Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 601 PM EST Mon Nov 25 2024 Valid 12Z Fri Nov 29 2024 - 12Z Tue Dec 03 2024 ...Wet/Snowy pattern setting up for the Southeast/Panhandle by the Thanksgiving weekend as frigid air prevails across the Interior... ...Guidance Evaluation/Preferences... Model guidance continues to agree that a blocking omega upper-level pattern across the Alaskan domain will become more amplified with time heading into the Thanksgiving weekend. A closed anticyclone is forecast to form and meander over northeastern Siberia while a general storm track extends from south of the Aleutians toward the Southeast/Panhandle through the medium-range period. More specifically, today's deterministic guidance has again trended toward a stronger ridge axis across the Bering Sea through the Alaska Peninsula at the start of the medium-range forecast period midweek. This stronger ridge appears to help slowing down the northeastward progression of cyclonic circulations along the aforementioned storm track, and delay the arrival of precipitation across the Panhandle during the weekend. The ridge axis then detaches into an upper high which meanders over northeastern Siberia into early next week. Meanwhile, deterministic guidance today shows increased uncertainty regarding the details of the individual disturbances in the vicinity of the storm track. The ensemble means generally depict that the leading cyclone that is forecast to track south of the Aleutians late this week will slow down and weaken as it edges toward the southern coastline and the Panhandle early next week. There is a tendency for the models to slow down this system further as the upper blocking pattern gets established over the Alaskan domain. Ensemble means then show good agreement that the next cyclone moving along the same storm track will reach south of the Aleutians by next Tuesday. Today's WPC forecast package for Alaska was based on a consensus blend of about 40% from the 12Z ECMWF and the 00Z/12Z EC mean, 40% from the 12Z GFS/GEFS, and 20% from the 12Z CMC/CMC mean, transitioning to mostly a blend of the ensemble means for Days 7 & 8. This blend yielded a solution compatible with yesterday's forecast package, resulting in further lessening of and later arrival of QPF for the Panhandle during the Thanksgiving weekend. ...Weather/Hazards Highlights... Persistent northwesterly flow in the upper levels down the right branch of an omega blocking pattern will maintain mostly clear and cold conditions for interior Alaska with a cold high pressure system lifting north into the Arctic Ocean into a ridge axis at the surface. Passing shortwave energy could develop a front and bring some snow showers for the North Slope late this week. Much of the interior sections will be colder than normal, with low temperatures possibly dipping to near or below -40 degrees at the coldest spots in the eastern interior. Milder than normal temperatures are forecast for the North Slope as a more southwesterly flow develops at the surface. Modest amounts of precipitation associated with a weakening old cyclone remain across the Panhandle as the medium-range period begins midweek. Meanwhile, the distance from the main cyclone moving across the North Pacific will likely keep the heaviest precipitation from reaching the Aleutians, although a couple of days of light to moderate rain under gale-force east to northeasterly winds can be expected across the southern Peninsula to the eastern Aleutians by around Thanksgiving. An increasing chance of mountain snow and low-elevation rain can be expected to overspread the Panhandle through the Thanksgiving weekend. Precipitation should become heavier early next week as the offshore cyclone edges closer toward the Panhandle and the southern coastline although the details remain uncertain at this juncture. Kong 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