Alaska Extended Forecast Discussion National Weather Service College Park MD 700 PM EDT Fri Jul 18 2025 Valid 12Z Tue 22 Jul 2025 - 12Z Sat 26 Jul 2025 ...Some heavy rain possible in eastern portions of the Mainland next week... ...Overview... An upper low is forecast to be centered over the Bering Strait at the start of the period Tuesday and slowly drift southeastward over Mainland Alaska, reaching the Gulf of Alaska by late next week. Moisture will be drawn up into and ahead of this low, leading to moderate to heavy rain especially across eastern portions of the Mainland--namely the eastern half of the Brooks Range/North Slope and the Copper River Basin. 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 Tuesday. 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. The main potential model issue arises by next Friday as the 12Z ECMWF lingers a spoke of the upper low/trough farther northwest near the Seward Peninsula. As the GFS, CMC, and the AI models consolidated the energy over the Gulf of Alaska by that point, leaned against the ECMWF. Models are reasonably agreeable that the upper low and a surface low should strengthen a bit once they reach the Gulf of Alaska. Also by later next week, 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 deterministic guidance favoring the ECMWF and GFS early in the period. As the forecast progressed, lessened the proportion of individual models (especially the ECMWF) while introducing and increasing the proportion of the GEFS and EC ensemble means to about half Day 8 amid the increasing 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 Tuesday and Wednesday, orographic support and lows along the frontal system 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 late Tuesday through Wednesday and lingering into Thursday. The Yukon Flats can expect a minimum in precipitation, and southern coastal areas (including Southeast Alaska) may stay dry until later next week when the upper low is approaching. The Alaska Range may see locally heavy amounts around Tuesday and then peaking again Thursday-Friday with the low overhead. Wet snow is possible in the higher elevations of both the Brooks and Alaska Ranges. Meanwhile, the eastern Aleutians/Alaska Peninsula could see rounds of light to moderate rain. Temperatures will be cooling to below normal for much of the Mainland Tuesday and beyond 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 a warmer than average Tuesday until the low aloft reaches the region. Western Alaska should warm later next week 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