Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 656 PM EST Tue Dec 05 2023 Valid 12Z Sat Dec 09 2023 - 12Z Wed Dec 13 2023 ...Pattern Overview and Guidance Evaluation/Preferences... The medium range period over Alaska features a main upper low meandering across/near Southwestern Alaska as a couple of shortwaves rotate around the southern periphery. A blocky ridge over the Western Bering should act to force systems to the south and into the northern Pacific and Gulf of Alaska. By the end of the period/next Wednesday, an upper ridge looks to build over Western Canada/Southeast Alaska. For the most part, the models show good agreement on the larger synoptic scale, but plenty of uncertainty in the details/timing of individual shortwaves which would have sensible weather impacts such as wind and rain along the Southern Coast and Southeast Alaska. On Saturday, a stronger surface low off the Panhandle shows some notable location differences with the ECMWF the farthest north (bringing it into northern Panhandle/Southeast AK) and the GFS farthest south into the far southern tip of the Panhandle. A general model compromise seems best to handle this feature and results in a nice middle ground placement, closest to that of the 12z deterministic CMC. Around Sunday-Monday next week, a pair of systems look to track south of the Aleutians and an eventual deepening surface low into the Gulf by the middle of next week. The models agree on the end game, but disagree on how to get there. The GFS seems to want to strengthen the second/western low over the more north low, but the ECMWF and CMC show that southern low weakening in favor of a strengthening upper system. Given the relatively smaller scale of these features, the ensemble means aren't doing well right now to resolve those differences and rather just show a deeper surface low lifting from the northern Pacific into the Gulf. The WPC forecast for today used a 75 percent blend of the deterministic solutions with 25 percent of the ensemble means for days 4 an 5. After this, gradually increased more of the ensemble means as the spread increased, reaching 60 percent of the blend using the ensemble means by day 8. For the most part, this maintains pretty good agreement with the previous WPC forecast as well. ...Weather/Hazards Highlights... The initial surface low near the Panhandle should bring a period of gusty winds and moderate to locally heavy precipitation to the region on Saturday. Generally unsettled showery conditions will continue through the rest of the weekend as mean southerly flow brings moisture into South/Southeast Alaska with precipitation increasing across the central/eastern Aleutians and the Peninsula region as a couple more surface lows drift to the south. Increased moisture will be directed into the Southern Coast of Alaska ahead of a developing surface low in the Gulf bringing a threat for more widespread heavier precipitation. Precipitation should also increase across the Alaska Range and farther north into the interior for some possible accumulating snows and local gusty winds. A colder trend is likely as the medium range period progresses, especially across the Alaska Peninsula into much of the Mainland where the core of the cold upper low sets up. Below average temperatures by 10-20F for highs will expand from the Lower Kuskokwim region and Alaska Peninsula late week farther into the Western Interior (in moderated form) early next week. The exception to this will be across the North Slope where daytime highs should be above normal the entire period. By next Tuesday and Wednesday, temperatures look to trend much warmer across Southeast and East-Central Alaska as an upper level ridge begins to build over far western Canada. Santorelli 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