Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 758 PM EDT Thu Mar 20 2025 Valid 12Z Mon 24 Mar 2025 - 12Z Fri 28 Mar 2025 ...Overview... Early next week, a mean upper trough over western Alaska and a mean ridge in the east will allow for a slow-moving surface low to set up in the northern Gulf. Onshore flow ahead of this low will keep coastal showers and mountain snow ongoing during this time for the southern coast. Colder than average temperatures are forecast behind the low, along with moderate gap winds focused in the Alaska Peninsula. As next week progresses, troughing/energy should feed into the northern Pacific, where a large upper and surface low may drift northward and impact at least Southeast Alaska with precipitation chances by later next week. ...Guidance/Predictability Assessment... Model guidance shows reasonably good agreement on the large scale pattern with a mean trough axis extending across Alaska southward into the northern Pacific next week. But there are plenty of differences in the smaller features within the broader scale. At the start of the period Monday, the surface low in the Gulf has a position farther south in the GFS runs than in the ECMWF/CMC/UKMET better consensus. Then there are a couple of shortwaves tracking east that show model spread as well. First, a small upper low over Kamchatka Monday is forecast to track through the Bering Sea as a shortwave. Recent GFS and ECMWF runs as well as the AIFS have similar timing of this feature through Wednesday, and indicate it weakening. However, the UKMET and CMC are considerably slower and maintain the feature longer, leading to out of phase differences in the Bering Sea. The ensemble means do not really show this shortwave much at all, likely an indicator of the spread. Tended to favor a weakening and progressive solution close to the GFS/ECMWF. But, then the ECMWF is the most aggressive with another shortwave coming in over the Bering Strait or so by Thursday, which was not preferred at this point. In the Pacific, models indicate an upper low closing off around midweek that pivots east and then northward approaching Alaska. The CMC seems to be an outlier in showing a farther southeast position with the upper low and associated surface low into later week. Then by Friday the 12Z GFS has a shortwave rounding the western and southern side of the upper low that disrupts it, and its surface low central pressure becomes weaker. The ECMWF (though on the stronger side with the central pressure) and the ensemble means seemed to have the best consensus. Thus, the WPC forecast used a mostly deterministic blend favoring the ECMWF and GFS early in the period, but quickly increased the proportion of GEFS and EC ensemble means as the period progressed given the increasing spread. ...Weather/Hazards Highlights... The southern coast and Panhandle will likely see periods of mainly light to moderate coastal rain and mountain snow on Monday and lessening Tuesday in association with gradually weakening low pressure settling over the northeastern Pacific/southern Gulf of Alaska. Flow behind the Pacific low pressure system may produce periods of brisk northerly gap winds over the Aleutians and into the Alaska Peninsula Monday, but remaining below hazardous thresholds. Portions of the western mainland may see scattered light snow continuing into Monday along a persistent wavy surface front that should slowly push eastward. A weakening front could provide precipitation to the Aleutians Monday-Tuesday. Much of Alaska should be dry for midweek. But by later next week, large upper/surface lows moving northward through the Pacific will likely allow for precipitation in Southeast Alaska, though the details are yet to be determined. The narrow upper trough extending southeast from eastern Siberia will keep temperatures well below normal over the Alaska Peninsula and western portions of the Mainland on Monday. Expect temperatures to gradually moderate closer to normal by Tuesday- Wednesday as the upper trough weakens. The North Slope and Brooks Range may be slightly above average through much of next week, while the Interior and the Panhandle could see a mix of above and below normal temperatures. Tate/Hamrick 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