Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 637 PM EDT Wed Apr 26 2023 Valid 12Z Sun Apr 30 2023 - 12Z Thu May 04 2023 ...Synoptic Overview... Through the course of the coming week a strong upper low is forecast to drop slowly southward across the Bering Sea before settling near the central Aleutians. A separate low pressure system is expected to track towards the Gulf of Alaska and reach the general vicinity of the southeast Panhandle region by Sunday, then weakening Monday and beyond. Behind that system, a separate ridge axis begins developing across the central Gulf early next week between the Aleutians low and the Panhandle low. ...Guidance Evaluation/Predictability Assessment... The latest run of the guidance continues to show some improvement in the clustering with respect to the strong low over the Bering Sea and also for the approaching low pressure system to the Panhandle/southern coast region. As with the previous runs, there continues to be some latitudinal differences with the core of the low, and some timing differences with shortwave energy pivoting around the southern periphery of that low. Yesterday there was a hint that the low may be deepening toward the end of the extended period which could impact how much/how far inland the QPF spreads- that trend did persist and most of the guidance are a few mb deeper with the low near the Bering/western Mainland by the end of the extended forecast. Preferred a general blend of the NBM,12Z/06Z GFS, 12Z/00Z ECWMF, 12Z CMC and GEFS/EC ensemble means for the forecast suite. ...Weather/Hazard Highlights... A plume of very moisture will stream onshore across the Southeast and then spread westward along the southern coast of the mainland as the mid-to-upper cyclone drops slowly across the Bering Sea. The PW values will be nearing 0.75-1 inch which is approximately 2 to 3 std. dev. above normal for the end of April/beginning of May. This steady influx of moisture and the approach of the front to the Panhandle will support a duration of moderate to locally heavy rainfall in the lower elevations and snow in the mountains. This onshore moisture flux will also modify the cold air mass inland with highs reaching 45-55 degrees for many inland areas. A multi-day total of liquid equivalent precipitation may be 3-6 inch range in orographically favored locations remain in the forecast for much of the southern Coast/Southeast. Moderate to locally heavy rain will also be possible for portions of the Alaska Peninsula and Southwest Alaska on Monday. The remainder of southern Alaska should remain unsettled overall as assorted cyclones impact the southeast Panhandle and the Alaska Peninsula. The various low pressure systems should lead to periods of gale force winds, with the possibility of some storm force gusts, across portions of the Gulf of Alaska and Bering Sea. The northern coast of Alaska also has the threat of gales late week into the weekend as the pressure gradient tightens over the region. Campbell - Heavy precipitation across portions of mainland Alaska, Mon, May 1. - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Sat, Apr 29 and Tue, May 2. 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