Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 737 PM EDT Thu Sep 23 2021 Valid 12Z Mon Sep 27 2021 - 12Z Fri Oct 01 2021 ...Overview and Guidance/Predictability Assessment... Active pattern will continue across the high latitudes as upper ridging remains mostly in place between the Hawaiian islands and the Aleutians. This favors continued/renewed troughing into the Gulf of Alaska via the North Pacific as well as the Arctic (out of northeastern Russia). With a rather steady pace and a Goldilocks state in between fast/unsteady zonal flow and amplified/blocked flow, the 12Z models/ensembles showed good agreement to start the forecast period Mon-Wed next week. System in the southern Bering will track eastward into the Gulf as its attendant fronts push into the Panhandle and British Columbia. At the same time, an upper low will drop southeastward out of northeastern Russia/East Siberian Sea toward the Bering Strait and eventually the Gulf, per the ensembles. As it exits Russia, the deterministic models diverge in speed/track of the upper and surface lows, complicated by energy streaming eastward out of Kamchatka into the southern portion of the upper low. Given the lead time and several features involved, opted to rely increasingly on the ensemble means (GEFS and ECMWF ensembles) as both were close to each other through the period. Farther upstream, the JTWC 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 implications for the downstream North Pacific flow beyond the medium range period depending on its interaction with the upper trough. ...Weather Highlights... Light to modest rain will spread across the eastern Aleutians Monday in advance of the Bering system, with breezy conditions around the low center. Exiting system near Haida Gwaii will support some showers for the Panhandle to start the week. By Tuesday into Wednesday, the Bering system will move into the Gulf, allowing a southwesterly push of moisture to funnel into the Panhandle where rainfall amounts may be locally heavy in the valleys (and snow at the higher elevations). Next system out of the northern Bering will bring additional rain/snow to western areas of the mainland. By late next week, as the system slips into the Gulf, another round of rain/snow will be possible for the Panhandle and coastal areas of Southcentral. Temperatures will generally be below normal for the period due to the continued troughing. Readings may be 5-15 degrees below normal, especially over the Alaska Range, with max temps in the 20s over the North Slope/Brooks Range, 30s/40s over the Interior, and near 50 closer to the coast. Fracasso Hazards: - Heavy precipitation across much of the Alaska Panhandle, Wed-Thu, Sep 29-Sep 30. 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