Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 706 PM EDT Sun Sep 05 2021 Valid 12Z Thu Sep 09 2021 - 12Z Mon Sep 13 2021 ...Pattern Overview and Model Guidance... The latest suite of model and ensemble guidance continues to show very good agreement on the overall large scale synoptic pattern through much of the Alaska extended range period which features a broad upper level low which should drift southward across the Bering Sea. Several shortwaves look to rotate through the base of the upper low sending a couple of low pressure systems near the Aleutians and into the Gulf/Mainland region. The first low, which could become a fairly deep cyclone (several solutions suggesting a central pressure near 980mb) should slide south of the Aleutians and into the Gulf Thursday and Friday. Guidance shows enough agreement to warrant an equal blend between the 12z GFS, ECMWF, and CMC, but even the deterministic solutions still struggle somewhat on exact location. After day 5, the guidance becomes increasingly chaotic with the details of additional shortwave perturbations and surface low pressure systems. Thus, the WPC blend trended quickly towards the ensemble means which helped mitigate these smaller scale uncertainties, while maintaining modest amounts of the 12z GFS/ECMWF just for added system definition. This drives a second cold front through the Alaska Peninsula/southern coast on Sunday, reaching the Panhandle by next Monday. ...Sensible Weather... Moderate to locally heavy rainfall will accompany the first surface low as it drifts through the Gulf from the AK Pen/Southern Coast into the Panhandle Thursday-Saturday. Expect marine hazards and gusty winds to also impact parts of the coast, the strength of which highly dependent on exact location of the low in the Gulf. A cold front moving through western Alaska will also bring precipitation as well, especially for terrain areas, with some precipitation in the form of snow. As this interacts with the next shortwave south of the Aleutians next Sunday, another round of moderate to locally heavy rain is likely for southern Alaska and the Panhandle, with precipitation particularly enhanced over the terrain. Thursday may be particularly warm for parts of northern and eastern Alaska, but should trend back towards or below normal by early next week. Across the Panhandle and southern half of Alaska, general cloudiness and unsettled weather should keep temperatures near or below normal through the entire period. Morning lows however should remain above normal through next weekend for most of the state. Santorelli 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