Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 655 PM EST Fri Feb 18 2022 Valid 12Z Tue Feb 22 2022 - 12Z Sat Feb 26 2022 ...Heavy precipitation likely along the southern coast of the mainland next week... ...Overview... The majority of guidance has been fairly consistent with the forecast of the overall pattern evolution next Tuesday-Saturday. A weak shortwave (composed of multiple pieces of energy) crossing the mainland around Tuesday will temporarily dampen eastern Pacific into Alaska/western Canada mean ridging aloft. Then the ridge should strongly rebuild, amplifying as far north as the Arctic, while its axis gradually progresses eastward across the mainland. At the same time one or more potentially wavy fronts will extend southeastward from deep low pressure migrating from the northwestern Pacific into the western Bering Sea. The deep-layer flow of moisture between the mean ridge and the fronts to the west will likely favor a couple episodes of significant precipitation focused particularly from the Alaska Peninsula through the Kenai Peninsula/Prince William Sound. Lesser amounts should extend as far east as the Panhandle. ...Guidance/Predictability Assessment... The most noteworthy aspect of the 12Z guidance cycle is the fact that 12Z ECMWF trends have significantly improved operational model agreement for the large-scale forecast. To start the period on Tuesday, the ECMWF trended slower to other guidance for the overall shortwave crossing the mainland along with the associated surface reflection and precipitation shield along the southern coast. Models have been variable with the fine-scale/lower-predictability details so additional adjustments may be possible. Then later in the week the 12Z ECMWF switched to an open ridge that has been promoted by recent runs of the GFS/CMC and GEFS/ECens/CMCens means. This is in contrast to the prior couple ECMWF runs that had closed off an upper high in such a position as to hold moisture well westward of other guidance including the corresponding ECMWF means. Some GFS runs, and even momentarily the new 12Z ECMWF mean, still show potential for an upper high to close off but at a sufficiently high latitude that it would not have much influence on the forecast over the Gulf of Alaska and vicinity. Guidance is starting to shuffle around somewhat on exact strength of the upper ridge. Recent GFS/GEFS runs have trended a bit weaker from continuity though the 18Z GFS has rebounded a bit. Latest trends have contributed to an increase in confidence for the larger pattern but confidence and predictability are still quite low for exact details of one or more surface lows that are likely to develop and track over an area encompassing the North Pacific into the Bering Sea and Gulf of Alaska. Resolving the forecast for these lows will be important for refining the best precipitation and wind focus. Starting with the forecast preference of a 12Z operational model blend Tuesday into early Thursday followed by gradually increasing input of 12Z GEFS/00Z ECens thereafter (reaching 40 percent total weight by day 8 Saturday) yielded the best hint of low pressure south of the eastern Aleutians/Alaska Peninsula to near Kodiak Island in the Thursday-Saturday time frame. Finally, guidance has been variable for strength/track/timing details of low pressure tracking across the Arctic around midweek--corresponding to differences in dynamics aloft. Latest model average has trended toward better definition of a front that may drop into the North Slope and linger for a period of time. ...Weather/Hazard Highlights... The forecast is consistent in showing two primary episodes of significant precipitation next week. The first will be a continuation of an event affecting the Alaska Peninsula and southern coast (and nearby parts of the mainland) starting Monday, associated with the upper shortwave crossing the mainland on Tuesday. Best focus for precipitation by Tuesday should reach areas from the eastern Peninsula and Kodiak Island to near Prince William Sound. Somewhat lower totals will be possible along the southeastern coast and Panhandle Tuesday into early Wednesday. Then the fairly strong gradient ahead of an initial front crossing the Bering Sea/Aleutians, and possibly another front, should settle over the northeastern Pacific for a while. The resulting flow of Pacific moisture would support another episode of significant precipitation most likely to focus from the Alaska Peninsula though and a little east of the Kenai Peninsula. Some moisture should extend along the southeastern coast into the Panhandle but with lesser totals. While confidence has improved for precipitation coverage and general focus for highest totals during the latter half of the week, there is still considerable uncertainty over details of individual surface waves that will play an important role in refining the strongest emphasis for precipitation and wind. Both events next week may spread moisture over broader portions of the mainland, though confined more to western areas in the second one. Most of the state should see above to well above normal temperatures during Tuesday-Saturday. The main exceptions will be the central latitudes of the mainland where some pockets of moderately below readings may exist around midweek 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 through the period. In both areas the lows are likely to have somewhat warmer anomalies. Rausch Hazards: - Heavy precipitation across portions of mainland Alaska, Mon, Feb 21 and Thu, Feb 24. 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