Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 759 PM EDT Tue Apr 02 2024 Valid 12Z Sat Apr 06 2024 - 12Z Wed Apr 10 2024 ...Overview... Troughing across the Mainland as the period begins over the weekend will be supplemented by an upper low pushing across the Bering Sea into the Alaska Peninsula, along with a deep but weakening surface low. Then the pattern decelerates into next week as this energy stays atop the Gulf of Alaska and the southerly flow ahead of it provides some prolonged precipitation chances to the southern coast into Southeast Alaska. Brief upper ridging is possible for the Aleutians and Bering Sea before additional energy may come in mid-next week. Farther north, there are some model differences with upper flow details over the Arctic and into the mainland into next week, with the most likely scenario being an Arctic upper low helping to anchor a deepening trough that extends south over the northwestern mainland. ...Guidance Evaluation and Preferences... Model guidance is in reasonably good agreement with initial troughing in the Mainland to Gulf over the weekend, and with the upper low over the Bering Sea and then across the Alaska Peninsula and into/near the Gulf, along with the accompanying surface low. The latter system nudged a bit slower than the previous forecast. A multi-model deterministic blend with minor incorporation of the GEFS and EC ensemble means worked well through the weekend. Trough energy and weakening surface low pressure then sits over the Gulf of Alaska into next week. The more uncertain part of the forecast is with Arctic energy possibly spinning down into the Mainland. The ECMWF and CMC produce a tongue of strong vorticity that goes southward through the western Mainland and enhances the troughing there. GFS runs are more variable but do not show energy diving this far south, while ensemble means do not either, though of course are subject to blending of their members. But it seemed safest not to have a feature this strong coming that far south. There are also some differences upstream. Upper ridging shows somewhat reasonable agreement across the Bering/Aleutians early in the workweek, though the CMC was out of phase with this and then some additional energy coming in by midweek. Thus through the latter part of the period, eliminated the CMC from the blend while increasing the ensemble mean proportion to 60 percent by Days 7-8. ...Weather/Hazards Highlights... A lingering surface low and energy over the Gulf of Alaska should cause some moderate precipitation across Southeast Alaska into the weekend. Meanwhile, the system forecast to track across the southern Bering Sea/Aleutians should spread a broad area of precipitation and strong winds (especially to the south of the low track) across that region for the weekend. Winds could reach storm force at some locations within the axis of strongest winds, likely over marine areas. Gradual weakening of the surface low as it tracks across the Alaska Peninsula and settles into or near the Gulf should reduce wind speeds with time, though the Aleutians/Alaska Peninsula may see a period of brisk northwesterly winds behind the system. Beyond the Aleutians, moisture from this system should extend across the far southwestern mainland/Alaska Peninsula and then the southern coast plus the Panhandle, with the latter seeing the highest totals around Sunday-Monday. Also over the course of the period, an upper trough currently forecast to deepen over the northwestern mainland should push a front southeastward across the state. The upper trough/front could generate some areas of light snow. Into the weekend, expect highs to be above normal over the North Slope and below normal over the Panhandle and parts of Southcentral, with a mix of anomalies in-between. Most areas should see above normal morning lows. Temperature trends from late weekend into the first half of next week will depend uncertain flow details aloft. Currently the most likely scenario is for a deepening upper trough over the northwestern mainland to promote a colder trend from west to east, bringing temperatures down to below normal levels especially over western-central areas by next Monday-Wednesday. Tate/Rausch 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