Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 659 PM EST Thu Jan 25 2024 Valid 12Z Mon Jan 29 2024 - 12Z Fri Feb 02 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 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 and into the early part of next week. Much below normal temperatures over most of the Interior and Southwest look to persist into next week with the upper trough overhead, but should trend milder by early next week in the eastern Interior as upper ridging attempts to build back in to the region. ...Guidance Evaluation/Preferences... On the large scale, models and ensembles show good agreement with a stubborn upper trough slow to move over Mainland Alaska much of next week as strong blocky ridging holds over western/northwest Canada. There is some disagreement still on the centroid of the embedded upper low, especially as the week goes on, though even as early as Day 4/Monday, the CMC is displaced well to the north (in the Arctic) of the rest of the guidance (North Slope area). By mid to late next week, the ECMWF tends to drag the main upper low west across far eastern Siberia as another piece of energy lifts north across the Mainland, while the GFS meanders near the North Slope before slowly shearing and lifting north. The ensemble means show better support towards the GFS in this evolution than the ECMWF. 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. But there is considerable spread in exact placement of these lows which has implications for weather across the Southern Coast/Panhandle. The most notable difference is the 12z GFS is displaced well to the northwest of the guidance with one strong system lifting into the Gulf next Wednesday. Otherwise, late period, lots of noise and placement variability in the next system approaching the western Aleutians, but good agreement in the ensemble means. The WPC forecast for today used a general blend of the deterministic guidance (skewed more towards the ECMWF) for days 4-5 before quickly incorporating the ensemble means days 6 and beyond amidst growing forecast spread in individual systems which have low predictability at these longer time scales anyways. On the large scale though, this approach did maintain relatively good continuity with yesterdays WPC forecast too. ...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, 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, gap winds that could be quite gusty are likely into early next week for the Alaska Peninsula and Kodiak Island to Cook Inlet, with some lingering Gusty winds Sunday into Monday across the southern coast of the Alaska Peninsula. Bitterly cold temperatures that are well below normal are forecast for the Interior into next week. Overnight lows lower than -30F will be widespread, with some -50s possible in favored valleys of the Yukon Flats and Interior mainly early week. 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. Santorelli/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