Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 632 PM EST Wed Jan 24 2024 Valid 12Z Sun Jan 28 2024 - 12Z Thu Feb 01 2024 ...Upper trough pattern will lead to a multi-day heavy precipitation threat for Southeast, high winds for the Aleutians/Alaska Peninsula, and hazardous cold for parts of the Interior... ...Overview... An upper trough is forecast to dominate the pattern over Mainland Alaska this weekend into much of next week. This upper trough should help to pull a series of surface systems northward into the Northeast Pacific/Gulf of Alaska over the course of the period, bringing multiple days of significant precipitation to the Panhandle and parts of the southern coast. Meanwhile a tight surface pressure gradient across the Aleutians and southern tier, enhanced at times by individual storm systems, should produce brisk to strong winds this weekend into early next week. Much below normal temperatures over most of the Interior and Southwest through Saturday look to persist in the Southwest into next week with the upper trough overhead, but should trend milder by early next week in the eastern Interior. ...Guidance Evaluation/Preferences... Models have been persistent in indicating upper troughing meandering atop the western mainland through the first half of next week. The centroid of an embedded upper low within the trough is more questionable, however. Model guidance from a day ago showed pretty good consensus on the upper low atop the state, around the Seward Peninsula or so. However, 00Z/06Z GFS runs started a trend of indicating the upper low farther north into the Chukchi Sea, which the 12Z ECMWF and CMC then supported as well. While troughing remains across the western part of the mainland regardless, the placement of the core of the low may make have impacts on the magnitude of cold temperatures, for example. Details of energy possibly splitting into Southcentral Alaska or nearby, as indicated by the 12Z GFS on Tuesday and the 12Z CMC on Wednesday, are also questionable. Overall guidance seems to indicate a trend toward a more negatively tilted trough by midweek, with average confidence. At the surface, model guidance is persistent with indicating surface lows tracking east through the northern Pacific and then pivoting north into the Gulf of Alaska or northeast Pacific, with expected levels of spread in the low positions and strength. There also may be some weak surface waves moving through the Bering and perhaps across the Aleutians on the backside of the trough. Given the somewhat agreeable large scale pattern with differences in the details, a model blend of the 12Z deterministic guidance worked well for the start of the period, and then trended toward favoring the ensemble means by more than half by the late period. This allowed for a trend toward the model consensus of an upper low farther north, but not as dramatic as some of the individual models. Ensemble means, especially the EC mean (even the 12Z EC mean that was not available at forecast time) show the center of the upper low farther south than some of the deterministic models, so incorporating those gave a nod to continuity for a less dramatic change, which was fortunate especially considering the uncertainty. ...Weather/Hazards Highlights... From this weekend into early next week, Southeast Alaska will see periods of heavy rain and snow (depending on location/elevation) as a possibly moderate to strong atmospheric river affects the region. This moisture shield also is forecast to extend westward along the southern coast into Prince William Sound and perhaps as far west as the eastern Kenai Peninsula over the weekend, as multiple surface systems likely track northward into the Gulf of Alaska. Over areas that are sufficiently warm, effects of the potentially heavy rain on top of current snow cover will also have to be monitored. Lesser amounts of moisture streaming northward may produce some snow over at least the eastern mainland. Meanwhile, a tight surface gradient across the southern tier and fronts moving through may yield periods of strong winds for the Aleutians lingering into Saturday. Farther east, gap winds that could be quite gusty are likely this weekend into early next week for the Alaska Peninsula and Kodiak Island to Cook Inlet. Bitterly cold temperatures that are well below normal are forecast for the Interior into Saturday. Overnight lows lower than -30F will be widespread, with some -50s possible in favored valleys of the Yukon Flats and Interior. Eastern portions of the Interior should gradually moderate and become milder early next week as the trough aloft pivots. However, southwestern parts of the mainland are expected to remain well below normal, with some slight and slow moderation to less extreme values by early-mid next week. Temperatures could cool again in the eastern Interior for midweek and beyond if the trough axis pushes east. Meanwhile, Southeast Alaska should see above normal temperatures especially through the weekend, gradually moderating closer to normal for highs (though remaining above normal for lows) as next week progresses. The North Slope looks to be around average for lows while highs could be below average into the weekend. Tate 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