Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 650 PM EDT Wed Sep 1 2021 Valid 12Z Sun Sep 5 2021 - 12Z Thu Sep 9 2021 ...Pattern Overview and Model Guidance... A split flow upper level pattern is expected to be in place through much of the forecast period, with a trough and intensifying surface low over the Gulf, and a broad upper level gyre near eastern Siberia with multiple shortwaves rotating around it. There will likely be some form of surface cyclogenesis over the Bering Sea by the middle of next week, although the specifics on this are highly uncertain given the degree of model spread noted in the 12Z guidance regarding timing of shortwave energy emerging from the Kamchatka Peninsula. Recent runs of the GFS have appeared to deviate significantly from the ensemble means and ECMWF/CMC over this region. The GFS is indicating a rather strong solution by next Thursday over the Aleutians, and it is quite possible the 12Z ECMWF is too fast and potentially out of phase across eastern Aleutians by the end of the forecast period. The models are in better agreement with the storm system over the Gulf region, with a generally faster trend compared to yesterday. The WPC forecast was primarily derived from a 12Z ECMWF/GEFS/00Z ECENS blend for the second half of the forecast period, along with some previous WPC continuity. Some of the UKMET was also incorporated through Monday. Given the uncertainty in the guidance, significant changes in the forecast are possible with future updates. ...Sensible Weather... Periods of moderate to heavy rainfall can be expected from the Kenai Peninsula to the southeast Panhandle next week with onshore flow ahead of the developing Gulf system, with the potential for several inches of rain for areas with terrain enhancement. Some light to moderate precipitation is also likely for northern portions of the Interior and the Brooks range, with some of this potentially in the form of snow showers. The widespread above average temperatures and overall pleasant outdoor conditions during the short term forecast period is expected to become more autumnal as considerably cooler weather arrives in time for Sunday and early next week, particularly for central and western portions of the state. Subfreezing overnight lows are becoming more likely for the northern third of the state, and highs only in the 40s and 50s for most of the state. 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