Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 647 PM EST Thu Dec 30 2021 Valid 12Z Mon Jan 03 2022 - 12Z Fri Jan 07 2022 ...Overview... Guidance is continuing to show a blocky pattern as initial Bering Sea into Arctic upper ridging likely closes off a high early in the week, with the high center drifting over or near eastern Siberia through the rest of the week. The Arctic portion of the ridge may rotate southward into and through the mainland enough to yield more northerly flow over the mainland by next Friday. Meanwhile there is steadily improving agreement that energy over the southeastern mainland/northeastern Pacific as of Monday should consolidate into an upper low that retrogrades along the Aleutians around Wednesday-Thursday. Cold temperatures supported by strong surface high pressure tracking from the northern mainland into northwestern Canada should moderate slowly with time while a strong gradient south of the high will support brisk to strong winds over the southern mainland and Panhandle. Most precipitation next week will be confined to the Aleutians and Alaska Peninsula/Kodiak Island. ...Guidance Evaluation and Preferences... Today's guidance exhibited tendencies similar to recent days, with the operational models generally ahead of the ensemble means in depicting the strength of the upper ridge/high as the means continue to trend stronger in the direction of the models. At the same time the ECMWF/CMC and their means have tended to lead the GFS/GEFS with the ridge's strength/evolution/location, though sporadic GFS runs have been relatively close to the model consensus. Most guidance has gravitated to having the high center meander over the vicinity of eastern Siberia for most of the week, for a time achieving a 564dm contour before weakening somewhat late in the week. By the latter half of the week the 12Z GFS becomes a little slower than consensus with the Arctic ridge that rotates into the mainland. Meanwhile to the south there has been a noticeable trend in the models over the past day or so for deeper and faster retrogression of an upper low near the Aleutians by Wednesday-Thursday. In the 12Z cycle the ECMWF/UKMET/CMC ended up in very similar positions for the retrograding low through early Wednesday while the GFS was a little farther east. Details diverge thereafter. There is a decent signal in the models/means for a western Pacific system to come into the picture and track far enough east by late week for the northern side of the circulation to affect the Aleutians. As was the case the past couple days, various aspects of continuity and trends again favored an operational model blend through the entire period to maintain the best definition of the upper ridge and surrounding features as well as the surface features/gradients over the mainland and Panhandle. The divergence in the models for some of the less confident aspects of the forecast, in particular the details south of the upper ridge after midweek, provided some smoothing where appropriate. The forecast started with the 12Z ECMWF/GFS/CMC/UKMET from day 4 Monday into early day 6 Wednesday and then trended to half total ECMWF weight (split between the 12Z and 00Z runs) with the remainder tilted a little more to the 12Z CMC relative to the 12Z GFS. In most respects the new 18Z GFS provided some favorable trends toward the preferred solution. ...Weather/Hazard Highlights... Most of the mainland will see dry weather next week as strong high pressure over the northern mainland on Monday settles into northwestern Canada while a weaker surface ridge likely persists over the northern half of the mainland into late week. Far northern/northeastern locations could see a little light snow toward Thursday or Friday. Much below normal temperatures over the southeastern half or so of the mainland will slowly trend less extreme with time while readings should stay well below normal over the Panhandle the entire week. On the other hand the North Slope will see a pronounced warming trend with temperatures reaching well above normal by mid-late week. The western Aleutians will see enhanced precipitation/wind extend into at least Monday. Developing easterly flow at the surface and aloft should spread moisture from Kodiak Island and parts of the Alaska Peninsula through the Aleutians. Low-confidence surface low details will determine if there may be some localized enhancement of precipitation/wind. A separate system emerging from the western Pacific could increase moisture/wind over the Aleutians by late week. Rausch Hazards: - Heavy precipitation across portions of the Alaska Panhandle, Sun, Jan 2. - High winds across portions of the Alaska Panhandle and mainland Alaska, Sun-Mon, Jan 2-Jan 3. - High winds across portions of the Aleutians, Mon, Jan 3. - Much below normal temperatures across portions of the Alaska Panhandle and mainland Alaska, Sun-Thu, Jan 2-Jan 6. 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