Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 502 PM EST Mon Dec 11 2023 Valid 12Z Fri Dec 15 2023 - 12Z Tue Dec 19 2023 ...Heavy Precipitation Pattern for Southeast Alaska set to linger into Thursday... ...Guidance Evaluation/Preferences... A composite blend of best clustered guidance from 12 UTC GFS/ECMWF/UKMET and 12 UTC GEFS/ECMWF ensemble means for Friday into the weekend provides a forecast basis with reasonable detail and compromise system timing. This maintains max WPC product continuity in a pattern with near average predictability. An outlier 12 UTC Canadian seems to break Bering Sea upper trough energy too quickly through amplified downstream upper ridging into the Alaskan Interior Friday and offers less likely phasing of Arctic energies this weekend. Prefer to then switch to a blend the 12 UTC GEFS/ECMWF ensemble means later weekend through early next week in an attempt to mitigate growing system/flow uncertainties and to maintain best overall product continuity. ...Weather/Hazards Highlights... A heavy precipitation threat for Southeast Alaska supported by a locked in and amplified Gulf of Alaska upper trough position along with an associated series of deepened Gulf of Alaska lows and connected moisture feeds over the next few days is expected to gradually ease Thursday with an overall pattern transition. Elsewhere, an unsettling upper trough position should weaken but linger over the mainland later this week into the weekend to support some light to locally enhanced snow. Upstream, amplified upper trough/closed low energies will work steadily eastward through the Bering Sea and Aleutians Friday through the weekend as a leading/blocking upper ridge/trough couplet shifts eastward and weakens. This transition would allow for less certain details of northern Pacific/Aleutians and Bering Sea traversing systems to bring organized precipitation generally eastward across these areas and then increasingly to the mainland over this period and into early next week. This could support a moderately snowy pattern for Western Alaska and into the Interior. Ample upper energies will meanwhile undercut and break downstream to renew Gulf of Alaska upper troughing and provide a conduit for uncertain flow embedded systems to progress and re-develop. This pattern would offer renewed potential for periodic and growing over time opportunities for locally enhanced precipitation and winds for Southern to Southeast Alaska to monitor given focus there over the next few days. 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