Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 752 PM EDT Thu Sep 9 2021 Valid 12Z Mon Sep 13 2021 - 12Z Fri Sep 17 2021 ...Heavy rainfall likely early next week from the Peninsula region to the Panhandle with accumulating snow possible in the higher elevations... ...Pattern Overview and Model Guidance... A strong upper level low is expected to be in place across southwestern Alaska on Monday along with a sub 990mb surface low and trailing front across the Gulf of Alaska. This low should weaken and then a second upper trough/closed low moves in from the Bering Sea by the middle to end of the week. Quasi-zonal flow aloft should be in place across the North Pacific and this leads to some model differences in terms of timing and magnitude. Of note is the 12Z ECMWF that becomes considerably more amplified over the Gulf by the end of next week compared to the CMC/GFS and ensemble means. By Friday, the CMC is indicating more of a broad upper ridge across the Gulf whereas the other guidance supports lower heights aloft. Taking these factors into account, the WPC fronts/pressures forecast was primarily derived from a multi-deterministic blend through day 5, and then mainly GFS/GEFS/ECENS/WPC continuity for days 6 and 7 and then mainly ensemble means for day 8. ...Sensible Weather... Much of southern Alaska is expected to be unsettled with multiple rounds of moderate to locally heavy precipitation. The highest totals are likely to extend from the eastern Alaska Peninsula/southwestern mainland through the southern coast and Panhandle, and this includes favored terrain over the southern mainland. In addition, lowering snow levels may bring accumulating snowfall to some of the higher mountains across southern Alaska. Flow ahead of the upper low tracking from the Bering Sea into the mainland should spread moisture northward across the remainder of the mainland but most of this precipitation should be lighter. Confidence remains lower than desired for specifics of another system that could bring an episode of rain and brisk winds across the Aleutians, Alaska Peninsula, and nearby areas by the middle of the week. The most likely scenario is for this system to track over the Aleutians/southern Bering Sea and Alaska Peninsula. Much of the southern mainland and Panhandle will see below normal high temperatures through most of next week. Clouds and moisture will maintain warmer anomalies for low temperatures over most southern locations, with greater coverage of above normal readings. Some areas in the southwest may still see modestly below normal lows and coverage of negative anomalies may expand somewhat northeastward. Hamrick Hazards: - Heavy rain across portions of mainland Alaska, Sun, Sep 12. - Heavy rain across portions of the Alaska Panhandle and mainland Alaska, Mon, Sep 13. - High winds across portions of mainland Alaska and the Aleutians, Sun, Sep 12. 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