Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 655 PM EST Tue Feb 13 2024 Valid 12Z Sat Feb 17 2024 - 12Z Wed Feb 21 2024 ...Overview... The best clustering of guidance shows a deep storm near the western Aleutians as of early Saturday drifting into the central Bering Sea and weakening by next week, while shortwave energy flowing around the southern/eastern side of the associated upper low gradually erodes the upper ridge extending from western Canada northwestward through Mainland Alaska into the weekend. Depending on shortwave details, some degree of ridging could persist or rebuild over and near western Canada by the middle of next week. A combination of the leading surface front anchored by the initial Aleutians-Bering Sea storm and then one or more trailing waves/fronts should lead to episodes of precipitation along and near the southern coast eastward into the Panhandle. Another vigorous storm system could track near the Aleutians around next Tuesday-Wednesday. ...Guidance Evaluation and Preferences... Latest guidance is consolidating toward a rather strong depiction of low pressure forecast to be near the western Aleutians at the start of the period early Saturday, with operational model runs nearly unanimous in showing a central pressure a little above or below 960 mb. 00Z ECMWF-initialized machine learning models offered support for similar depth, adding confidence in refining continuity toward the deeper solution. After Saturday the guidance shows typical divergence, with recent GFS runs straying a bit to the east/northeast (but with the 12Z run less pronounced than the 06Z version) and the UKMET tracking farthest south. CMC runs have been a tad on the slow side. GEFS/ECens means have favored an intermediate track, leading to an ultimate preference among the 00Z/12Z ECMWF runs and 12Z GFS (slightly tilted to the ECMWF run) to depict the desired detail and track for this storm. The new 18Z GFS has adjusted back to at least far west as the preferred solution. Farther east, operational models have been rather inconsistent over how leading energy will push into the downstream ridge. The overall consensus of operational models, machine learning models, and ensemble means would support some shortwave energy reaching at least into the southwestern mainland by early next week--albeit with a lot of spread for what shape this energy will take after that time. This at least favors leaning away from the much stronger ridge seen in the 12Z CMC that shows a much slower frontal/moisture progression along the southern coast. The majority scenario would have the deep Aleutians/Bering Sea storm's leading front weakening as it reaches the southwestern mainland by early Sunday, with a potential succession of waves/fronts reaching the southern coast next Monday-Wednesday as suggested by latest GFS/ECMWF runs. This fits within the overall pattern of the ensemble means but the means do not yet depict any well-defined waves due to the waves' medium to small scale and ensemble member spread. Blend preferences reflect the potential of these waves in weaker form of the GFS/ECMWF runs but with minimal confidence in specifics. Returning to the Aleutians mid-late period, there is a reasonable signal for a compact system to track a little south of the Aleutians early in the week followed by a somewhat larger-scale and stronger storm tracking through the Aleutians/southern Bering Sea Tuesday-Wednesday. A model/mean mix provides a good starting point for the latter storm, with a deeper trend in the 18Z GFS (closer to 00Z/12Z ECMWF runs) and east/southeast adjustment for track in the 12Z ECens providing additional confirmation of the favored blend in principle. The first half of the forecast period (Saturday through early Monday) started with a blend of 60 percent total 12Z/00Z ECMWF and 40 percent 12Z GFS to reflect preferences for the deep Aleutians/Bering Sea storm as well as the pattern to the east. This model composite rapidly transitioned to 40-60 percent total input of the 12Z GEFS/00Z ECens means by days 7-8 Tuesday-Wednesday to account for model detail uncertainties but some common themes within a more agreeable larger scale pattern. ...Weather/Hazards Highlights... From Friday (before the start of this discussion's forecast period but covered in the Days 3-7 Hazards Chart) into Saturday there will be two areas of focus for impactful weather. The eastern/central Alaska Peninsula and Kodiak Island will see a threat of heavy precipitation that should be enhanced by strong easterly low level winds, while the central/western Aleutians should experience high winds on the leading side of deep low pressure forecast to reach the western Aleutians by early Saturday. A weakening front extending from this storm may focus some precipitation over the Alaska Peninsula and vicinity during the weekend as well. From Monday onward expect the best moisture focus to extend between the southern coast and Panhandle with one or more waves/fronts whose exact details are very uncertain at this time. There is currently some signal for relatively higher totals from near Prince William Sound into the far northern Panhandle during Monday-Tuesday. Any waves on the stronger side of the guidance spread would also enhance winds. Precipitation extending farther north across the mainland should be lighter and favor western areas. Another storm system tracking into Aleutians/southern Bering Sea by next Tuesday-Wednesday may bring strong winds and organized light to moderate precipitation. Initial upper ridging, and then continued Pacific influence even with some erosion of the ridge, will favor above normal temperatures across most of the state. Expect the greatest anomalies to be in the western to northern parts of the mainland and possibly reaching at least 30 degrees milder than normal into the weekend. Some cooling will be possible next week but still with above normal anomalies. Some pockets of near to slightly below normal temperatures will be possible over the eastern Interior and mostly for daytime highs over portions of the Panhandle. 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