Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
656 PM EST Sun Feb 20 2022
Valid 12Z Thu Feb 24 2022 - 12Z Mon Feb 28 2022
...Heavy precipitation along the southern coast of the mainland
continuing at least through Thursday-Friday...
...Overview...
Today's guidance once again shows a broad region of cyclonic flow
between a mean low near Kamchatka and a very amplified upper ridge
settling into Canada and the Arctic. There is relative agreement
that this pattern will support multiple days of precipitation,
heavy at times, focused along the southern coast of the mainland.
Some moisture could eventually reach the Panhandle. Many areas
will also see above normal temperatures, with much above normal
readings most likely over the northwestern half of the mainland.
There is still considerable uncertainty regarding individual
shortwaves and surface systems/fronts across the North Pacific
into Gulf of Alaska and Bering Sea though.
...Guidance/Predictability Assessment...
The forecast maintained a blend approach to emphasize the most
similar aspects of the large scale pattern and some embedded
features while downplaying less confident aspects. As in recent
days, the 12Z operational models provided the starting point for
the first half of the period while 12Z GEFS/00Z ECens weight
quickly increased to 40-50 percent total by days 7-8 Sunday-Monday.
During the first half of the period the primary focus will be on
low-predictability shortwave details that will affect one or more
surface waves expected to track over an area encompassing the
North Pacific through Alaska Peninsula and Bering Sea. The best
signal at the moment is for one wave to track over this area
Thursday into Friday and then for a second wave that may track
somewhat farther east (perhaps near Kodiak Island) as shortwave
energy may elongate a little eastward by Friday-Saturday.
ECMWF/ECMWF mean runs have been weaker and faster with the latter
feature than most other models/means, but at least share the more
general idea of a front with a leading band of enhanced winds
advancing across the Gulf of Alaska.
By later in the weekend and early next week the surface pattern
should relax somewhat along the southern coast while a system
develops upstream over the Pacific, with the supporting upper
trough forecast to reach near 150W longitude by next Monday. Over
the past day the best clustering of guidance has gravitated
somewhat southward with this system which is toward yesterday's
GFS. There is a moderate amount of north-south spread for this
system which is expected to be south of Kodiak Island by next
Monday. Also at that time guidance is showing a strengthening
system that may begin to influence the western Aleutians early
next week. Ensemble means are very similar while operational
models show typical spread for specifics.
...Weather/Hazard Highlights...
Guidance is maintaining the general signal for a period of locally
heavy precipitation along the southern coast during the latter
half of the week, focused by an area of brisk to strong winds
across the Northeast Pacific/Gulf of Alaska. Important surface
wave/front details will take additional time to resolve due their
relative small scale leading to low predictability. Today there
appears to be somewhat better potential for meaningful
precipitation to extend into the southeastern coast and Panhandle
by late week and the weekend, with some moderate to heavy activity
possible. Highest totals for the overall period should be near
the Kenai Peninsula. Some moisture may extend farther north over
the mainland but with much lower totals. Precipitation should
trend lighter by Sunday-Monday. A strengthening system may bring
increasing winds/precipitation to the western Aleutians by next
Monday.
The forecast continues to show above to much above normal
temperatures over most of the state through the period. The
greatest anomalies of plus 20-30F, and over some areas even
warmer, are most likely over the northwestern half of the
mainland. The primary exception to this warmth will be moderately
below normal highs over the southern two-thirds of the Panhandle.
In general expect the anomalies for min temperatures to be
somewhat warmer relative to those for the 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