Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 801 PM EDT Wed Oct 13 2021 Valid 12Z Mon Oct 18 2021 - 12Z Fri Oct 22 2021 ...Stormy Pattern Continues from the Aleutians through Southern and Southeast Alaska... ... Guidance and Predictability Assessment... Model guidance continues to have above average predictability with the evolution of multiple waves crossing the Bering Sea into the Gulf of Alaska. This pattern will be favorable for stormy conditions for much of the southern parts of the state through the extended period. The latest runs of the ensemble means are now closer to the ECWMF and CMC solutions and overall are in pretty good agreement. 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. ...Pattern Overview and Weather/Hazard Highlights... The mean low pressure pattern over the Aleutians and Gulf will keep cloudy/unsettled conditions through the extended period. In addition, the daily temperatures are expected to remain below normal. Temperatures across the northern and central parts of the state will 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. Gusty winds along with scattered to widespread precipitation is expected across the Aleutians, southern and southeast portions of the state through 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. There will be periods where moderate to locally heavy rain is expected for the Panhandle, 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 AK Pen 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. 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-Wed, Oct 18-Oct 20. - Heavy precipitation across portions of mainland Alaska, Sun, Oct 17. - 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