Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 759 PM EDT Sun Aug 20 2023 Valid 12Z Thu Aug 24 2023 - 12Z Mon Aug 28 2023 ...Wet pattern for much of the state with Bering Sea troughing and surface low pressure systems pulling in moisture... ...Overview... The upper-level pattern over Alaska should be relatively stagnant late this week into early next week, with upper troughing getting reinforced over the Bering Sea and ridging downstream into Southeast Alaska. Mean moist southwesterly flow and likely two surface lows tracking northeastward across the Aleutians into the Bering Sea and the western Mainland will provide increased rain chances across much of the state, generally spreading west to east in a couple of rounds. Southeast Alaska should have comparatively drier and warmer conditions with the ridge overhead. ...Guidance Evaluation/Preferences... Model guidance is quite agreeable that an upper trough axis will be in place over the Bering Sea through pretty much the entire period, though with differences in the details of shortwaves within the trough and with how much energy/troughing pushes into the Interior. Around Friday there is some potential for inland energy, with the UKMET looking anomalously strong with it though. This also causes the surface low to be farther southeast in the UKMET compared to better clustered other guidance that takes the surface low from the southeast Bering Sea along the west coast of Alaska Thursday-Friday. Thus the initial forecast blend favored the 12Z ECMWF and GFS and CMC mainly. Into the weekend, additional differences start to arise with energies coming from the north and/or west that could combine with the trough or push it east. Generally the ensemble means show the trough staying put over the Bering Sea/western Alaska, with a slight push inland by next Sunday-Monday. The 12Z GFS diverged from this by taking energy quickly east across the state over the weekend, so reduced and eventually eliminated its contribution to the model blend while ramping up the proportion of the more agreeable GEFS and EC ensemble means to half day 7 and about two-thirds day 8 given the deterministic model differences. This also worked well with another surface low with a similar track as the aforementioned one, but for late week into early next week. ...Weather/Hazards Highlights... With a surface low tracking into the Bering Sea by Thursday, rain chances and amounts are likely to increase across the southwestern part of the Mainland initially, spreading north and east through late week with the track of the surface low and an associated potential atmospheric river. Then the pattern looks to generally repeat itself, with another surface low and possibly a stronger atmospheric river producing enhanced rain totals across the Aleutians/Alaska Peninsula Friday-Saturday that will spread north and east into early next week. With both systems, precipitation totals are forecast to be highest along the Southern Coast with ample moisture there--from the Alaska Peninsula to Kodiak Island and the Kenai Peninsula and into the Prince William Sound vicinity--and farther inland in areas of terrain/upslope flow of the Alaska Range, with the Brooks Range seeing some enhancement too especially with a lingering front nearby. Snow is possible in the highest elevations of the mountains. Today's forecast shows some rain sneaking as far east as Yakutat and the surrounding areas, but the rest of Southeast Alaska is likely to be drier with just a few showers. In terms of temperatures, the eastern interior and southern Panhandle will see the best potential for above normal highs, while other areas should be near to below normal. The coolest anomalies are likely to be over the Brooks Range to North Slope to the north of a front, though the coastal communities may stay closer to average. Low temperatures look to be more above normal until early next week, though with the possible exceptions of the Seward Peninsula and northwestern Mainland. 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