Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 705 PM EST Tue Feb 28 2023 Valid 12Z Sun Mar 05 2023 - 12Z Thu Mar 09 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... Precipitation may linger across the Southeast this weekend as a trough aloft and a low pressure system in the Gulf of Alaska continues to weaken. 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. The weather pattern will quickly transition to an amplifying ridge over much of the mainland through early next week. With the ridge in place, approaching storms will 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... The latest runs of the global guidance and their ensemble means continue to have good agreement with the large scale pattern and evolution though most of the extended period and initially with a surface low pressure 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. The main feature from the end of the weekend through at least midweek (end of the extended period) will be the ridge, building across the Aleutians and Bering Sea and shifting into the mainland over the weekend, with Bering Sea troughing behind. As with the last few runs, there continues to be some 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). WPC utilized a combination of the 12Z ECMWF/GFS/CMC/UKMET initially to maintain forecast continuity, before omitting the UKMET and including the NAEFS and EC ensemble means. ...Weather/Hazards Highlights... Northwest of the mean Gulf low, high winds are a concern around 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. Localized heavier snow possible for portions of the western/northwestern Alaska. 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. Campbell/Tate Hazards: - Heavy precipitation across portions of the eastern Aleutians, Sun-Mon, Mar 5-Mar 6. - Heavy snow across portions of western Alaska, Sun-Mon, Mar 5-Mar 6. - High winds across portions of the Alaska Peninsula into the Kenai Peninsula and the Kodiak Island, Fri, Mar 3. 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