Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 755 PM EDT Tue May 03 2022 Valid 12Z Sat May 07 2022 - 12Z Wed May 11 2022 ...Overview... Over the weekend, a mean trough in both the surface and upper levels is forecast to drift into the western mainland and inland during the early part of next week along with some moisture, supporting some showers over those areas. An initial upper low over the Gulf of Alaska Saturday should weaken and get shunted into western Canada as next week begins, but a mid-latitude upper low in the Pacific slowly drifting northeastward for the first half of next week should be the more impactful feature. There is uncertainty in how this feature will interact and possibly phase with the troughing farther north, which affects its timing and track of an associated surface low, and therefore precipitation for the southern coast of Alaska as well. In general a wetter pattern is expected there next week, but with uncertainty in rain amounts and timing. ...Guidance/Predictability Assessment... Model agreement as the medium range period begins Saturday is fairly good with the larger scale features: the upper low over the Gulf of Alaska, another centered well south of the Aleutians in the Pacific (around 40N and the International Date Line), and troughing just west of Alaska stemming from an Arctic upper low, with perhaps weak ridging eroding in the southwestern Interior. Troughing coming into western Alaska on Sunday still shows some detail differences among models, like the GFS runs showing one deeper 500mb trough 12Z Sunday while the ECMWF/CMC show two shortwaves. With these differences, utilized a blend of the 12Z deterministic guidance to get to a middle ground solution. However, the evolution of this northern energy through the first half of the workweek is uncertain along with the upper low farther south. There has been considerable model waffling with how phased the northern and southern features will get. The GFS runs remain more connected with the features with ECMWF ones more separate. However, the 12Z and 18Z GFS show slightly more separation than older runs and show a slower upper low, while the 12Z ECMWF has sped up a bit with the upper low, leading to somewhat better model consensus in both the upper and surface low positions. The general trend was for slower upper/surface lows than the previous WPC forecast, so today's forecast leaned that direction. The WPC 500mb heights show a closed low to the south but still with some indication of a connection at times to the Arctic low/trough, for the purpose of compromising between the more separated ECMWF/EC mean and the less separated GFS/CMC/GEFS mean. The 00Z EC mean seemed particularly slow compared to the consensus of other guidance and the 12Z EC mean did come in a little faster. Overall troughing should be persistent over much of Alaska by early-mid next week, though with potentially some separation in features allowing for more zonal flow in between around the AK Peninsula, and this will continue to be refined. The troughing may get hung up west of a strong eastern Pacific ridge. The latter part of the WPC forecast used a blend of the latest available GFS, ECMWF, CMC, and GEFS and EC mean guidance, with the blend tempering individual differences. ...Weather and Hazard Highlights... Chances for mostly light precipitation across the southeastern mainland in conjunction with the initial upper low should become more scattered and then diminish into early next week, but increasing chances are likely across the western mainland shifting into interior Alaska Sunday into Monday as troughing and a surface front/trough pass across the area. Precipitation chances across southern Alaska next week are less certain as they depend on upper level flow interactions and the resultant surface low position. A more phased solution would bring deeper moisture into the Alaska Peninsula to Southcentral and the Panhandle, allowing for heavier precipitation, like GFS runs show, while EC runs keep the area drier given more separation in the upper level features. At this time, the most probable outcome still seems to be for some moisture to spread across areas from the Alaska Peninsula through the southern coast and Panhandle early to mid next week, with some locations reaching at least moderate intensity for a time. Temperatures should be fairly stable and not terribly anomalous during the period. The Panhandle to far southeastern mainland can expect cooler than normal conditions for both lows and highs. Much of the mainland should see around normal to above normal lows, with more of a mix in terms of high temperatures. Sufficiently warm temperatures combined with the remaining snow pack could present flooding concerns in the Tanana basin between the Yukon and Alaska Range of the eastern mainland. Tate Hazards: - Flooding possible across portions of eastern interior Alaska, Fri-Tue, May 6-May 10. 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