Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
754 PM EDT Thu Apr 3 2025

Valid 12Z Mon 07 Apr 2025 - 12Z Fri 11 Apr 2025

...Heavy coastal rain and mountain snow threats across the 
southern tier of Alaska continue into early next week...


...Overview...

Most guidance shows a general area of mean troughing aloft with 
one or more embedded upper lows from the Arctic through the 
western mainland and into the northeastern Pacific. However there 
is a lot of spread and variability for details within this axis of
lower heights. Even with the spread for specifics aloft, there is
a majority cluster advertising surface low pressure staying close
to the southern coast Monday-Wednesday and maintaining 
rain/higher elevation snow which should be heaviest early in the 
week. The overall area of low pressure may wobble farther 
southeast later in the week, confining organized precipitation 
more to the southern Panhandle. On the western side of the mean 
trough, digging energy may support a wave/front and some light 
snow near the southwestern coast and Alaska Peninsula around 
Monday-Tuesday. Meanwhile western Pacific low pressure will most 
likely track south of the Aleutians late in the week, but with 
some uncertainty for its latitude.

...Guidance/Predictability Assessment...

With the various dynamical and machine learning models differing 
significantly for specifics of energy aloft and where one or more 
embedded upper lows may form/evolve within the overall area of 
mean troughing, the primary objective of the forecast was to 
reflect the most common themes at the surface and aloft.

In particular, a relative majority of solutions show deeper 
western mainland through southern coast/Gulf of Alaska upper 
troughing and low evolution versus latest GFS/GEFS runs, keeping 
Gulf surface low pressure much closer to the coast than reflected 
in the GFS/GEFS. Although the 12Z UKMET keeps its best defined 
upper low well northward over the Arctic like the GFS, it does 
ultimately dig some stronger dynamics southward like most other 
guidance so its Gulf surface low fits within the non-GFS cluster. 
Also of note, the majority cluster shows lower surface pressures 
over the North Slope and vicinity versus the GFS/GEFS during 
Tuesday-Thursday.

After midweek there are significant differences to the west as 
well, with GFS runs lifting northwestern/northern Pacific low 
pressure farther north into the Aleutians while in turn displacing
the northwesterly flow aloft seen over the eastern Bering Sea in 
other guidance. At least the 12Z and 18Z GFS runs represent a more
suppressed surface trend compared to earlier versions that pushed
a frontal system well into the Bering Sea. 00Z/06Z machine 
learning models also favored a suppressed track south of the 
Aleutians, albeit with various details, though a couple 12Z ML 
models have lifted a bit northward.

In order to reflect primary guidance themes while downplaying 
very uncertain specifics, the early-mid part of the forecast 
started with an even blend of the 12Z ECMWF, 00Z ECens mean, 12Z 
CMC, 12Z CMCens mean, and 12Z UKMET. After Wednesday the CMC 
strayed to the deep and persistent side of the spread with its 
western mainland upper low, so Thursday-Friday started with 30 
percent 12Z ECMWF and the rest 12Z CMCens/00Z ECens means. The new
12Z ECens mean conformed to the main aspects of the preferred 
blend.

...Weather/Hazards Highlights...

Upper dynamics and surface low pressure near the southern coast 
of the mainland should continue coastal rain and inland/higher 
elevation snow over the far south and Panhandle into early-mid 
week. Expect heaviest activity to extend from the weekend into 
Monday, with the Days 3-7 Hazards Outlook depicting an area from 
the far eastern tip of the Alaska Peninsula to the far northern 
Panhandle valid Sunday-Monday. Precipitation should trend lighter 
after Monday but with continued uncertainty for specifics. Some 
areas of lighter and more scattered precipitation (mostly snow) 
may extend farther north over the mainland. A wave dropping 
southeastward could bring a brief period of light snow to the far 
southwestern mainland/Alaska Peninsula around Monday-Tuesday. The 
overall pattern should produce brisk northwesterly winds over and 
near the Alaska Peninsula early-mid week but with speeds likely 
staying below hazardous criteria. The Aleutians could see some 
influence from North Pacific low pressure after midweek, 
depending on the system's latitude.

The upper trough forecast to be over the western mainland at 
least through midweek will support below normal temperatures over 
the western half or so of the state while the east remains above 
normal. Anomalies for morning lows should be warmer than those for
daytime highs. While some degree of upper troughing may persist 
later in the week, it should at least trend weaker and allow 
temperatures over the west to return closer to normal. 

Rausch


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