Alaska Extended Forecast Discussion National Weather Service College Park MD 742 PM EDT Sat Jul 19 2025 Valid 12Z Wed 23 Jul 2025 - 12Z Sun 27 Jul 2025 ...Rounds of rain, possibly heavy, across the Mainland next week... ...Overview... An upper low is forecast to be centered over the Bering Strait at the start of the period Wednesday and slowly drift southeastward over Mainland Alaska, reaching the Gulf of Alaska by late week. Rounds of moisture are likely in conjunction with this low, leading to moderate to heavy rain in eastern portions of the Mainland through midweek, as well as possibly the Y-K Delta to Alaska Range during the latter part of the week. Temperatures are forecast to cool below average in most areas due to the lowering heights aloft. ...Guidance Evaluation/Preferences... Individual model and ensemble guidance is pretty agreeable with the large scale pattern described above. The pattern is quite blocky with an upper high over the northeast Pacific and another in the Arctic Ocean, with Alaska's upper low in between. Models remain consistent that the centroid of the upper low should be located over the Bering Strait into Wednesday. After that, troughing should extend east/southeast across the Mainland with the upper low slowly tracking in the direction of the trough. There is some model spread with the details of the lobes of vorticity within the broad trough, but nothing out of the ordinary for the extended range. No particular outliers were seen, aside from the UKMET by Friday that showed combining energies near the Chukchi Sea that prevented the upper low from diving southeastward like the other guidance. Models are agreeable with the upper and surface lows deepening by next weekend when they reach the northeast Pacific/Gulf of Alaska. Meanwhile upper ridging is forecast to build over the Aleutians and Bering Sea, as the southeastward moving upper low reorients the northeast Pacific upper high to the west. The WPC forecast used a multi-model blend of the GFS, ECMWF, and CMC early to mid period. As the forecast progressed, used some GEFS and EC ensemble means in the blend, but was able to maintain a majority of deterministic models throughout, given the relatively low spread. This solution generally showed good continuity from yesterday's forecast. ...Weather/Hazards Highlights... Moist inflow linked with the low aloft and a surface frontal system moving through will allow for broad precipitation chances across the Mainland next week. Into Wednesday, orographic support and the frontal system's surface low should allow for precipitation to be moderate to locally heavy for the central and eastern Brooks Range and possibly reaching the North Slope. The persistence of this precipitation could lead to heavy amounts accumulating over time. Similarly, a wave of low pressure forming along the cold front in the southeast Mainland/Copper River Basin could enhance rainfall there through Wednesday, though with less chance today of it lingering into Thursday. The Yukon Flats can expect a minimum in precipitation, and southern coastal areas (including Southeast Alaska) may stay dry until later in the week when the upper low is approaching. Then another round of precipitation is forecast with the low overhead, with moderate to possibly heavy rain amounts in the Y-K Delta around Thursday and moving east, for enhanced totals in the Alaska Range. Wet snow is possible in the higher elevations of both the Brooks and Alaska Ranges. Fortunately the rain chances combined with cooler temperatures will help ease the fire weather season. As the surface and upper lows restrengthen in the northeast Pacific into next weekend, Southeast Alaska could start to see heavy precipitation. Meanwhile, the eastern Aleutians/Alaska Peninsula could see rounds of light to moderate rain. Temperatures will be below normal for much of the Mainland mid to late week due to the upper low. Highs should generally be around 5-15 degrees below average, with lows less anomalous. Maximum temperatures will be in the 50s and 60s for most areas. Southeast Alaska (the Panhandle) can expect near to below average temperatures after a warm early week period. Most of the Mainland, especially western parts, should warm up by next weekend as an upper ridge builds atop the Aleutians to Bering Sea behind the main upper low. 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