Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 801 PM EDT Tue Oct 12 2021 Valid 12Z Sun Oct 17 2021 - 12Z Thu Oct 21 2021 ...Stormy Pattern Continues from the Aleutians through Southern and Southeast Alaska... ... Guidance and Predictability Assessment... Multiple lows will traverse from the Bering Sea into the Gulf of Alaska during the extended period, which will keep stormy conditions across much of the southern parts of the state. The degree of confidence with this pattern and evolution is above average even though there continues to be some timing and variability in the details. Therefore included more weighting of the global guidance during the middle and end of the forecast than typical. The WPC Alaskan medium range product suite used the deterministic models (GFS/ECMWF/UKMET/CMC) blended with the GEFS and ECENS ensemble means. More deterministic weighting was given during the early periods with higher predictability, with more weighting towards the ensembles by the end of the period to smooth out the differences. It was noticed that the CMC and the ECWMF took the low a little further north than the rest of the guidance which suggests that parts of the Southwest may end up being a little drier. ...Pattern Overview and Weather/Hazard Highlights... An energetic and progressive flow aloft will support multiple surface low pressure systems affecting portions of Alaska late this week and into early next week. The initial low pressure system will be tracking into the Gulf of Alaska will keep increased cloud cover, gusty winds and an enhanced precipitation pattern for southern and southeast Alaska. At times, precipitation may be moderate to locally heavy across portions of the Panhandle region, with snow likely in the higher elevations of southern Alaska. Upstream flow is then expected to drive a deep storm into the Bering Sea by next weekend with downstream energy transfer allowing for triple point low developments, which should work across the eastern/central Aleutians and the AKPen region and eventually into the Gulf of Alaska by next Monday. The Aleutians will get another round of heavy rainfall and gusty winds this weekend, shifting to the southern coast/Alaskan Panhandle by early next week. The exact amounts, along with how far inland the precipitation shield extends, will be dependent on the position of the low as it enters the Gulf. This is one of the features that has spread in the guidance so specifics are less confident. Mean low pressure and cloudy/unsettled conditions across the Gulf and southern Alaska region through the period should keep temperatures below normal. Across northern and central Alaska, temperatures should be closer to normal with a period of slightly above normal temps by early next week as weak upper level ridging builds in from the east. Campbell 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 Hazards: - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Mon-Tue, Oct 18-Oct 19. - High winds across portions of mainland Alaska and the Aleutians, Sat-Sun, Oct 16-Oct 17. 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