Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
655 PM EST Mon Jan 17 2022
Valid 12Z Fri Jan 21 2022 - 12Z Tue Jan 25 2022
...Heavy precipitation along the southern coast and Panhandle late
week into the weekend, with a wet pattern continuing into next
week...
...Overview...
Guidance continues to show a very warm and wet pattern as a strong
eastern Pacific mean ridge extends northward into Mainland Alaska
and northwestern Canada while a mean trough axis persists farther
west. Within this trough there should initially be a fairly deep
northern Bering Sea upper low that may influence strong low
pressure expected to track northward along the western coast of
the mainland. Moist flow ahead of this system will focus
significant precipitation across the southern/western parts of the
state with highest totals likely over the southern coast and
Panhandle. Forecast details become more uncertain after the
initial system departs and the overall upper trough gradually
weakens, but there is a general theme that additional significant
precipitation will be possible over some areas between the Alaska
Peninsula and Panhandle through next Tuesday.
...Guidance/Uncertainty Assessment...
The 12Z operational model consensus has trended faster for the
leading system that should track northward near the western coast
of the mainland. At the time of forecast preparation, the 12Z
GEFS/CMCens supported this trend as well. The new 12Z ECMWF mean
has come in close to its operational run. The fast flow aloft
between the deep northern Bering upper low and ridge to the east
seems to support this adjustment.
Remaining forecast details have lower confidence. There is
lingering spread and inconsistency with the ultimate
path/evolution of the northern Bering upper low and surrounding
energy, with some effects on surface evolution across the mainland
during the first half of the period. Meanwhile recent GFS runs
have been fairly much on their own in bringing stronger shortwave
energy and a defined surface wave into the northeastern
Pacific/Gulf of Alaska by around Sunday when most other model/mean
solutions have this area within the gradient ahead of stronger low
pressure farther west. In runs since the 00Z cycle, the 06Z
version was the least extreme so the GFS input for the forecast
exchanged the 12Z run for the 06Z one by Sunday. As for the
aforementioned western system, there is a decent signal for it to
approach the eastern Aleutians by Sunday and then track into the
southeastern Bering Sea. However there is still a lot of spread
for its timing/track/strength as well as for details of yet
another potential system that may or may not interact with it.
A blend of the 12Z operational models provided a good
representation of latest consensus for about the first half of the
period, again with GFS input switching to the 06Z version by
Sunday due to Northeast Pacific/Gulf issues at that time. The
widening spread for details later in the period favored a
conservative approach that included splitting ECMWF input between
the past two runs after Sunday as well as increasing the total
weight of 12Z GEFS/00Z ECMWF mean to 50 percent by day 8 Tuesday.
This blend yielded a Monday-Tuesday evolution of the southeastern
Bering system quickly weakening in favor of the next system to the
south/southeast, but with minimal confidence.
...Weather/Hazard Highlights...
Guidance consistently shows the most pronounced surge of moisture
reaching the state Friday into Saturday, carried by the strong
flow ahead of a storm likely to track northward across the western
Alaska Peninsula and near the western coast of the mainland. The
atmospheric river event should bring the highest totals to the
southern Coast and Panhandle with somewhat greater focus over the
Panhandle by Saturday. Operational models continue to depict
precipitable water values exceeding three standard deviations
above normal over some locations during this episode. Strong
winds will be possible as well, and other areas across the western
and southern mainland may see brisk to strong winds with
terrain-enhanced precipitation. After Saturday the most likely
scenario would have precipitation trending lighter over the
Panhandle for a time while the next system to the west renews
focus of significant precipitation over the Alaska Peninsula and
the southern coast, possibly reaching into the Panhandle by next
Monday or Tuesday. Some moisture may spread farther north as
well. There is a lower potential for a separate wave to prolong
heavy activity over the Panhandle into Sunday before a lighter
trend. The Aleutians will likely see episodes of organized
precipitation and at least brisk winds with individual systems but
with lower than desired confidence in specifics.
To start the period on Friday, the North Slope and far western
parts of the mainland should see below normal temperatures while
above normal readings prevail over most other areas. Then a rapid
warming trend will ultimately bring temperatures up to much above
normal levels over a large portion of the state during the weekend
and early next week.
Rausch
Hazards:
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Thu-Sat, Jan 20-Jan 22.
- Heavy precipitation across portions of mainland Alaska and the
Aleutians, Sun, Jan 23.
- High winds across portions of the Alaska Panhandle and mainland
Alaska, Thu-Fri, Jan 20-Jan 21.
- High winds across portions of mainland Alaska, Sat-Sun, Jan
22-Jan 23.
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