Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 455 PM EST Thu Dec 01 2022 Valid 12Z Mon Dec 05 2022 - 12Z Fri Dec 09 2022 ...Guidance/Predictability Assessment and Preferences... The guidance shows general agreement concerning the general flow pattern in and around AK, but detail issues are larger than previous days. A large and deep upper level vortex over Siberia broadens eastward with time, eventually enveloping AK. The 12z UKMET is the closest to western AK with a cyclone moving by on Sunday, so used a very small percent of that guidance. The area of better model agreement was in and near the AK Panhandle. The same is not true in the Aleutians, where the 12z UKMET/ECMWF support the idea of a deep cyclone moving through the area into the Bering Sea. However, the GFS is delayed in its arrival and the 12z Canadian is the most out of tolerance with the other guidance. Considering the uncertainty, for the 500 hPa heights, pressures, fronts, and winds, generally used a deterministic heavy blend of the 12z GFS, 12z ECMWF, 12z UKMET, and 12z Canadian early on before including up to 60% of the 12z NAEFS mean/00z ECMWF ensemble means thereafter with tweaks made (lower pressures and increase winds) so that systems weren't so washed out. This idea maintained reasonable continuity with Wednesday's forecast. The QPF used the 19z NBM and, 12z GFS, and 12z ECMWF solutions. The remainder of the grids were 19z NBM weighted, as usual. ...Weather/Hazards Highlights... A pair of robust storm systems track into the Bering Sea early on. ECMWF EFI depicts rather anomalous wind speed values from the AK Peninsula on north along the western coast of Alaska. Meanwhile, the northern coast of Alaska will be caught between a strong surface high building over far northern Canada and northern Greenland, while a cluster of deep cyclones spin over northeast Russia. This results in a tight pressure gradient positioned near the most northern tier of Alaska. This allows for unusually strong wind gusts to linger the first few days of the medium range period. These storms entering the Bering Sea will also bring a steady dose of anomalous Pacific moisture to western and southern Alaska. There are elevated locations along the Seward Peninsula and farther northeast that remain favored upslope locations for heavy snow. A freezing rain threat remains from Galena on north to areas just north and east of Point Hope where hazardous ice accumulations are expected. These storm systems will deliver heavy precipitation along the AK Peninsula Saturday into Sunday, then towards Kodiak Island Sunday into next Monday. While there is some elevated spread in model guidance on timing and amounts, the signal for the surge of deep Pacific moisture is present for heavy precipitation potential throughout the Ak Panhandle next Monday into next Tuesday with coastal/valley rain and heavy mountain snow. From next Tuesday into next Wednesday, the Kenai Peninsula and on east towards the AK Panhandle should rain heavily. Roth/Mullinax Hazards: - Heavy precipitation across portions of mainland Alaska, Sun-Tue, Dec 4-Dec 6. - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Tue-Wed, Dec 6-Dec 7. - Heavy snow across portions of mainland Alaska, Sun-Mon, Dec 4-Dec 5. - Freezing rain across portions of northern mainland Alaska, Sun-Mon, Dec 4-Dec 5. - High winds across portions of mainland Alaska, Sun-Tue, Dec 4-Dec 6. - High winds across portions of the Aleutians, Sun-Mon, Dec 4-Dec 5. 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