Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 630 PM EDT Tue Oct 17 2023 Valid 12Z Sat Oct 21 2023 - 12Z Wed Oct 25 2023 ...Synoptic Overview... The synoptic pattern over Alaska this weekend through the middle of next week is expected to initially feature upper level troughing across much of the Mainland, as the low pressure system bringing unsettled weather to the Southeast Alaska region winds down by late Thursday into early Friday. In its wake this weekend, generally cooler than normal temperatures and relatively lighter precipitation is expected. By early next week, a stronger storm system will approach the Bering Sea and far eastern Russia, bringing widespread precipitation to parts of the western and northwestern Mainland. ...Guidance Evaluation and Preferences... In general, the 12Z model guidance was in relatively good agreement with the major synoptic features and associated sensible weather impacts such that for Days 4-6 (Sat to Mon), a near equal weighted blend of the available deterministic guidance was applied (ECMWF, GFS, CMC, and UKMET). By early to mid next week (Days 7-8), there is some timing, location, and strength differences with the area of low pressure moving through the Bering Sea, eastern Russia, and parts of the Chukchi Sea. The GFS is a bit further south compared to the ECMWF, settling the area of low pressure over the northwest Mainland through the end of the period. This is mainly due to the difference in the upper levels over the Arctic Ocean with the potential development of an upper trough (GFS) or not (ECMWF). So, the predictability and confidence really lowers by Day 7 and Day 8, especially across the western/northwest Mainland. For these reasons, while the earlier portion of the period used a near equal blend of the deterministic guidance, the Day 7-8 blend relied heavily on the ensemble means from the GFS and ECENS, accounting for over 50% of the blend by next Wednesday. ...Weather and Hazards Highlights... In the wake of the heavy rain event across the Southeast Alaska region, upper level troughing will prevail across much of the Mainland this weekend. This will bring generally cooler than normal temperatures and relatively lighter precipitation (or dry conditions), with interior highs below freezing and overnight lows dropping into the teens and 20s, lower in the colder spots. Attention then turns to the storm system expected to brush parts of the state early to middle next week. An area of low pressure will cross through portions of the Bering Sea, clipping eastern Russia before reaching into the Chukchi Sea. It will spread precipitation across much of the western to northwest Mainland, including the potential for widespread measurable snowfall. Though, details on amounts and potential weather hazards are still uncertain this far out given some of the forecast model uncertainty. Taylor 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