Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 756 PM EDT Tue Mar 18 2025 Valid 12Z Sat 22 Mar 2025 - 12Z Wed 26 Mar 2025 ...Overview... Continuity has held up quite well for the overall forecast during the period. From the weekend into early Monday, expect one or more surface waves to reach into the northeastern Pacific/southern Gulf of Alaska from an initial elongated North Pacific system but with gradual weakening. The waves should produce unsettled weather along the southern coast in the form of mostly light to moderate precipitation while the gradient farther west will produce breezy conditions from the Aleutians into the Alaska Peninsula. Guidance still shows a ridge building from the Pacific through Aleutians/Bering Sea by Sunday- Monday with a corresponding digging of east-central Pacific troughing. A part of the Bering Sea ridge could reach the mainland around Tuesday-Wednesday while a leading trough should steadily fill as it pushes in from the western coast by Monday. The amplifying trough to the south should pull Pacific low pressure emphasis southward toward midweek, leading to a drier trend along the southern coast. Some moisture may still reach the southern Panhandle though. Arctic high pressure will likely maintain brisk easterly winds across the North Slope into the start of next week, with some uncertainty in the exact pattern thereafter. Below normal temperature anomalies over the far west on Saturday should expand eastward some before moderating as the upper trough fills. Most other areas should see near to above normal temperatures. ...Model guidance and predictability assessment... Guidance agrees quite well for the overall pattern/system evolution during the weekend, with the primary system of interest being a general area of low pressure tracking northeastward from south of the Alaska Peninsula. The wave is initially a frontal wave ahead of parent low pressure that stays over the mid-latitude Pacific. Models continue to show smaller scale detail differences that have very low predictability several days out in time, favoring a model blend approach to represent the overall feature while downplaying the less confident fine details. Farther north, the forecast has good continuity for an upper trough extending southeast from an eastern Siberia upper low with a wavy western mainland surface front on the eastern periphery of the trough. As upper ridging builds into the Aleutians/Bering Sea and a narrowing but weakening trough axis pushes into the western mainland by Monday-Tuesday, machine learning (ML) models have been offering best support for the ensemble means in principle the past couple days, with ECMWF runs tending to be the closest operational guidance to that idea. GFS runs have tended to hold the upper ridge farther west but have been trending some toward the means/ML models. The 12Z CMC finally looks closer to the majority cluster after lagging trends previously. Then toward the middle of next week the dynamical and ML models diverge for details of how shortwave energy may pass into or around the ridge, along with corresponding frontal and moisture details. ECMWF/CMC runs have been bringing more shortwave energy into the ridge with a farther east extent of fronts/moisture, while latest ensemble means and most ML models suggest at least tempering that scenario. By the latter half of the period there is not yet a well defined consensus for the exact depiction of high pressure to the north and east of the North Slope. ECMWF/ECens runs keep Arctic high pressure located more to the north of the mainland while other guidance shows varying degrees of southeastward displacement. Leaning toward an ensemble mean average looks reasonable at this time. Guidance comparisons during the latter half of the period favored a transition toward increasing ensemble mean weight (12Z GEFS/CMCens and 00Z ECens) with lingering 12Z ECMWF input. Ensemble weight reached 80 percent by Day 8 Wednesday. ...Sensible weather and potential hazards... The southern coast and Panhandle will likely see periods of precipitation from the weekend into Monday in association with gradually weakening low pressure settling over the northeastern Pacific/southern Gulf of Alaska. Most amounts should be on the light to moderate side. Individual waves could briefly enhance winds a bit along the coast and over open waters. Anticipate a drier trend after Monday as Pacific low pressure emphasis drops southward, though moisture on the northeastern periphery of that evolving system could extend into the southern Panhandle around midweek. Flow behind the Pacific low pressure systems may produce periods of brisk to strong northerly winds over the Aleutians and into the Alaska Peninsula, most likely during Saturday-Monday. Wind speeds should not reach hazardous thresholds though. Portions of the western mainland may see scattered light snow continuing into the weekend along a persistent wavy surface front that should begin to push eastward around Sunday. Flow around high latitude Arctic high pressure should maintain brisk easterly winds across the North Slope through the weekend and possibly into early next week. Winds may then trend lighter depending on uncertain details of this high. Returning to the Aleutians, guidance still shows a surface ridge bringing more tranquil conditions from west to east from Sunday into Monday or Tuesday. Southerly winds should strengthen over the western Aleutians early next week ahead of a frontal system anchored by low pressure forecast to track near Kamchatka. Current forecast preference has the fronts dying upon approaching the western mainland by next Wednesday with only a little scattered light snow if any moisture reaches the western coast. The upper trough extending southeast from an eastern Siberia upper low this weekend will keep temperatures somewhat below normal over far western areas. The below normal anomalies should expand eastward somewhat late weekend into Monday as the upper trough axis moves eastward. However the upper trough will be weakening with time, so temperatures should moderate toward or above normal by Tuesday-Wednesday. Most other parts of the mainland will likely see above normal readings most of the time, generally with warmer anomalies for morning lows relative to those for daytime highs. The Panhandle should maintain a more narrow than usual temperature range with above normal morning lows and near to below normal highs. 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