Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 723 PM EDT Wed Sep 20 2023 Valid 12Z Sun Sep 24 2023 - 12Z Thu Sep 28 2023 ...Overview and Guidance Evaluation/Preferences... Upper pattern over the high latitudes during the medium range will feature a very strong (~175kt) upper jet exiting off eastern Asia late this week and arcing across the Aleutians into a broad trough well south/southeast of the Gulf of Alaska. To the north, troughing over northeastern Russia will slowly settle into the western mainland with leading weak/narrow ridging squeezed into northeastern Alaska. This favors rather quiet/typical conditions over much of the 49th state with the storm track near and south of 50N. The troughing digging into the northeast Pacific west of Washington will spur cyclogenesis and a fairly deep system (PMSL values nearing minimum values for this time of year per CFSR and ERA5 climo data around 48N/135W) but with only fringe effects for the southern Panhandle. It appears that much of mainland Alaska will be under the protective shield of a ridge axis oriented just north of Alaska within a synoptic scale Rex block pattern. The 12Z guidance was in good agreement overall with expected timing/track differences in the handling of weaker waves along the baroclinic zone just south of the Aleutians. The 12Z ECMWF was very fast carrying a wave eastward through the Aleutians eastward into the Gulf of Alaska early next week. But the ensemble means (GEFS, EC, and CMC) remain in very good agreement maintaining the slow-to-evolve pattern through Day 8-- with two upper lows that have a tendency to linger over northern Bering Sea and over the Pacific just off the west coast of Canada. This led to a multi-model/ensemble blend that trended toward increased ensemble weighting by next week (Days 5-8) for the surface progs. The 19Z NBM was a good starting point for the sensible weather grids, except a lingering band of high QPF over the eastern Aleutians that is not supported by the operational models. ...Weather/Hazards Highlights... With near to below average precipitable water values over nearly the entire state for this period, so will be precipitation for the period. Little to no rain/snow is expected over the majority of the interior/mainland, with light precipitation over the Aleutians eastward across coastal Southcentral. Only the southern periphery of Alaska including the Aleutians will have some rainfall to speak of. The southern Panhandle will be more likely to see higher rainfall amounts early next week as the deep system wraps up southwest of Haida Gwaii. Temperatures are forecast to be within several degrees of typical values for late September, with highs generally in the 40s/50s and lows in the 20s/30s. Fracasso/Kong No significant hazards are expected over Alaska during this forecast period. 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