Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 725 PM EDT Fri Sep 24 2021 Valid 12Z Tue Sep 28 2021 - 12Z Sat Oct 02 2021 ...Two More Major Storms for Alaska Next Week... ...Guidance/Predictability Assessment and Pattern/Hazard Highlights... Models and ensembles offer better than normal agreement with the stormy pattern set to continue to affect portions of Alaska into next week, bolstering forecast confidence. Accordingly, a composite of the 12 UTC GFS/ECMWF/UKMET/Canadian and the 19 UTC National Blend of Models was used as the basis for the WPC forecast days 4-6 (Tue-Thu) whose blend acts to mitigate lingering smaller scale system differences. These embedded system differences then seem best addressed by additional inclusion of larger scale compatible 12 UTC GEFS and ECMWF ensemble mean inputs for days 7 (next Fri) and especially day 8 amid faster growing forecast spread. WPC product continuity was well maintained in this manner along with some manual surface system modifications to ensure sufficient offshore storm depth/intensity consistent with a highly supportive and amplified upper flow evolution as a series of powerful closed lows/troughs work through the Bering Sea and into the Gulf of Alaska. By Tuesday into Wednesday, a deep storm system will bring a threat of high winds/waves moves into the Gulf of Alaska from the Bering Sea, allowing a southwesterly push of moisture to funnel especially into the Panhandle where rainfall amounts may be locally heavy in the valleys (and snow at the higher elevations). The next dangerous storm system out of the northern Bering will robustly dig to bring high winds/waves along with an enhanced rain/snow to western then southwestern areas of the mainland. Into later next week, as the system slams into the Gulf, another round of potentially heavy rain/snow are expected for the Panhandle and coastal areas of Southcentral. Temperatures will overall generally be below normal for the period due to the continued troughing over much of the state. Farther upstream, the JTWC still forecasts Tropical Storm 20W (Mindulle) to strengthen into a strong hurricane and start to recurve northward south of Japan by midweek. After that, the ensemble consensus takes the system to the northeast into/toward the trough to its north/northeast. This may have amplitude implications for the downstream North Pacific flow beyond the medium range period. Schichtel Hazards: - Heavy precipitation across much of the Alaska Panhandle, Wed-Fri, Sep 29-Oct 1. - Heavy precipitation along the southern coastal section and higher terrain of Mainland Alaska, Thu-Fri, Sep 30-Oct 1. 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