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