Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 744 PM EDT Wed Apr 03 2024 Valid 12Z Sun Apr 07 2024 - 12Z Thu Apr 11 2024 ...Upper lows in the Gulf of Alaska will promote precipitation for Southcentral to Southeast Alaska and periods of gap winds behind... ...Overview... Over the weekend into early next week, an upper trough/low will push across the Bering Sea and Alaska Peninsula into the Gulf of Alaska, along with a surface low. The surface low should be weakening but could produce high winds to possibly storm force for the Aleutians on Saturday. Then it is becoming more likely that Arctic energy will spill southward and serve to restrengthen the upper low in the Gulf around Tuesday-Wednesday, cooling temperatures. This pattern will lead to prolonged moist onshore flow promoting precipitation from the southern coast into Southeast Alaska through much of next week. West of the low, northwest flow could cause some gap winds from the Alaska Peninsula to Kodiak Island and the Kenai Peninsula, peaking around Monday. By Wednesday-Thursday, another upper low is forecast to come into the Bering Sea. ...Guidance Evaluation and Preferences... Model guidance remains in reasonably good agreement for the early part of the period, indicating lobes of vorticity near the eastern Aleutians/Alaska Peninsula and in the Gulf of Alaska on Sunday before the western one takes over and stays over the Gulf Monday-Tuesday. There are some slight timing/placement differences, including GFS runs showing a surface low just south of the Alaska Peninsula early Sunday whereas non-NCEP guidance is to the north, but minor enough that a multi-model deterministic blend worked well for the early part of the period. Models have persistently shown troughing across the Mainland to Gulf into much of next week, with some detail differences. Recent guidance has now started to be more agreeable with showing possibly potent energy spilling south from the Arctic into the Mainland late Monday into Tuesday, that then recreates/reinforces an upper low in the Gulf by midweek. The CMC/ECMWF had been showing this a day ago, and now the 06Z/12Z GFS runs have joined them, though with some variations. The 12Z GFS in particular split the energy diving south, with some lingering in the northwestern Mainland into Thursday. The 06Z GFS run seemed to be in better alignment with the other guidance. Models then show another upper/surface low coming east Wednesday-Thursday through the Bering Sea. There is some spread in the position and strength but certainly within typical spread for the Day 7-8 period. The CMC keeps more of an open trough while other models show a closed low. Thus the WPC forecast transitioned from a blend of the deterministic guidance including the 06Z and 12Z GFS and 12Z ECMWF/CMC/UKMET to gradually favor more ensemble means later in the week, reaching half the blend by Day 8. Reduced the proportion of the 12Z GFS and CMC in particular for the latter half of the period. ...Weather/Hazards Highlights... The surface low in the Bering Sea will be rather deep into Saturday, and winds possibly reaching storm force are possible across the Aleutians south of the low track. Light to moderate precipitation is likely across the Aleutians to Alaska Peninsula as well. The low weakening as it passes across the Alaska Peninsula and into the Gulf should cause winds to lessen, but may still be brisk in those areas. Initial and reforming upper and surface lows set up over the Gulf will promote moist Pacific inflow for precipitation across the southern coast of the Mainland to Southeast Alaska. While amounts are not forecast to be terribly heavy on any particular day, totals will add up with multiple days of moderate amounts through next week. Additionally, a front or two coming through northern Alaska could help generate areas of light snow farther north across the Mainland. On the backside of the Gulf lows, northwesterly gap winds could be somewhat strong for the Alaska Peninsula to Kodiak Island and to the western Kenai Peninsula and surrounding waters, likely peaking in strength on Monday. High temperatures within a few degrees of average are expected on Sunday across the Mainland, with generally above average lows. But into Monday-Tuesday, especially with increasing potential for Arctic energy to dig, a cooling trend is likely for much of the Mainland. The largest anomalies of 15-25 degrees below normal are forecast over west-central and southwestern parts of the Mainland into the Alaska Peninsula, equating to below 0F temperatures possible south as far as the Lower Yukon. Gradual moderation closer to normal is forecast for midweek and beyond, possibly reaching above average for the North Slope. Southeast Alaska should see near average lows but persistent below normal highs next week given the precipitation chances. 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