Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 729 PM EDT Mon Aug 12 2024 Valid 12Z Fri Aug 16 2024 - 12Z Tue Aug 20 2024 ...Bering Sea Storm Heavy Rainfall/Wind Threat for Western to Interior Alaska/Brooks Range Thursday/Friday... ...Heavy Rainfall Threat for the Southern Alaskan Tier/Alaska Range Thursday into the Weekend†...Deep Extratropical Low from current West Pacific Tropcial Storm Ampil may threaten Aleutians in a week... ...Guidance Evaluation/Preferences... A composite of best clustered guidance from the 12 UTC GFS/ECMWF/Canadian seems to offer reasonable detail Friday into Saturday, but it seems more prident to then quickly switch to best compatible guidance from the GEFS/ECMWF/Canadian ensemble means through longer time frames amid growing uncertainties. ...Weather/Hazards Highlights... Guidance continues to strongly herald a highly stormy/complex and transitional pattern over the next week. Forecast spread and predictability has improved for later this week with a leading storm in this forecast period forecast to develop and track up through the Bering Sea to the Arctic Ocean that may significantly impact Western to Interior Alaska and the Brooks Range. This storm offers a maritime/coastal wind/wave threat with inland impacts to include heavy rainfall/runoff issues and potential for Chinook winds off the Alaska and Brooks Ranges. Forecast uncertainty quickly grows heading into the weekend with subsequent moist systems to potentially work into the Gulf of Alaska that offer a potential threat over the Alaskan southern tier. Pacific and more northern stream energy interactions and overall progressive nature of the transitional flow remain guidance challenges. Model cycle to cycle continuity has been less than stellar, but the overall pattern seems favorable for progression of the focus for later week to weekend heavy rainfall/runoff issues from the Alaska Peninsula/Kodiak Island through SouthCentral and the Alaska Range, possibly working later into the Southeast. Meanwhile upstream, there is some continuity into early next week with a deep extratropical low track toward the Aleutians and Bering Sea in about a week to monitor. This system originates from current west Pacific Tropical Storm Ampil, and these types of transitions often lead to quite a wet and windy storm. Schichtel 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