Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
748 PM EDT Mon Mar 17 2025

Valid 12Z Fri 21 Mar 2025 - 12Z Tue 25 Mar 2025

...Overview...

With the typical differences/continuity adjustments, guidance 
continues to show multiple waves reaching into the Northeast 
Pacific/Gulf of Alaska late this week into the start of next week.
These systems will produce unsettled weather (though mostly light
to moderate precipitation totals) along the southern coast and 
Panhandle while flow to the north/west should produce some brisk 
to strong winds over the Aleutians into Alaska Peninsula. Guidance
continues to show amplification of the Pacific/Bering Sea upper 
pattern by Sunday-Tuesday as a ridge builds into the 
Aleutians/Bering Sea to support a digging trough over the east- 
central Pacific. This should ultimately lead to farther south low 
pressure emphasis over the eastern Pacific by next Tuesday. 
Meanwhile the ridge will give an eastward push to an initial 
trough extending to the southwestern coast from an eastern Siberia
upper low. A surface ridge over high latitudes of the Arctic will
help to maintain brisk easterly winds across the North Slope but 
the gradient may finally slacken early next week. Below normal 
temperature anomalies near the western coast should expand a 
little eastward by early next week while most other areas should 
see near to above normal temperatures.

...Model guidance and predictability assessment...

Guidance maintains reasonable agreement and continuity with the 
larger scale aspects of the Pacific/Gulf of Alaska pattern, though
with various issues with lower predictability details. Models 
have been exhibiting greater difficulty with details of the 
eastern Siberia upper low and the trough extending to its 
southeast (including the digging energy so the south from the 
weekend into early next week) as well as for the ridge that builds
into the Aleutians and Bering Sea.

For low pressure initially near the southern Gulf of Alaska, 
today's consensus has shifted a little southward from yesterday 
(thus trimming or delaying associated precipitation along the 
southern coast). There are still small-scale details that will 
take into the short range period to resolve. Upstream there is 
still good initial continuity and agreement with the system south 
of the Aleutians, and the idea that one or more leading frontal 
waves will reach into the northeastern Pacific/Gulf while the 
parent low drops southeast. By around Saturday the 12Z/18Z GFS and
12Z UKMET show a compact wave farther north near the eastern 
Aleutians versus most other guidance and by Sunday the UKMET shows
its best defined surface low near Kodiak Island instead of 
farther east-southeast. A separate weaker wave could be near 
Kodiak Island though.

Meanwhile, 12Z ECMWF/CMC runs have adjusted somewhat northward 
with the initial eastern Siberia upper low to reach closer to 
GFS/UKMET runs that have been on that side of the spread. This 
raises heights some within the trough extending to its southeast. 
Machine learning (ML) models have also been favoring some 
northward drift. As energy flowing underneath the low begins to 
dig in response to the building ridge approaching from the west, 
ML models in principle offer strong support for the ensemble means
which have been depicting a sharpening but weakening open trough 
that pushes into the western mainland early next week. Latest GFS 
runs and the 12Z ECMWF are close to this scenario.

Differences are greater just to the west, as GFS runs have tended
to hold the ridge westward of other guidance including the ML 
models (which on average show the upper ridge axis reaching near 
170W longitude by early next Tuesday). This tendency is much less 
pronounced in the GEFS, and the new 18Z GFS looks better. CMC runs
and eventually to a lesser extent ECMWF may be overdone with 
eastward progress of a frontal system (aside from the leading warm
front). Most ML models favor a solution closest to the ensemble 
means here as well.

A 12Z model composite consisting of 40 percent ECMWF and the rest
split among the GFS/UKMET/CMC provided a good representation of 
significant features early in the period, with Day 6 Sunday 
starting to incorporate some of the ensemble means (12Z 
GEFS/CMCens and 00Z ECens) to temper details that become 
questionable in the non-ECMWF guidance. Then by Days 7-8 early 
next week the forecast adjusted to 60-80 percent means with the 
ECMWF providing the only operational model input, given the 
overall ML model support for a solution closest to the means.

...Sensible weather and potential hazards...

The southern coast and Panhandle should see unsettled weather for
most of the period with waves reaching the Northeast Pacific/Gulf
of Alaska late this week into the start of next week. These waves
should gradually trend weaker with time and better low pressure 
emphasis will likely shift farther south over the eastern Pacific 
by next Tuesday. Expect mostly light to moderate precipitation 
while each wave may provide some wind enhancement along coastal 
areas and open waters. It will take additional time to resolve 
low-predictability specifics of the waves and thus the finer 
precipitation details. Flow behind the Pacific low pressure 
systems may produce periods of brisk to strong northerly winds 
over the Aleutians and into the Alaska Peninsula, most likely 
during Saturday-Monday. Portions of the western mainland may see 
scattered light snow late week into the weekend along a persistent
wavy surface front that should begin to push eastward around 
Sunday. Flow around high latitude Arctic high pressure will 
maintain brisk to strong easterly winds across the North Slope 
through the weekend. Guidance differs on specifics of the surface 
pattern by early next week but suggests potential for the gradient
to slacken some to yield lighter winds. Returning to the 
Aleutians, guidance still shows a surface ridge bringing more 
tranquil conditions from west to east by Sunday-Monday. Southerly 
winds should strengthen over the western Aleutians early next week
ahead of low pressure forecast to track near Kamchatka.

The upper trough extending southeast from an eastern Siberia 
upper low will keep temperatures somewhat below normal near the 
western coast of the mainland. Expect the below normal anomalies 
to push eastward somewhat late weekend into early next week 
(ultimately covering the southwestern quadrant of the mainland) as
the upper trough axis moves eastward. The remainder of the 
mainland should trend somewhat warmer with near to above normal 
temperatures. Expect warmer anomalies for morning lows relative to
those for daytime highs. The Panhandle should maintain a more 
narrow than usual temperature range with above normal morning lows
and below normal highs.

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