with this evolution. Therefore, WPC's forecast for Alaska began with a deterministic model blend heavily favoring the GFS and ECMWF early in the period, but gradually transitioned to using a blend of mainly the GEFS and EC ensemble mean solutions by Friday into next weekend. ...Weather/Hazard Highlights... As a relatively weak low pressure system tracks across the Bering Sea Wed and toward Southcentral Alaska Thu-Fri, precipitation and possibly gusty winds should increase somewhat from the eastern Aleutians to Southcentral, while generally rainy conditions continue for the Panhandle with convergent flow. Then by Friday into the weekend, the amount of precipitation expected will be dependent on the surface low track in the Northeast Pacific/Gulf of Alaska. Heavy amounts are possible if the low takes a northern track more like the 12Z GFS, but lighter to moderate amounts are forecast with a southern low track. Meanwhile, generally quiet conditions are expected for much of mainland Alaska, with occasional snow showers along the southwestern mainland and the North Slope and Arctic Coastal Plain. Expect above normal temperatures to dominate much of interior Alaska to start the medium range period next Wednesday. A slow cooling trend is anticipated for the entire area as heights aloft are forecast to slowly decrease due to the slow approach of the broad cyclonic circulation over the Gulf. The southwestern mainland may see temperatures well below average with this cooldown, with highs 10-20F below normal, and temperatures should become below normal farther east into the Panhandle as well. Tate 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