Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 657 PM EST Mon Feb 27 2023 Valid 12Z Fri Mar 03 2023 - 12Z Tue Mar 07 2023 ...A pattern change early next week to a mainland upper ridge will result in Aleutians/western mainland precipitation and winds, milder temperatures for the mainland, and a cold and drier trend for the Panhandle... ...Overview... For the latter part of this week, a trough aloft and a weakening low pressure system in the Gulf of Alaska will help produce some precipitation over the Panhandle, though the heaviest amounts are likely to be in the short range period. Gusty to high winds are possible on the backside of the low, in favored gap wind areas of the Peninsula into Kodiak Island and the Kenai Peninsula along with the surrounding waters and islands. By next weekend, a significant pattern change is expected, as upper ridging looks to move into the Aleutians first and then set up across the mainland through early next week. This should direct the storm track across the Aleutians and western Alaska and cause initially colder than average temperatures to moderate over the mainland while the Panhandle can expect colder conditions. ...Model Guidance/Predictability Assessment... Model guidance continues to show reasonably good agreement today with the larger-scale features throughout much of the forecast period. As the period begins Friday, surface low pressure has good model consensus in the Gulf of Alaska, while the track/strength of a trough in the upper levels shifting eastward is generally agreeable despite some uncertainty whether there will be an embedded closed low within it or not. Then the upper ridge will become the main feature across the state, first building across the Aleutians and Bering Sea and shifting into the mainland over the weekend, with Bering Sea troughing behind. There are some mainly minor timing and amplitude differences in the ridge as shortwave energy rounds it, mostly well within reason of typical spread at the mid-late medium range time frame. One such difference affects the positioning of a far eastern Canada surface low shifting northeastward on Saturday, but timing with a low moving north-northeastward from the Pacific crossing the Aleutians and moving into the Bering Sea is fairly agreeable this weekend. By Monday-Tuesday, the GFS and CMC suites of guidance indicates the north-south axis of the ridge a bit more to the east than the ECMWF and EC mean that maintain it west. There is potential for some energy to suppress the western/northern parts of the ridge and push the axis eastward, but at this point it seems prudent to lean toward a middle ground solution of the ridge axis and the extent the ridge maintains itself on the western side (which affects how far eastward into the mainland precipitation is able to make it as well). Thus the WPC forecast was based on a blend of the deterministic 12Z ECMWF/GFS/CMC/UKMET initially, with more gradual incorporation of the ensemble mean guidance to about half by the end of the period for a compromise position of the ridge axis and extent. ...Weather/Hazards Highlights... Low pressure at the surface in the Gulf of Alaska and a mean upper trough will provide support for precipitation (mainly snow) to linger across the Panhandle late this week, though with lighter amounts than in the short range period. Northwest of the mean Gulf low, high winds are a concern around Thursday-Friday across the Alaska Peninsula eastward into Kodiak Island and the Kenai Peninsula with strong offshore flow. A drying trend is likely across the Panhandle by the weekend as upper ridging moves into the mainland, directing cold and dry northerly flow into the Panhandle on the east side of the ridge. Meanwhile western Alaska can expect more active conditions for next weekend as low pressure and frontal systems could affect the Aleutians into the western mainland, on the western side of the ridge and ahead of a Bering Sea trough. While some details remain uncertain, precipitation and winds will likely be enhanced at times in the Aleutians to Alaska Peninsula as a surface low tracks across. At least the western mainland is likely to see precipitation chances increasing early next week along with some gusty southerly winds, but there remains low confidence in how far east this activity will spread. Temperatures across the Panhandle are likely to be below normal in terms of highs for the latter part of this week. Lows and highs should continue to drop considerably there into next weekend given northerly mean flow ahead of the upper ridge as well as cold continental flow at the surface, for anomalies around 10-20F below average. Over the mainland, an initially progressive pattern will lead to a temperature swing from colder to warmer than normal temperatures. Cooler than average temperatures by 10-30 degrees are forecast to shift from the southwestern mainland Friday into the southeastern mainland Saturday with the bout of upper troughing. But as the upper ridge builds in, well above normal temperatures will first affect the western part of the state over the weekend, reaching much of the mainland by Monday-Tuesday. Some highs above freezing look probable across the Alaska Peninsula and into the southwestern mainland, while the North Slope may see the highest anomalies with some temperatures 30+ degrees above normal. Tate 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