Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 726 PM EDT Sat Sep 10 2022 Valid 12Z Wed Sep 14 2022 - 12Z Sun Sep 18 2022 ...Gulf of Alaska system to offer a heavy precipitation threat for south-central and southeast Alaska into Wednesday/Thursday... ...Bering Sea storm heavy precipitation/winds/waves threat to reach west/southwest Alaska Thursday/Friday, then Gulf of Alaska and southern then southeast Alaska Friday/next weekend, adding tropical moisture... ...Guidance/Predictability Assessment... Model and ensemble solutions generally agree at mid-larger scales to develop potent systems both over the Gulf of Alaska and upstream over the Bering Sea Wednesday/Thursday, albeit with less uniformity with small-mid scale interactions/details over the Bering Sea and vicinity. A combination of the 12 UTC GEFS/ECMWF ensemble means and 12 UTC GFS/ECMWF seem to provide a good forecast basis for these systems during this period. Forecast spread then increases rapidly through the rest of next week across much of the Alaskan forecast domain in a pattern with ample threat potential, but lowered mid-smaller scale system predictability. Accordingly, the still compatible 12 UTC GEFS/ECMWF ensemble means were primarily used for production of the WPC product suite along with the 19 UTC National Blend of Models, but I applied manual adjustments to mitigate blend process weakening of the low, QPF/PoPs and winds to account for the potential for deeper offshore storms and the inclusion of impacts from at least the moisture from newly developed Tropical Depression Fifteen-W that is forecast to become a Typhoon over the west-central Pacific over the next few days and then enter the westerlies toward Alaska into mid-later next week as a increasingly sheared but deeply moist extratropical system. ...Pattern Overview and Weather/Hazards Highlights... There remains a strong guidance signal that ample energies associated with a deep upper level low/surface cyclone in the Bering Sea will increasingly transfer into the Gulf of Alaska and linger into/past next midweek. This will keep much of south-central and southeast Alaska wet and unsettled. Onshore winds ahead of an occluded cyclone and cold front moving through the Aleutians and into the Gulf of Alaska will transport moisture and help focus several days of rainfall, heavy at times, along the southern Coast and inland down through the Panhandle, with heavy snow in the higher elevations. Multi-day rainfall totals of 3 to 4+ inches are possible. There is an emerging guidance signal that an upstream upper low will subsequently work into the Bering Sea into Wednesday/Thursday along with a rapidly deepening surface low/frontal system. This system offers quite an increased threat of enhanced rain/waves and gale winds for maritime threats and inland across the Aleutians and then the western/southwestern mainland into Friday. The main storm threat focus will re-focus more over the northern Gulf of Alaska, the Alaskan Peninsula, Kodiak Island and southern Alaska Friday into next weekend. Activity/threat may then be further enhanced downstream with an uncertain influx of deep Fifteen-W moisture that may work rapidly from the west-central Pacific to the Gulf of Alaska and southeast Alaska into next weekend. Increased NBM QPF for this period, but the potential is higher dependent on the uncertain tropical connection. Schichtel 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