Alaska Extended Forecast Discussion National Weather Service College Park MD 624 PM EDT Mon Sep 8 2025 Valid 12Z Fri 12 Sep 2025 - 12Z Tue 16 Sep 2025 ...Heavy rain threats into parts of coastal Southcentral Alaska later this week, and again by next Tuesday... ...Overview... An upper low over northern Alaska will retreat northward later this week as upper ridging nudges westward across the Mainland. An initial weakening surface low over the Gulf which should continue to bring a threat for moderate to heavy rainfall for the Southern Coast region late this week. A shortwave moving across the Aleutians should spin up another deeper surface low into the Gulf by early next week, which may prove slower to move with the upper ridge becoming stronger and more blocky. This brings another period of heavy rainfall to much of the Southern Coast and possibly into parts of the Southeast. A third surface low looks to skirt the western to central Aleutians late period. ...Guidance Evaluation/Preferences... Overall, the 12z deterministic solutions for today showed good agreement at least on the larger scale through the entire period, but plenty of uncertainty in the details. The main feature of interest is the shortwave across the Aleutians which amplifies sending a surface low into the Gulf early next week. The GFS and ECMWF seemed to form the better consensus on this evolution with the ensemble means. The GFS however, seems to favor development of a triple point low this weekend which shows a much faster/more easterly position with the cold front mid to late period. The WPC forecast today favored more weighting towards the ECMWF with more contributions from the ensemble means later in the period to help smooth out the detail differences. ...Weather/Hazards Highlights... The initial system weakening in the Gulf should promote lingering breezy conditions over favored areas across the AKPen on Thursday, with modest to heavier rain eastward across coastal Southcentral to around Yakutat. This area will see the greatest moisture surge ahead of the cold front combined with enhanced lift from the terrain. Rainfall totals of a few inches are possible along the coast with several inches (3-6"+) toward Yakutat per the NBM/models. For the rest of the Interior, scattered showers will linger through the period. The next surface low may bring some scattered showers to the eastern Aleutians and Alaska Peninsula region, but as deepens moisture lifts northward ahead of the cold front as it moves into the Gulf around next Monday or Tuesday, another heavy rainfall threat looks to develop for mainly the Southern Coast region and possibly northern Panhandle. Gusty winds are possible as well depending on how deep the low gets and the resulting pressure gradient across the region. Temperatures over much of the Mainland (except coastal Alaska and the Panhandle) will begin the period below normal but moderate to above normal by the weekend and early next week as upper ridging builds over the state. Below normal temperatures may hold a little longer over the North Slope region. 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