Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 740 PM EDT Fri Apr 4 2025 Valid 12Z Tue 08 Apr 2025 - 12Z Sat 12 Apr 2025 ...Overview... Mean upper troughing is forecast to stretch from the Arctic southward through the western Mainland and into the northeast Pacific next week, albeit with model differences for embedded upper lows. This pattern will allow for cooler than average temperatures across western Alaska that may moderate somewhat as the week progresses. Additionally, some moisture will feed into the southern coast for precipitation chances, with modest amounts of rain and higher elevation snow that could gradually lessen later in the week. A low pressure system looks to pass south of the Aleutians late next week but could spread some rain showers there. ...Guidance/Predictability Assessment... Models continue to vary significantly regarding the position of upper lows within the main trough, even at the start of the forecast period Tuesday. GFS runs since at least yesterday have persistently shown an upper low staying just north of Alaska that is the dominant feature, with a weaker upper low farther south into the northern Pacific, and south of other guidance. Meanwhile the ECMWF indicates an upper low quickly dropping south across the western Mainland. The CMC and UKMET show an intermediate position in between the northern GFS and southern ECMWF Tuesday-Wednesday. The CMC in particular does show two embedded lows, which matches reasonably well with the EC-based AIFS and the GFS-based Graphcast. Plus its latitudinal position seemed favorable compared with the CMC/EC ensemble means. Thus the WPC forecast, like yesterday, did not favor the GFS/GEFS guidance even early in the period. Instead a blend of the CMC, ECMWF, UKMET (from most to least) plus some CMC and EC ensemble means were used. Did think that by Thursday the CMC stalled the upper low a bit too long atop the Y-K Delta while the majority of guidance had the low south by then. Thus gradually ramped up the proportion of ensemble means to half Day 6 and more Days 7-8. This also worked for the late period as the upper low drifts east through the northern Pacific (GFS runs were not favored as too far south and east) and for additional energy coming near the Aleutians (GFS runs farther north than non-NCEP guidance). ...Weather/Hazards Highlights... Upper dynamics and surface low pressure near the southern coast of the Mainland should continue coastal rain and inland/higher elevation snow over the far south and Panhandle. The precipitation is forecast to be heaviest early in the week and gradually taper off as Gulf surface low pressure weakens. One more day of heavy precipitation is indicated on the Day 3-7 Hazards chart for Monday especially considering the wet antecedent conditions by then. Some areas of lighter and more scattered precipitation (mostly snow) may extend farther north over the Mainland. Additionally, a shortwave and a surface wave moving through the Y-K Delta and vicinity could bring light snow there and into the Alaska Peninsula into Tuesday. The overall pattern should produce brisk northwesterly winds over and near the Alaska Peninsula especially through Tuesday, but with speeds likely staying below hazardous criteria. The Aleutians could see some influence from North Pacific low pressure by later week, with increasing rain chances and breezy winds. The upper trough forecast to be over the western Mainland through much of the period will support below normal temperatures (especially for highs) over the western half or so of the state especially Tuesday-Wednesday, and slowly moderating closer to normal for later week. Meanwhile above normal temperatures are likely in the East. By Friday-Saturday temperatures should be generally closer to average. 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