Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 753 PM EDT Sat May 06 2023 Valid 12Z Wed May 10 2023 - 12Z Sun May 14 2023 ...Large Gulf of Alaska storm pattern all next week... ...Overview... Through much of next week into next weekend, the main weather feature of note will be a large and deep layered mean low pressure system that should settle across the Gulf of Alaska/northern Pacific and stall due to a potent upper ridge in Canada. This will cause unsettled weather across the southern coast of Alaska as impulses wrap moisture around the maritime low, with enhanced onshore precipitation and gusty winds from Southcentral spreading into Southeast late week. Another impulse moving through the Bering may lead to a round of rain across the Aleutians/Alaska Peninsula by next weekend. ...Guidance Evaluation/Predictability Assessment... Recent model agreement remains quite good through much of the period, for above normal forecast confidence and continuity. Models indicate a persistent upper low over the Gulf/northeast Pacific, and even show reasonably good consensus for surface low positions through mid- to late week that could include lows spinning in a Fujiwhara effect interaction. Meanwhile a quick bout of upper ridging looks to form atop the Aleutians, with generally just a col pattern over the mainland. A blend of the 12Z deterministic guidance was used for the WPC forecast for days 4-6 given the good agreement without particular outliers. This trended toward slower arrival of the bulk of moisture into Southeast AK compared to the previous forecast as low positions shift. The latter part of the medium range period next weekend shows more spread arising, though nothing too extreme for this lead time. The positioning of the main upper low diverges a bit, with the 12Z CMC splitting the energy and creating perhaps a southwest outlier compared to other guidance. This position also depends on another upper low feature crossing the Bering Sea that shows some timing and track differences. Namely the GFS suite was a bit fast to bring this feature eastward compared to the non-NCEP guidance, the 12Z GEFS mean even more so than the GFS. Blended in increasing proportions of particularly the EC ensemble mean as the forecast progressed and models diverged. ...Weather/Hazard Highlights... The upper low pattern in the Gulf/northeast Pacific will provide opportunities for surface lows and frontal systems to move through and spread moisture into southern parts of the state, along with possible gusty winds wrapping as gap winds with a northern component behind the low for the Aleutians and AK Peninsula, with some enhanced easterly winds possible into Peninsula and Kodiak Island into Southcentral Alaska. The latter will favor precipitation enhancement for terrain in those areas, leading to likely the highest multi-day precipitation totals there, with likely higher elevation snow and coastal rain periodically lasting for much of next week. Farther east, precipitation chances should increase across Southeast Alaska late next week into next weekend, enhanced as potent systems lift/wrap on the eastern periphery of the main low centroid position. By next weekend, another low/frontal system moving across the Bering Sea could spread rain to the Aleutians and the Alaska Peninsula. The mean low dominating the northern Pacific should lead to below normal highs across the southern coast of Alaska, but lows should be closer to normal. Farther north should see a mix of above and below average temperatures. This means highs in the 50s and 60s for the Yukon Flats and Interior, serving to help rivers break up, but fortunately not at a terribly fast pace without well above average temperatures and with little precipitation. Tate 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