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