Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 701 PM EST Fri Jan 24 2025 Valid 12Z Tue Jan 28 2025 - 12Z Sat Feb 01 2025 ...Colder trend to well below normal temperatures next week with enhanced gap winds possible next Thursday... ...Overview with Guidance Evaluation and Preferences... As the medium-range period begins next Tuesday, guidance continues to show better agreement on the departure of a significant low pressure system off to the east and northeast of mainland Alaska, followed by an abrupt change to a cold regime for the remainder of next week. A trailing piece of 500mb trough in the wake of the departing low is forecast to dig southeast across the Alaska Peninsula by next Tuesday into Wednesday. Deterministic solutions as well as ensemble means show reasonably good agreement on this feature till Tuesday before they begin to diverge on Wednesday in terms of how much this trough will further amplify downstream over the Gulf of Alaska for the latter half of next week. The 12Z Canadian model (CMC) appears overly aggressive in this regard as it spins up a cyclone that is much deeper and much farther west than its ensemble mean just off the Alaska Peninsula. This solution is not supported by both the GFS and ECMWF as well as their ensemble means. Despite the divergence of the deterministic solutions noted above, ensemble means from the GEFS, ECMWF, and CMC are converging toward a gradually weakening cyclone centered over/near the Gulf of Alaska for the latter part of next week. Guidance in general is showing a period of enhanced precipitation heading onshore in the vicinity of the Panhandle midweek with some spread on the north-south extent of the heavy precipitation. The enhanced precipitation is generally forecast to slide southward down the Panhandle through late next week. Meanwhile, guidance is showing good agreement for an arctic high pressure system to build east into the northern half of Alaska. Over the Aleutians, guidance is indicating general agreement for a large-scale cyclone to edge into the island chain from the west from midweek onward, with significant divergence of the deterministic solutions on Days 7 and 8. Ensemble means are in relatively good agreement though. The WPC medium-range forecasts were derived based on a consensus of the 12Z ECMWF and 00Z/12Z EC mean, the 12Z GFS/GEFS, and the CMC mean. The CMC deterministic solutions were kept only for the beginning of the forecast period. This blend yielded a solution very compatible with WPC continuity. ...Weather/Hazards Highlights... As the cyclone departs mainland Alaska next Tuesday, the remaining snow across interior Alaska and heavy precipitation across the Panhandle will be in the process of tapering off. Thereafter, expect most areas to the north of the southern coast to trend drier. After a brief lull, some moisture may return to the southern coast/Panhandle for the latter half of the week, depending on upper trough/surface low details. Best potential for additional precipitation will be from the Panhandle to the Southcentral coast. A Bering Sea wave may bring a period of mostly light precipitation to the eastern Aleutians/Alaska Peninsula on Tuesday. Northerly/northwesterly winds over the eastern Aleutians/Alaska Peninsula should strengthen behind this wave and its cold front, and the tightening surface gradient between low pressure over the Gulf of Alaska and surface ridge over the northern mainland will also raise the potential for strengthening gap winds farther east along the southern coast midweek. Thursday appears to be the day when the gap winds will be the strongest as high pressure begins to build in from the north while the Gulf of Alaska cyclone remains relatively strong. The temperature forecast remains on track, with the early part of the week featuring a west-to-east transition from above normal to below normal readings. Well below normal temperatures (by at least 20F over some areas) should cover much of the western-central mainland by Wednesday, with perhaps some lingering pockets of slightly above normal still over the North Slope and southern Panhandle. Coldest anomalies should continue to nudge eastward a bit during Thursday-Friday. While there are continued uncertainties with the surface pattern over and near the Gulf by mid-late week, ensemble guidance offers a very strong signal for this episode of cold weather across much of the mainland. Kong/Rausch 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