Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 658 PM EST Tue Jan 23 2024 Valid 12Z Sat Jan 27 2024 - 12Z Wed Jan 31 2024 ...Upper low 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 low will track into north-central Alaska late this week and then likely settle over the western mainland by 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 at times. Much below normal temperatures over most of the Interior and Southwest late this week look to persist in the Southwest into next week with the upper low overhead, but should trend milder by early next week in the eastern Interior. ...Guidance Evaluation/Preferences... Models continue to display better than average confidence on the large scale pattern, with the main feature the upper low that will migrate into the state by the weekend and meander over the western mainland. Individual shortwaves within the trough/low and its exact centroid may be more questionable but certainly within reason for the medium range period. Over the weekend, some minor spread remains with the upper low position, with the UKMET and the CMC ensemble mean on the southwestern side of the spread with the center of the low. Instead preferred a blend of the deterministic ECMWF/GFS/CMC early in the period, which showed a more agreeable solution that is similar to yesterday's forecast position as well. Today's models also continue to indicate that the trough should take on a negative tilt during early-mid next week. 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. Most models seemed within reason through the weekend, so the above blend worked well at the surface. But increasing spread in these lows and details aloft led to including the GEFS and EC ensemble means in the blend and upping their percentage to half on Day 7 and a bit more on Day 8 to reduce individual model details that were more variable. There also may be some weak surface waves moving through the Bering and perhaps across the Aleutians on the backside of the trough. ...Weather/Hazards Highlights... From late this week into early next week, Southeast Alaska should see periods of heavy rain and snow (depending on location/elevation) as a likely moderate to strong atmospheric river affects the region. Into the weekend, this moisture shield also extends westward along the southern coast into Prince William Sound and perhaps as far west as the eastern Kenai Peninsula, 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 late this week. Farther east, gap winds that could be quite gusty are likely this weekend into early next week into the Alaska Peninsula and Kodiak Island to Cook Inlet. Bitterly cold temperatures that are well below normal are forecast for the Interior late this week. Overnight lows lower than -30F will be widespread, with some -50s possible in favored valleys of the Yukon Flats. 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 just perhaps some slight moderation to less extreme values by early-mid next week. 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. 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