Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
757 PM EDT Sat Mar 15 2025
Valid 12Z Wed 19 Mar 2025 - 12Z Sun 23 Mar 2025
...Overview...
Most of Mainland Alaska should see southerly flow or some degree
of upper ridging while an upper low near the Bering Strait as of
early Wednesday wobbles westward into or near eastern Siberia.
Some degree of troughing will likely persist near the southern
half of the western coast of the mainland. To the south, expect a
wave reaching the east-central Gulf of Alaska around midweek to
bring a brief episode of enhanced winds/precipitation to the
Panhandle. This wave will quickly give way to a couple fairly
progressive upstream systems. The first will track eastward from
the southern Bering Sea while the second should stay south of the
Aleutians. These systems will tend to keep the southern coast and
Panhandle unsettled during the period with some periods of brisk
winds over the Alaska Peninsula and Aleutians as well. Ridging
over high latitudes of the Arctic will help to maintain breezy
conditions across the North Slope. The forecast pattern evolution
should promote some warming over most areas, though proximity of
upper troughing may keep far western areas relatively cooler.
...Model guidance and predictability assessment...
For the wave forecast to be a ways west/southwest of the
Panhandle as of early Wednesday, latest guidance maintains good
continuity from 24 hours ago for its existence while the ensemble
means and machine learning (ML) models are reflecting it better
than they were yesterday. There is still some scatter, with the
12Z ECMWF still a bit on the northeast side of the spread. A
composite approach looks reasonable for this system which should
dissipate before early Thursday.
At the same time, guidance shows unusually good agreement for the
elongated midweek system just north of the Aleutians. Some spread
develops as the system reaches east of the Aleutians/Alaska
Peninsula later in the week, in particular with the ICON and most
ML models nudging the system along faster than the dynamical
model/ensemble mean consensus. Will maintain the depiction of the
dynamical majority while staying alert for any potential trends in
the ML model direction. The main continuity adjustment from
yesterday is a northward trend by Thursday-Friday. Note that the
12Z GFS strays to the western edge of the envelope by Friday, with
the GEFS mean more in line with other guidance. The 12Z CMC looks
considerably improved compared to earlier runs that were
suspiciously slow.
There is a relative majority of guidance that has maintained
consistency with the next system which should reach south of the
Aleutians (just south of 50N latitude) by early Friday. The most
common clustering of dynamical/ML guidance (ECMWF/CMC/ICON and
nearly all of the ensemble means) suggests a somewhat southwest-
northeast elongated system reaching south of the eastern
Aleutians/Alaska Peninsula by Saturday and then southeast of the
Alaska Peninsula by next Sunday. Individual ensemble members
exhibit a lot of spread along this corridor though. GFS runs
continue to be a slow extreme with the parent low, favoring
exclusion of that model from the forecast. While the 18Z GFS
remains slow with the main low, at least it introduces a leading
frontal wave that is closer to where other guidance tracks the
primary system.
Guidance continues to show various ideas for what may become of
the upper low to the west of the mainland. ECMWF/CMC runs have
been the steadiest with its persistence while the ensemble means
maintain troughing but suggest that the initial upper low could
lift northwestward with time. A number of ML models also depict
this northwestward drift. GFS runs have tended to lift out the
upper low fairly quickly but the new 18Z run uses upstream energy
to reform another low within the mean trough. For now prefer to
lean toward greater persistence of an upper low until there is
stronger clustering toward the alternative.
Today's array of guidance supported a 12Z model composite early
in the period (slightly more GFS/ECMWF relative to the CMC/UKMET).
Then by Day 6 Friday the forecast replaced the GFS with the GEFS
mean since the latter compared much better to the majority cluster
for both system of interest at that time. Then the forecast for
next weekend utilized half ECMWF/CMC and half 12Z GEFS/00Z ECens
means to reflect preferences for the North Pacific and flow
over/west of the mainland.
...Sensible weather and potential hazards...
Low pressure tracking northward toward the east-central Gulf of
Alaska on Wednesday and its leading wavy front will support a
brief episode of enhanced precipitation over the Panhandle, with
potential for some brisk to strong winds along and offshore
coastal areas. An upstream system tracking from the southern
Bering Sea into the Gulf will bring mostly light precipitation to
the Aleutians on Wednesday and then maintain some flow of
moisture into the southern coast. Totals over the southern coast
from this system and preceding moisture should be in the moderate
range, with precipitable water values somewhat above climatology
but not to an exceptional degree. Most precipitation with the
upstream North Pacific system should stay just south of the
Aleutians. How much moisture reaches the southern coast by next
weekend will depend on storm track details that will take some
additional time to resolve. Flow behind the latter two systems may
produce periods of brisk to strong northerly winds over the
Aleutians and possibly into the Alaska Peninsula. Portions of the
west-central and north-central mainland may see light/scattered
snow around Wednesday, with some light activity possibly lingering
over the far southwest during the weekend. Flow around high
latitude Arctic high pressure will maintain brisk to strong winds
across the North Slope.
Nearby upper troughing with an embedded low should keep
temperatures somewhat below normal toward the western coast of the
mainland. The remainder of the mainland should trend somewhat
warmer but with some uncertainty over the coverage of above normal
readings. Expect warmer anomalies for morning lows relative to
those for daytime highs. The Panhandle should continue to see
near to below normal highs but with morning lows above 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