Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 651 PM EST Fri Nov 26 2021 Valid 12Z Tue Nov 30 2021 - 12Z Sat Dec 04 2021 ...Well below normal temperatures over the west and some other Interior areas should moderate by next weekend... ...Potential for heavy precipitation along the southeastern coast and Panhandle into midweek... ...Overview... A deep upper trough aligned near the western coast of the mainland into midweek will gradually trend weaker as it progresses across the mainland and Gulf of Alaska. This trough should guide a short-range North Pacific storm along a path just east of Kodiak Island by around the start of the extended period early Tuesday and then to the southern coast of the mainland by Wednesday, bringing a period of enhanced precipitation to the southeastern coast and Panhandle. Slow movement of the upper trough will promote persistent though weaker low pressure over the southern coast/Gulf of Alaska into Friday, followed by more eastward movement. Farther west, guidance continues to show a compact system tracking through the western Aleutians on Tuesday and then descending into the Pacific. An amplified upper ridge will likely cross the Aleutians/Bering Sea during the latter half of the week with trailing dynamics then pushing a front across this region. Most guidance suggests this energy may significantly erode the the upper ridge by Saturday. Higher latitude flow should gain a little progression later in the period, helping to bring surface high pressure across the northern mainland into northwestern Canada by Friday-Saturday. ...Guidance Evaluation/Preferences... A blend of 12Z operational models from Tuesday into early Thursday followed by a transition to about half models/half means by day 8 Saturday represented the best ideas of guidance and provided generally modest changes from continuity. Models continue to display some spread and run-to-run variability for the main low forecast to be near Kodiak Island as of early Tuesday as well as a possible leading frontal wave that could reach the Panhandle. The small scale of important details keeps predictability low for specifics several days out in time, favoring a conservative average approach. This mean of operational models did show more of a hint at the leading frontal wave today while it trended weaker with low pressure along the southern coast by Thursday. Continuity is good for the western Aleutians system on Tuesday though the 12Z GFS strayed to the deep/northern side of the spread after Tuesday and there has been some divergence in recent runs for the ultimate evolution over the Pacific. Later in the period the 12Z ECMWF provided what appeared to be a very favorable adjustment versus prior recent runs--trending to less input of Arctic shortwave energy and a somewhat farther east upper trough axis from the mainland southward, more in line with the ensemble means. The preferred scenario still has low pressure evolving over the Northeast Pacific but with the axis of greatest moisture likely to stay to the south of the Panhandle. Some timing differences still exist for the upstream ridge aloft and trailing shortwave/surface front but a faster trend in the 12Z ECMWF has narrowed the gap. Operational model signals for better definition of the shortwave versus the means into day 8 Saturday favored maintaining about half weight of the models to the end of the forecast. ...Weather/Hazard Highlights... Over Southcentral and the Panhandle, arrival of low pressure into the Gulf of Alaska and then persistence along the southern coast should lead to min temperatures that are mostly above normal and highs within a few degrees on either side of normal on most days. Otherwise a majority of the mainland will likely see below to well below normal temperatures into late week, aside from a few pockets of near to slightly above normal readings over north-central areas. Coldest temperatures versus normal should be over the southwest. Eventual weakening and progression of the upper trough over the state should promote a moderating trend by next Saturday. The initial Gulf storm will bring a period of enhanced precipitation from the southern coast through the Panhandle during Tuesday-Wednesday. Highest totals should be from the eastern part of the Kenai Peninsula through the Panhandle. Expect somewhat lighter precipitation to linger over this area through the rest of the week as low pressure remains over or near the Gulf in some fashion. Early in the period the flow around the storm will produce a broad area of brisk to strong winds from the eastern Bering Sea through the northeastern Pacific. Mostly light precipitation should accompany the system tracking through the western half of the Aleutians around Tuesday. After midweek an area of precipitation and fairly strong winds will push across the Bering Sea and Aleutians ahead of a frontal system. This system will likely weaken considerably by the time it reaches the eastern Bering Sea but some of its moisture may still extend into the mainland by next Friday or Saturday. Rausch Hazards: - Heavy precipitation across portions of mainland Alaska, Mon, Nov 29. - High winds across portions of mainland Alaska, Mon, Nov 29. - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Tue-Wed, Nov 30-Dec 1. - Much below normal temperatures across portions of mainland Alaska, Mon-Tue, Nov 29-Nov 30. - Much below normal temperatures across portions of mainland Alaska, Mon-Fri, Nov 29-Dec 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