Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 656 PM EST Tue Feb 25 2025 Valid 12Z Sat Mar 01 2025 - 12Z Wed Mar 05 2025 ...Overview... Latest models and ensembles still show varying degrees of upper ridging likely to extend from the Panhandle and western Canada into a decent portion of the mainland from the weekend into the middle of next week. North Pacific waves, and eventually an Aleutians system in the early to middle part of next week, should favor episodes of precipitation along the southern coast and to a lesser extent the Panhandle. Expect a majority of the state to see above to well above normal temperatures during the period, though the North Slope may still see some modestly below normal readings into Saturday before a warming trend. ...Guidance Evaluation and Preferences... While there is decent agreement for the large scale pattern overall, there is a lot more spread for embedded details. What clustering there has been among recent dynamical and machine learning (ML) guidance favored starting today's forecast with an emphasis on the 00Z/12Z ECMWF runs and the 12Z CMC during the weekend, followed by a transition toward phasing out the CMC and increasing 12Z CMCens/00Z ECens mean weight to 40-60 percent by early-mid week while maintaining some 00Z/12Z ECMWF input. Short-range strong low pressure south of the Alaska Peninsula during the latter half of this week should ultimately elongate/weaken and reach the southwestern mainland and southern Gulf of Alaska by early Saturday. Over the past couple days the GFS/GEFS mean have been straying deeper and westward versus nearly all other dynamical/ML guidance for the western mainland low while showing less Gulf low pressure than consensus. The new 18Z GFS is finally trending a lot closer to other guidance. Behind this area of low pressure, a relative majority of guidance has been suggesting that a wave will break off from an elongated area of North Pacific low pressure and generally track toward the Alaska Peninsula/Kodiak Island and the Kenai Peninsula during the weekend. This scenario is still far from unanimous and a fair amount of timing spread exists among solutions that show this wave. Latest GFS runs lean a bit fast while the 12Z CMC leans slow. The combination of these timing differences and perhaps details aloft cause GFS runs to show higher surface pressures than nearly all other guidance over much of the mainland around Monday. Most ML models indicate that what North Pacific low pressure remains behind this leading wave should consolidate to the south of the Alaska Peninsula by next Monday, with some divergence in details by Tuesday. At least the ML models show a general theme of the supporting upper trough achieving a decent negative tilt with potential for an embedded low to close off. ECMWF/CMC runs and their corresponding means are closest to this idea among dynamical guidance at the surface and aloft. GFS runs pull the main surface low back into the Bering Sea--within the broad spread from the past couple days but a scenario that is becoming more in the minority among the ML models. This is part of a general evolution toward more north-south orientation of deep-layer flow in the 12Z GFS late in the period, leading to greater precipitation than consensus over the Alaska Peninsula and far western mainland. Meanwhile the 06Z through 18Z GFS runs are suppressed versus consensus for low pressure emerging from the northwestern Pacific and most likely tracking along the Aleutians around Tuesday-Wednesday. The GEFS mean shows some of the suppressed theme with leading low pressure but eventually joins the other means by next Wednesday. Especially by Wednesday the dynamical/ML guidance becomes fairly random with respect to which individual low within the broader east-west axis of lower pressures will be dominant. Also of note, the ML average suggests this general axis could reach a bit north of the Aleutians. A model/ensemble mean approach offers a reasonable starting point to balance definition versus high uncertainty in specifics. Farther north, guidance seems to be trending better defined with an upper low/trough drifting northward across the Bering Sea and Siberia, with some height falls possibly extending into the far western mainland. The ML models suggest the ECMWF could be somewhat overdone with the western mainland height falls though, favoring the ensemble mean inclusion by mid-late period. This overall trend leads to a better defined wavy frontal boundary pushing across the western mainland behind a leading warm front. Pattern evolution later in the period should ultimately lead to a southwest-northeast oriented stationary front. ...Weather/Hazards Highlights... What is left of late week Northeast Pacific low pressure should produce moderate coastal rain and higher elevation snow along and near the southern coast on Saturday, with some light precipitation also possible over the southwestern mainland. A potential trailing wave with still uncertain details may bring somewhat more focused precipitation to the Kenai Peninsula and eastward along the Southcentral coast. At this time precipitation totals are not expected to reach hazardous criteria in general, but some localized enhancement is possible. Both features may bring some moisture to the Panhandle (more over northern parts), while some light snow may spread northward across the western mainland near a wavy front. Another system that may evolve/track south of the Alaska Peninsula early next week would continue to support periods of precipitation. The system forecast to track from the northwestern Pacific into the Aleutians early-mid week should become the dominant feature by Wednesday, eventually increasing winds across a broad area over the Pacific and Bering Sea plus spreading organized precipitation across the Aleutians and then supporting an easterly flow of moisture into the Alaska Peninsula. Depending on system details and timing on Wednesday, some precipitation may reach farther eastward/northeastward. Expect temperatures to be above normal over a majority of the state through the period along with a gradual warming trend from this weekend into early next week. There should be decent coverage of plus 10-20F or greater anomalies. The North Slope will be an exception, as Arctic high pressure supports somewhat below normal readings that may linger into Saturday before the general warming trend pushes anomalies above normal. Meanwhile a wavy front pushing across the western mainland may lead to some cooling over western areas from the weekend into early next week but temperatures should remain above normal. 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