Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
644 PM EST Sat Feb 19 2022
Valid 12Z Wed Feb 23 2022 - 12Z Sun Feb 27 2022
...Heavy precipitation likely along the southern coast of the
mainland next week...
...Overview...
Most guidance continues to show similar ideas for the large scale
pattern evolution from midweek through next weekend. Consensus
shows an amplified upper ridge, from the eastern Pacific through
the mainland and building into the Arctic as of midweek, drifting
eastward into western Canada while a mean upper low likely travels
from the northwestern Pacific into the western Bering Sea and
possibly retrogrades to west of Kamchatka by next weekend. A
broad region of cyclonic flow between these dominant features
should contain multiple shortwaves/possible upper lows with
corresponding surface lows and frontal systems. Within this
pattern, a band of enhanced winds migrating across the
northeastern Pacific should focus significant precipitation from
the Alaska Peninsula through the Kenai Peninsula/Prince William
Sound region mid-late week. Some precipitation may continue along
the southern coast through next weekend but with greater
uncertainty for the details.
...Guidance/Predictability Assessment...
The latest array of guidance again recommended an approach of
emphasizing the 12Z operational models for the first half of the
period (Wednesday into early Friday) followed by incorporation of
12Z GEFS/00Z ECMWF means whose total weight reached 40-50 percent
by the weekend. During the mid-late week time frame, models
continue to suggest a series of waves tracking from the North
Pacific into the eastern/northern Bering Sea, possibly brushing
the southwestern mainland if the track is on the eastern side of
the envelope. These waves and supporting dynamics are very small
in scale and thus have low predictability, but will be important
in refining the specifics of wind/precipitation focus into the
Alaska Peninsula and locations farther to the east. By next
weekend the guidance displays some additional divergence for the
shape of Bering Sea into northeastern Pacific cyclonic flow and
the upper ridge to the east, with continued potential for one or
more surface lows over the North Pacific/Gulf of Alaska and
vicinity. The favored blend ultimately reflected what has been
good consensus for a front reaching the eastern Aleutians early
Wednesday, leading into a combination of fronts/waves Thursday and
some signal for low pressure just south of the Alaska Peninsula by
early Friday. This wave may track northwestward thereafter,
followed by another system that could approach the Alaska
Peninsula around next Sunday. The latter has some relative
support from the latest ensemble means but confidence is too low
at this time to depict as strongly as in the past couple ECMWF
runs and farther south GFS.
...Weather/Hazard Highlights...
A band of brisk to strong winds will migrate eastward across the
North Pacific/Gulf of Alaska and eastern Bering Sea/western
mainland mid-late week, ahead of an initial front early Wednesday
with additional waves and fronts thereafter. The flow of Pacific
moisture will focus significant precipitation over the Alaska
Peninsula and extending eastward at least through the Kenai
Peninsula. Some of the moisture could spread farther north into
the southwestern mainland with lesser totals. Confidence remains
fairly low regarding the specifics of individual surface waves
that would have an important influence on precipitation/wind
details. From about Friday into the weekend there is also
decreasing confidence in larger-scale aspects of precipitation.
These include how much moisture continues eastward into the
southeastern coast and Panhandle, and whether another system could
begin to increase activity once again over the eastern
Aleutians/Alaska Peninsula by next Sunday.
Above to much above normal temperatures will prevail over most of
the state through the period, with best potential for plus 20F and
greater anomalies over northern and western portions of the
mainland. The primary exception to the warm theme will be the
southern two-thirds of the Panhandle which will likely see below
normal highs on most days.
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