Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 654 PM EST Wed Feb 07 2024 Valid 12Z Sun Feb 11 2024 - 12Z Thu Feb 15 2024 ...Overview... Guidance continues to show a steadily building upper ridge over the far northeastern Pacific/Alaska Panhandle/western Canada into Mainland Alaska over the course of next week, though with continued uncertainty for the shape of the ridge by around the middle of next week. Coinciding with the initial strengthening of the ridge, a number of operational models suggest that North Pacific/Aleutians upper dynamics should support a strong northward-tracking North Pacific into Bering Sea storm during the first half of the week. This system and the overall pattern evolution would shift wind and precipitation focus to an area centered on the Alaska Peninsula. Over this region low level winds should turn more easterly by midweek as the upper ridge suppresses upper troughing and surface low pressure over the north-central Pacific. Expect well above normal temperatures over the west and north, while surface high pressure becoming established over northwestern Canada should support below normal readings over the Panhandle and parts of the eastern Interior. ...Guidance Evaluation/Preferences... To a somewhat more noticeable degree than yesterday, the GEFS/ECens means have been showing a gradually stronger trend for the upper ridge building over northwestern North America. This provides support for operational model emphasis at least for the first half of the period. Meanwhile, consecutive GFS/ECMWF/CMC/ICON model runs have been depicting fairly strong development of North Pacific/Aleutians low pressure by Monday, weakening some as it tracks into the northern Bering Sea and Siberia. With some lingering spread for surface low timing and track, the favored blend used a split of 00Z/12Z ECMWF runs along with the 12Z GFS and minority input from the faster 12Z CMC during days 4-6 Sunday-Tuesday. Minor manual enhancements to the blend brought the central pressure of the low down a bit to around 970 mb over the Aleutians as of early Monday. This is in the middle to slightly weaker side of the model spread, though the new 18Z GFS has trended a little weaker. In spite of the relative majority clustering for this storm, confidence in some specifics is still not great. The past couple UKMET runs have been slower to build the upper ridge and more diffuse with what low pressure there is over the North Pacific, leading to a longer period of southern coast/Panhandle precipitation focus. Ensemble means show surface development reaching the Aleutians on Monday, supporting the operational runs in principle, but continue their reluctance to track the system as far northward over the Bering Sea as indicated by the operational GFS/ECMWF cluster. Also contributing to lower than desired confidence, latest runs of the ECMWF-initialized machine learning models vary considerably for the strength of surface low pressure and track (most not as deep as the operational models and a couple taking a farther east track than consensus). By midweek guidance essentially diverges into two clusters. Latest GFS/ECMWF/CMC runs now provide a strong signal toward an upper high closing off over southeastern Alaska/northwestern Canada (GFS more over the mainland and the ECMWF/CMC farther east), which had been only a minority scenario 24-36 hours ago. However the ensemble means and machine learning models still favor maintaining a more open upper ridge through the period--though the new 12Z ECens mean (arriving after forecast preparation) is starting to hint toward an implied closed high over or just north of the Panhandle. Preference is to transition the early-mid period operational model blend toward a model/mean compromise, which ultimately closes off an upper high but in less pronounced fashion than the models. The upper high position is much closer to the ECMWF/CMC versus the GFS. For the most part, either scenario has the dominant area of low pressure settling over the north-central Pacific by late in the period. Upper ridge specifics will determine how much northwestern Canada surface high pressure extends into the mainland and direction of isobaric gradient from the mainland through the Bering Sea/Aleutians/North Pacific, with the forecast blend compromising within this potential range. ...Weather/Hazards Highlights... Forecast deepening of North Pacific low pressure as it progresses into the Aleutians around Monday and a continued northward track thereafter would produce an early-week episode of strong southeasterly winds and heavy precipitation across portions of the eastern Aleutians and the Alaska Peninsula. Some of the wind and precipitation effects may extend farther north over the western mainland. Confidence in specifics is currently not sufficiently high to depict in the Days 3-7 Hazards Chart but this system merits close monitoring. A trailing front may aid persistence of rain/snow focus through at least Tuesday. Increasing dominance of mid-latitude Pacific low pressure should turn winds more easterly over the Alaska Peninsula by midweek, maintaining some precipitation enhancement but likely with somewhat lighter totals. Locations from Prince William Sound through the Panhandle may see mostly light precipitation continue into Sunday but will likely trend drier as upper ridging builds. Expect the pattern evolution to favor above normal temperatures over a majority of the state with the highest anomalies over western and northern areas. High pressure becoming established over northwestern Canada should promote colder/below normal readings over the Panhandle along with some pockets of near to somewhat below normal readings over the eastern mainland. 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