Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 704 PM EDT Mon Jul 22 2024 Valid 12Z Fri Jul 26 2024 - 12Z Tue Jul 30 2024 ...Heavy rain threat across parts of Alaska late week to next weekend... ...Overview... A deep upper low/trough near or along the West Coast as the period begins Friday will begin the transition from dry and very warm in the short range period to a much colder and wetter pattern in the medium range. Heavy rainfall will be a threat for some across the Mainland as well with this system into this weekend. Some upper level ridging may sneak back into the Mainland behind this early next week and ahead of another trough digging south and east out of eastern Russia and into the northern Bering Sea. ...Guidance Evaluation/Preferences... Models and ensembles show good agreement on timing of the first trough through the Mainland, but some uncertainty still in the details. The greatest differences arise with the next system dropping from eastern Russia around Sunday. The GFS is significantly faster with this system, bringing it into the northern Mainland as early as next Monday. The ECMWF and CMC suggest stronger ridging will build ahead of it over the Mainland and show a much slower transition across the northern Bering Sea. The ensemble means are fairly weak and washed out, given the uncertainties, but do generally favor the slower ECMWF and CMC. However, some of the AI/ML models do support the GFS so this is a highly uncertain forecast still at this time. The WPC progs for today favored a general model compromise for the first few days of the period with good agreement. By day 6 and beyond, began increasing weighting of the ensemble means into the forecast, with some operational ECMWF/CMC to help add some detail and system definition where feasible. ...Weather/Hazards Highlights... As a cold front associated with the initial deep Bering low reaches the West Coast around Thursday or Friday this week, the threat for widespread rains progressing steadily eastward with time increases across the Mainland through at least the weekend. Some of the rainfall could be heavy in spots, especially along/near the Brooks Range and much of the south-central Mainland. Rainfall will progress from west to east across the state with some moderate to locally heavy rain reaching the Panhandle region by next weekend as well. The next trough through the Bering early next week will continue to favor an overall wet pattern, but rainfall intensity at least by Sunday-Monday should be lessening. Well above normal temperatures, with values near or above 80 degrees, will continue through Thursday for parts of the North Slope and eastern Alaska. As strong troughing approaches from the west, this will usher in much cooler temperatures across the Mainland, progressing steadily from west to east into the weekend. Much of Alaska could be 10 to 20+ degrees below normal lasting through at least early next week. Santorelli 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