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FXAK02 KWNH 212356
PMDAK

Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
756 PM EDT Mon Apr 21 2025

Valid 12Z Fri 25 Apr 2025 - 12Z Tue 29 Apr 2025

...Overview...

The consensus forecast from the Arctic into parts of the mainland
has remained fairly consistent, with an Arctic ridge to the
northwest of the mainland and a central-northern mainland weakness
aloft tending to lift toward the northern coast as ridging builds
in from the southeast. At the surface expect a persistent
gradient between a wavy southern mainland front and Arctic high
pressure. Meanwhile there is continued guidance spread and run-to-
run variability for systems across the North Pacific and into the
Aleutians/southern Bering Sea. One or more of these systems may
bring some focused precipitation to locations between the
Aleutians and the southern coast/Panhandle during the period but
with continued below average confidence for specifics.
Temperatures should remain below average over the north while
above average readings prevail over most southern areas.

...Guidance/Predictability Assessment...

For the system initially over the northeastern Pacific/eastern
Gulf of Alaska as of early Friday, yesterday`s notable shift
toward the northern part of the prior envelope has generally held
up. GFS/GEFS mean runs continue to be south of most other
solutions aside from the 12Z ICON. Latest machine learning (ML)
models favor a solution most similar to the ECMWF cluster. The new
18Z GFS has nudged somewhat northward and the 18Z ICON has
shifted close to the ECMWF cluster too, further improving
confidence.

Behind this system, there is initially some degree of clustering
and continuity with low pressure tracking over the
Aleutians/southern Bering Sea around the end of the week while the
leading wavy frontal system continues eastward to the south of
the Panhandle. However guidance then diverges for the ultimate
evolution/progression of the Aleutians/Bering Sea low and a
potential mid-latitude Pacific system. Dynamical model trends over
the past couple days and 00Z ML models have been suggesting more
emphasis on the Pacific low versus some ensemble means that merge
these systems in some fashion or even emphasize Bering Sea low
pressure as in the 12Z ICONens. Some CMCens/ECens guidance hints
at both features, while CMC runs have been leaning on the
progressive side overall. An added wild card is upper low energy
initially over Siberia. The 12Z ECMWF brings it eastward across
the Bering Sea toward the western coast of the mainland along with
some surface low reflection. Some earlier CMC runs brought the
upper low eastward as well but most other guidance including ML
models are not enthusiastic about such eastward progression of the
Siberia upper low. Preference adjusted to reflect a little more
Pacific low emphasis versus continuity after Saturday, yielding
somewhat more easterly flow over the Alaska Peninsula and toward
the Kenai Peninsula. New 12Z ML models highlight the uncertainty
with this part of the forecast as they are generally less defined
with the primary features.

Farther west the ensemble means and ML models have shown better
agreement and continuity over the past couple days for a system
that will most likely track near or somewhat south of the
Aleutians by next Monday-Tuesday. Operational models vary a lot
more, ranging between having it become overwhelmed by a persistent
leading system by Tuesday versus the slower/larger-scale
evolution of the 12Z CMC. Latest GFS runs and the 00Z ECMWF end up
closest to the ensemble means in principle by the end of the
period even if they may be a tad east and with lower confidence in
their way of getting there.

Adding together the above considerations, today`s forecast for
Friday-Saturday started with a split of 12Z/00Z ECMWF runs and
parts of the 12Z GFS/UKMET/CMC. This reflected non-GFS preferences
over/near the eastern Gulf and a model composite elsewhere. Then
the forecast removed the 12Z ECMWF due to its questionable Bering
Sea evolution while increasing 12Z GEFS/00Z ECens input. Monday-
Tuesday started with 60 percent means and the 40 percent total 12Z
GFS/00Z ECMWF. The ensemble mean weight helped to maintain
reasonable continuity for the northern mainland upper weakness and
the ridge building to its south.

...Weather/Hazards Highlights...

The upper low forecast to linger over the eastern Gulf into
Friday may still produce some light rain and higher elevation snow
over parts of the Panhandle before it finally moves inland by the
weekend. Upstream low pressure over the Aleutians and southern
Bering Sea will bring some light rainfall to that region on Friday
while a leading front may provide somewhat more precipitation
focus (but still light to locally moderate) over the Alaska
Peninsula. From Saturday onward confidence decreases with respect
to the eastward extent of precipitation along the southern coast
as well as for amounts. The favored model/ensemble ultimately
brings moderate totals across most of the southern coast with
potential for some enhancement over eastward-facing terrain. An
upstream system tracking a little south of the Aleutians may bring
another episode of rain early next week. Some of this moisture
could reach as far eastward as the Alaska Peninsula. Lighter
precipitation could extend farther north over southern/western
areas at times. Deep-layer ridging over higher latitudes of the
Arctic will likely support northeasterly or easterly winds of
varying strength through the period.

The northern half to third of the mainland should see below
normal temperatures due to persistent flow around southeast
periphery of the Arctic ridge. Most southern areas will see above
normal readings, though clouds/precipitation should support below
average daytime highs along the southeastern coast into at least
Friday. Anomalies will generally be warmer for morning lows
relative to those for daytime highs. Also expect a gradual warming
trend that will slowly reduce the coverage of below normal
temperatures by next week.

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

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