Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 753 PM EDT Fri Sep 03 2021 Valid 12Z Tue Sep 07 2021 - 12Z Sat Sep 11 2021 ...Pattern Overview and Model Guidance... The main large-scale upper-level feature affecting Alaska through the period will be a broad upper low spinning west of the state and dropping slowly southward from the Chukchi Sea Tue into the Bering Sea by the latter part of the week. While this feature's existence has good agreement among model/ensemble guidance, shortwave troughs and thus surface low pressure systems moving around this broad gyre are less consistent. The main shortwave of concern rounds south of the upper low, but there is uncertainty with whether it tracks south of the Aleutians into the northeastern Pacific/Gulf of Alaska or north into the Bering Sea/possibly southwestern mainland. For this forecast cycle, the bulk of the model guidance took a more southerly track with the shortwave and surface low, which was a change from yesterday's guidance and WPC's previous forecast. At the time of forecast preparation, 12Z GFS was the main player taking the features north, so leaned away from this solution in favor of a blend of the 06Z GFS and 12Z CMC/UKMET/ECMWF early in the period, and trended toward an even mix of the deterministic guidance and GEFS and EC mean solutions later in the period. Noted that the 18Z GFS came in with a southerly track of the low as well, so hopefully this is the best direction to trend, but changes in future forecast issuances remain quite possible. Additionally, there remains good model agreement for a fairly deep surface low pressure system in conjunction with a shortwave in the northeastern Pacific Tue into midweek, which is forecast to weaken Wed and especially by Thu as it approaches the Panhandle. ...Sensible Weather... A wet pattern is likely to remain across the Panhandle Tue and Wed given moist inflow ahead of the potent surface low moving toward the region, and rainfall totals could be modest to locally heavy there. Precipitation is also possible in the northwest part of the state through around Wed, with higher totals in terrain enhanced areas, some of which could fall as snow. Then, rainfall along with gusty winds are expected with the surface low currently expected to track across the northeast Pacific for the latter half of the week. The uncertainty with the low track makes it difficult to pinpoint exactly where, but generally, the Aleutians, Alaska Peninsula, Southcentral Alaska, and eventually the Panhandle could see enhanced rainfall with this feature. With general southerly moist flow across the state, cloudy conditions are likely. High temperatures are expected to be around or below normal across all but the eastern part of the mainland especially for the early part of the week. Meanwhile, low temperatures are likely to be around or slightly above average for most of Alaska through much of the period. Tate No significant hazards are expected over Alaska during this forecast period. 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