Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 741 PM EDT Sun Apr 30 2023 Valid 12Z Thu May 4 2023 - 12Z Mon May 8 2023 ...Synoptic Overview... A synoptic scale upper trough is expected to be in place across western Alaska and the northern Bering for the middle of the week, and quasi-zonal flow south of the Aleutians. Another trough is forecast to build across the Gulf of Alaska going into the end of the week along with an occluded surface low. Meanwhile, upper level ridging across western Canada likely extends to far eastern Alaska with a likely closed high over the Northwest Territories, and a closed low west of the Pacific Northwest, forming a potential Rex block pattern. A second area of low pressure is likely to develop across the western Aleutians late in the forecast period with a ridge axis situated over the eastern Bering and far eastern Siberia. ...Guidance Evaluation/Predictability Assessment... The 12Z model guidance continues to struggle with the evolution and timing of shortwave energy tracking across the North Pacific, with the greatest model uncertainties residing near and south of the Aleutians. The 12Z CMC is already becoming out of phase with the developing trough over the Gulf as early as Thursday, and the model consensus strongly agrees on a more amplified solution compared to the more zonal solution from the CMC, so the CMC was not used during this forecast period. The past couple runs of the GFS have also been much stronger with a trailing surface low south of the Aleutians late Friday and into Saturday that has very limited ensemble support, albeit the 18Z run is not quite as strong as the 12Z run. Given the uncertainties, the forecast was mainly ECMWF/ECENS/GEFS and some of the UKMET and GFS through early Friday, and then only ECMWF/ECENS/GEFS for the Saturday through Monday time period with below average confidence. ...Weather/Hazard Highlights... The occluded surface low passing south of Kodiak Island is expected to produce a period of strong onshore flow on Thursday, with locally heavy precipitation across the favored terrain of the Alaska Peninsula, Kodiak Island, and the Kenai Peninsula. With that low dropping farther south and away from the state by Friday and beyond, the intensity of the rain and mountain snow diminishes in intensity and coverage with mainly light precipitation expected going into the weekend. Depending on the eventual track of the next low pressure system, parts of the eastern Aleutians and the Alaska Peninsula may see a return to more rainfall by Sunday and Monday. In terms of temperatures, daytime highs in the 45 to 55 degree range can be expected most days for locations south of the Brooks Range, and still quite chilly for the North Slope and Arctic Coast, likely remaining below freezing with highs mainly in the 20s to low 30s. Most inland locations will likely have overnight lows in the 20s and lower 30s, and 10s north of the Brooks Range. Hamrick 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