Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 650 PM EST Fri Dec 13 2024 Valid 12Z Tue Dec 17 2024 - 12Z Sat Dec 21 2024 ...Deep low to produce a high wind threat from the southern Bering Sea through the Aleutians into early next week... ...Overview/Guidance Evaluation/Preferences... The upper levels of the 12 UTC models are quite well clustered through next week. A deep upper level low moving east along the Aleutians this weekend will stall out near the Eastern Aleutians. Downstream ridging will build over the Yukon and British Columbia, occasionally intruding into northeast Alaska. Thus, much of the mainland of the state remains in broad south to southeasterly flow through the week. As this pattern is slow-changing and relatively steady-state, this lends confidence to the forecast for largely unsettled weather for much of the state, especially southern Alaska and the Panhandle, and steadily warming temperatures from this weekend's brief cold snap right through the week. A deterministic blend of the GFS, EC, and CMC was used for days 4 and 5 (Tuesday and Wednesday), with the UKMET phased out quickly for being an outlier from the consensus of the aforementioned blend. For late week, a blend with the GFS and EC ensemble means was used which generally smoothed out the smaller and largely unpredictable shortwaves in favor of the broader longwave trend of ridging across northern Alaska and a nearly stationary upper level longwave trough over the Bering and Aleutians. Frequently occluding lows passing well south of the Aleutians will make a hard left turn northward into the Gulf, resulting in rapid weather changes across much of the southern half of the state through the week. ...Weather/Hazards Highlights... A deep Arctic air mass and associated polar front will halt their advance and slowly retreat eastward into Canada through next week. Temperatures will moderate from lows in the -10s to -20s in the Interior starting Monday, eventually warming into the 20s and 30s above for highs by Thursday. As a vertically stacked low over the western Bering moves eastward, it will tap into a hyperactive jet stream over the north Pacific, resulting in multiple rounds of cyclogenesis first over and south of the Eastern Aleutians and eventually spreading into the Gulf. The strongest lows will be over the Aleutians and southern Bering, where a high wind threat remains in the hazards as winds especially through the gaps in the Aleutians exceed 50 kt early next week. As the lows track north into the Gulf by midweek, the threat will become heavy valley rains and mountain snows into the Panhandle and into the Kenai Peninsula, Kodiak Island, and portions of the Aleutian Range. While the upper level pattern is high confidence through the week, the details of any shortwaves rounding the broader upper level trough over the Aleutians remain highly uncertain. Thus, the confidence for hazardous weather is fairly low. Strong gap winds from the cold that will settle over the state this weekend will persist through Prince William Sound and the Panhandle, and these will abate by midweek in exchange for strong southeasterly gap winds through the typical barrier jet areas of eastern Prince William Sound, Turnagain Arm, the Barren Islands and Southern Cook Inlet, and Shelikof Strait. Finally, deep Arctic air and cold advection will impact far northwestern Alaska, the Bering Strait, and St Lawrence Island. Heavy freezing spray will remain an ongoing concern right through next week in these areas as the sea ice edge advances southward. Wegman Additional 3-7 Day Hazard Information can be found on the WPC medium range hazards outlook chart at: The WPC Hazards Outline depicts these threats. 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