Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 647 PM EST Thu Feb 17 2022 Valid 12Z Mon Feb 21 2022 - 12Z Fri Feb 25 2022 ...Overview... Guidance generally agrees that mean upper ridging will prevail from the eastern Pacific through Alaska and northwestern Canada for most of next week. A Bering Sea/Aleutians shortwave (with associated surface system) should briefly dampen the upper ridge over the mainland as it passes through around Tuesday. Meanwhile a deep and broad system will likely track over the far northwestern Pacific toward the western Bering Sea, with one or more leading surface fronts sweeping across the Bering Sea/Aleutians. There could be one or more waves anchoring/embedded within these fronts as well. By the latter half of the week a fairly strong gradient could set up over the Alaska Peninsula and western mainland, between these fronts and high pressure moving from the mainland into western Canada. The combination of the early-week system and the evolving pattern mid-late week should focus highest precipitation totals across the Alaska Peninsula and farther east along the southern coast. ...Guidance/Predictability Assessment... During the first half of the period, the primary consideration was to keep the 12Z CMC out of the starting blend for today's forecast as it was deeper and farther west (near Bristol Bay into the southwestern mainland) with a potential wave that other guidance depicts as a weak feature tracking near the southern coast. There are still timing differences for the system tracking out of the northern Bering Sea (ECMWF remains slowest) with the ensemble means supportive of their respective parent models. An intermediate solution seems reasonable given the array of guidance. For the latter half of the work week, consensus agrees on the upper ridge rebounding over the mainland. Ensemble means have been trending noticeably stronger with the ridge over the past couple days, supporting a reasonable component of operational guidance which is mostly stronger than the means aside from the CMC--which in this time frame happens to have an Arctic upper low/trough that does not compare well to most other solutions. Toward Thursday-Friday the recent operational model runs suggest increasing uncertainty over the shape and exact location of the upper ridge along with details of any shortwave energy that could either push into it from the east (an option that seems to be decreasing in potential) or from the North Pacific. There are also various ideas for individual waves that could track from the North Pacific through the eastern Aleutians/Alaska Peninsula and into the eastern Bering Sea. Above preferences led to emphasizing the 12Z ECMWF/GFS/UKMET (from more to less weight) for the first half of the week, followed by trending to 40 percent total 12Z GEFS/00Z ECMWF mean weight late in the forecast while keeping 12Z ECMWF input and splitting the GFS among its 12Z and 06Z runs. This reflected a general signal for some North Pacific into Bering Sea waviness into Thursday while becoming more conservative with specifics by Friday. ...Weather/Hazard Highlights... Expect two main episodes of significant precipitation next week. The first will be ahead of an upper shortwave/frontal system pushing eastward from the Bering Sea/Aleutians. Best focus should be from the eastern Alaska Peninsula/Kodiak Island to the Kenai Peninsula and possibly parts of the southwestern mainland on Monday, with meaningful totals extending mostly east of the Kenai Peninsula into the Panhandle by Tuesday. Then a fairly strong gradient ahead of an initial front crossing the Bering Sea/Aleutians should settle into an area from the North Pacific into the eastern Bering Sea/western mainland by mid-late week, leading to a precipitation focus over the eastern Aleutians and Alaska Peninsula as well as possibly some locations farther eastward. Any surface waves within this flow could bring added precipitation/wind enhancement to the east of their track. Uncertainty with specifics of upper ridging and surrounding energy late in the week leads to low confidence for how much moisture may eventually reach the southeastern coast and Panhandle. Above to well above normal temperatures should prevail over the majority of the state overall, with some exceptions. These include the central latitudes of the mainland where readings may drop below normal for a time around Tuesday or Wednesday after the passage of an upper shortwave/surface front as well as the southern two-thirds of the Panhandle which should be below normal for highs during most of the week. In both areas the lows are likely to have somewhat warmer anomalies. Rausch Hazards: - Heavy precipitation across portions of mainland Alaska, Mon, Feb 21. 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