Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 700 PM EDT Mon Sep 06 2021 Valid 12Z Fri Sep 10 2021 - 12Z Tue Sep 14 2021 ...Multiple rounds of heavy rainfall likely from the Peninsula region to the Panhandle with accumulating snow possible in the higher elevations... ...Pattern Overview and Model Guidance... The weather pattern across Alaska should remain quite active through the extended range as a mean upper level low meanders in the Bering Sea through the weekend before eventually pushing east into the western Mainland early next week. Shortwaves rotating through the base of the trough will send a couple of surface low pressure systems eastward through the Gulf and into western North America. The latest suite of model and ensemble guidance continues to show very good agreement on the overall large scale synoptic pattern, especially through about day 6. After that, details of individual systems becomes a little more uncertain, especially regarding possible low pressure into the Mainland as well as the next system coming into the western Aleutians by next Tuesday. The 12z GFS and ECMWF show fairly good agreement through the period with the ensemble means, with the typical question on timing of systems as you go later in the period. The WPC forecast relied on a majority deterministic solution through day 6, trending towards the ensemble means late period to mitigate some of the differences. This maintains excellent continuity with yesterdays forecast as well. ...Sensible Weather... Moderate to locally heavy rainfall will accompany a deep low pressure system present in the Gulf of Alaska on Friday as Pacific moisture streams northeastward ahead of the cold front. Models suggest the potential for several inches of rainfall along the southern coast and the Panhandle region on Friday into Saturday with local enhancement likely along favorable mountain ranges. Marine hazards and coastal gusty winds are also likely from roughly the Kenai Peninsula to the Panhandle coast. Behind this system, the upper low in the Bering Sea moving into the Mainland this weekend will bring another low pressure system along the Aleutians and eventually into southeast Alaska by next Monday. Another round of heavy rainfall is possible Sunday-Tuesday for the Peninsula-Southern Coast-Panhandle region, with precipitation also likely farther inland across southwestern and interior Alaska as well. Lowering snow levels may bring accumulating snowfall to some of the mountains across southern Alaska. The north slope region of Alaska should remain dry through much of the period. Temperatures across northern and eastern Alaska will be above normal on Friday but should trend back below normal through the weekend as the upper low moves closer to the region and heights lower across the state. Elsewhere, clouds and precipitation should keep temperatures near or below normal the entire period. With the exception of parts of the southwest, morning lows across all of Alaska should remain above normal through next weekend and into early next week. Santorelli Hazards: - Heavy rain across portions of mainland Alaska, Thu, Sep 9 and Sun-Mon, Sep 12-Sep 13. - Heavy rain across portions of the Alaska Panhandle and mainland Alaska, Fri, Sep 10 and Sun-Mon, Sep 12-Sep 13. 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