Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 547 PM EDT Sat Sep 12 2020 Valid 12Z Wed Sep 16 2020 - 12Z Sun Sep 20 2020 ...Heavy rain likely next week for southwestern/southern Alaska... ...Overview and Guidance/Predictability Assessment... Deep upper low will slowly progress through the Bering Sea next week with additional shortwave spokes rotating around the circulation. Lead surface front into western areas will weaken in advance of a surface wave out of the North Pacific late Wednesday. This low will likely deepen and track toward the AKPEN by early Thursday. The 12Z deterministic models generally agreed on the synoptic pattern with the UKMET again the apparent outlier. The ECMWF/GFS took a more NW/SE track (respectively) around the AKPEN but a blend of these with the Canadian seemed to get a plausible solution with the main low into SW areas but triple point development near Kodiak toward the southern Kenai peninsula early Friday. Ensembles keep this front progressive into Canada with another surface front driven by a shortwave out of northeaster Russia drives a cold front across the Aleutians. This may round the base back to the Gulf next weekend with another system from the N Pacific perhaps moving through the western Aleutians next Sunday. Ensembles were rather agreeable throughout with the GFS/ECMWF near enough to allow for a majority deterministic weighting to next Sat. This kept good continuity overall. ...Weather/Threats Highlights... Periods of rain will accompany the lead cold front, with modest amounts possible over Southcentral (especially south-facing areas of the Kenai Peninsula). By Thursday, potential exists for much more rain along the southern coast from the AKPEN/Kodiak through the Kenai Peninsula into Prince William Sound. Ensembles indicate the possibility of several inches of rain Thu and Fri (each) with a surge of moisture from the south. This could be enhanced by triple point development just off the coast per the GFS. Multi-day rainfall totals may approach 10 inches in favored areas. Pattern should turn more showery after the system moves northeastward/eastward into/past the Panhandle late Friday. Max temperatures near to above normal over the Interior will trend a bit cooler with time as the upper low and colder temperatures aloft filter in. Max temperatures over southern coastal areas will generally be near to below normal through the period. Min temperatures will be near to above normal through the period. Fracasso Additional 3-7 Day Hazard information can be found on the WPC medium range hazards 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