Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
652 PM EST Mon Feb 24 2025
Valid 12Z Fri Feb 28 2025 - 12Z Tue Mar 04 2025
...Overview...
Guidance maintains a mean ridge aloft from the Panhandle and
western Canada into the mainland during the period, with multiple
systems to the south favoring a wet/snowy pattern along and near
the southern coast/Panhandle while drier conditions prevail over
most other areas. The leading system initially south of the
Alaska Peninsula and Kodiak Island on Friday may be accompanied by
strong winds as well, while details of potential trailing systems
have lower confidence. Farther west, most guidance suggests a
fairly strong western Pacific into western Aleutians storm with
leading front may affect the island chain by next Monday-Tuesday.
Temperatures should trend gradually warmer during the period. The
North Slope may remain below normal until late weekend or so,
while the rest of the state should see above to well above normal
readings from late week onward.
...Guidance Evaluation and Preferences...
For the leading system to the south of the Alaska Peninsula/Kodiak
Island as of Friday, the overwhelming majority of dynamical and
machine learning (ML) guidance says that latest GFS/GEFS runs pull
the track of the parent low too far westward--into the Bering Sea
instead of consensus that is over far southwestern mainland and/or
southern Gulf of Alaska by Saturday. From there, even the
majority diverges for specifics of one or more remaining low
pressure centers. An ML model subset offers some support for the
12Z ECMWF/UKMET that maintain some northward progression of a weak
surface low near the western coast through the weekend.
Forecast details become even more uncertain behind this system.
Most runs of latest dynamical models suggest that a wave will
break off from an overall elongated area of low pressure to the
south of the Aleutians, with an ultimate track reaching anywhere
between the eastern Aleutians (12Z UKMET) and the southern
Panhandle (new 18Z GFS). ECens means and what ML models show any
definition with this possible wave favor an intermediate track
into the southwestern mainland/Kenai Peninsula area, most similar
to the 12Z ECMWF.
Per a modest majority of dynamical guidance and decent clustering
of ML models, remaining North Pacific low pressure should
consolidate to the south of the eastern Aleutians/Alaska Peninsula
by Sunday-Monday. As of early next week a compromise among the
12Z ECMWF, 06Z GFS, and latest ECens means (less so the GEFS)
provided the closest depiction of ML model themes. By next
Tuesday even the ML models diverge considerably for what may
happen with the low, ranging between curling back into the Bering
Sea or getting pulled eastward into the Gulf (though the Bering
Sea option would also have a leading front reach into the Gulf).
12Z/18Z GFS runs are faster with the main low and then bring in
another one. A position just south of Kodiak Island for early
next Tuesday, as reflected in the favored blend, has support from
the 12Z ECens mean and ECMWF AIFS that arrived after determination
of forecast preferences.
Based on non-GFS/GEFS preferences for the late week/weekend system
and the most reasonable depiction behind it, the first half of the
forecast emphasized the 00Z/12Z ECMWF runs with modest 12Z UKMET
input. The blend introduced a small weight of the 00Z ECens mean
by Sunday. Then by Monday-Tuesday the forecast shifted to a blend
of 30/20 percent of the 12Z ECMWF/06Z GFS as well as a 30/20
weight of the 00Z ECens mean/12Z GEFS mean. This late-period
blend represented consensus for the system affecting the Aleutians
by that time.
...Weather/Hazards Highlights...
Initially strong but slowly weakening low pressure to the south of
the Alaska Peninsula and Kodiak Island as of Friday will support
enhanced coastal rain and mountain snow along the southern coast
and Panhandle late this week. This storm should also bring strong
winds to the Gulf of Alaska and possibly nearing coastal areas,
leading to adverse boating conditions. Behind this system,
additional lows with below average confidence in specifics should
maintain a fairly wet/snowy pattern along the southern coast and
vicinity. Amidst the detail uncertainty there is a general theme
in the guidance for the best focus to align from the Alaska
Peninsula to the Kenai Peninsula/Prince William Sound by next
Monday-Tuesday. Current guidance does not show exceptional
moisture anomalies but some locally heavy precipitation could be
possible depending on system evolution/track. Much lighter
precipitation may extend into the southwestern mainland at times
while the central/northern part of the state should remain fairly
dry. Around early next week a strong western Pacific into western
Aleutians storm with leading frontal system may spread
precipitation and stronger winds across the Aleutians. At this
time the Days 3-7 Hazards Outlook indicates no areas of
precipitation or wind reaching hazardous criteria.
Expect temperatures to be above normal over a majority of the
state through the period along with a gradual warming trend.
There should be decent coverage of plus 10-20F or greater
anomalies. The North Slope will be an exception, as Arctic high
pressure supports somewhat below normal readings Friday and
lingering over some locations into the weekend before the general
warming trend pushes anomalies above normal by early next week.
Parts of the eastern Interior may be below normal on Friday as
well.
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