Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 657 PM EDT Thu Sep 14 2023 Valid 12Z Mon Sep 18 2023 - 12Z Fri Sep 22 2023 ...Stormy pattern continues with a heavy rain threat for Southeast Alaska to persist through next week... ...Guidance Evaluation/Preferences... The latest 12 UTC GFS/ECMWF/UKMET/Canadian model solutions have become better clustered overall for much of next week, bolstering forecast confidence. A favored composite provides good detail. However, there remains later weekend/early next week uncertainty with connection to West Pacific Subtropical Disturbance 93W and associated long fetched deep moisture plume and eastern Asian jet/system energy phasing. Growing forecast spread and uncertainty as well as worsening run to run continuity by later next week prompted transition to primarily the ECMWF ensemble mean whose higher amplitude upper flow blends better into this later time frame as an extension from model guidance than lower amplitude GEFS/NAEFS solutions. ...Pattern Overview and Weather/Hazards Highlights... There is high confidence that a very stormy weather pattern will continue next week on the heels of several potent systems this week. The next storm in the series is expected to cross from off Kodiak Island and the northern Gulf of Alaska to the Southeast Monday into Tuesday and again feature enhanced winds/waves and heavy rainfall both as maritime risk and inland with focus from southern coastal areas into especially Southeast Alaska. This system has origins from a strong east Asian jet and may also entrain long plume tropical moisture to further fuel activity in an already wet pattern, so runoff issues are possible. Farther north, predictability is closer to average that a closed upper low settled over northwest/western Alaska through early-mid next week may slowly weaken and eject eastward over the North Slope later next week. This system seems amplified enough to combine with surface system reflection to support daily unsettled conditions to include mainly light scattered precipitation in proximity of the system. Upstream of Alaska, there is also now a growing guidance signal supporting additional deep low development and track into/across the southern Bering Sea/Aleutians early next week along with an enhanced maritime risk and wrapping heavy rainfall/winds. Steady downstream deep energy transfer should lead to the potential storm and associated risks spreading into southwest Alaska/AKpen/Kodiak by Tuesday then Southcentral to Southeast Alaska by Wednesday into next Thursday. Yet another deep low in this powerhouse series may meanwhile work back upstream into the Bering Sea next Thursday/Friday that could again spread threatening weather to the the mainland, perhaps with a farther northward track/effect than the previous stream of systems. Schichtel Hazards: - Heavy rain across portions of the Alaska Panhandle and mainland Alaska, Sun-Mon, Sep 17 -Sep 18 and Wed-Thu, Sep 20 -Sep 21. - High winds across portions of the Alaska Panhandle and mainland Alaska, Sun, Sep 17. 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