Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
647 PM EST Thu Feb 17 2022
Valid 12Z Mon Feb 21 2022 - 12Z Fri Feb 25 2022
...Overview...
Guidance generally agrees that mean upper ridging will prevail
from the eastern Pacific through Alaska and northwestern Canada
for most of next week. A Bering Sea/Aleutians shortwave (with
associated surface system) should briefly dampen the upper ridge
over the mainland as it passes through around Tuesday. Meanwhile
a deep and broad system will likely track over the far
northwestern Pacific toward the western Bering Sea, with one or
more leading surface fronts sweeping across the Bering
Sea/Aleutians. There could be one or more waves
anchoring/embedded within these fronts as well. By the latter
half of the week a fairly strong gradient could set up over the
Alaska Peninsula and western mainland, between these fronts and
high pressure moving from the mainland into western Canada. The
combination of the early-week system and the evolving pattern
mid-late week should focus highest precipitation totals across the
Alaska Peninsula and farther east along the southern coast.
...Guidance/Predictability Assessment...
During the first half of the period, the primary consideration was
to keep the 12Z CMC out of the starting blend for today's forecast
as it was deeper and farther west (near Bristol Bay into the
southwestern mainland) with a potential wave that other guidance
depicts as a weak feature tracking near the southern coast. There
are still timing differences for the system tracking out of the
northern Bering Sea (ECMWF remains slowest) with the ensemble
means supportive of their respective parent models. An
intermediate solution seems reasonable given the array of guidance.
For the latter half of the work week, consensus agrees on the
upper ridge rebounding over the mainland. Ensemble means have
been trending noticeably stronger with the ridge over the past
couple days, supporting a reasonable component of operational
guidance which is mostly stronger than the means aside from the
CMC--which in this time frame happens to have an Arctic upper
low/trough that does not compare well to most other solutions.
Toward Thursday-Friday the recent operational model runs suggest
increasing uncertainty over the shape and exact location of the
upper ridge along with details of any shortwave energy that could
either push into it from the east (an option that seems to be
decreasing in potential) or from the North Pacific. There are
also various ideas for individual waves that could track from the
North Pacific through the eastern Aleutians/Alaska Peninsula and
into the eastern Bering Sea.
Above preferences led to emphasizing the 12Z ECMWF/GFS/UKMET (from
more to less weight) for the first half of the week, followed by
trending to 40 percent total 12Z GEFS/00Z ECMWF mean weight late
in the forecast while keeping 12Z ECMWF input and splitting the
GFS among its 12Z and 06Z runs. This reflected a general signal
for some North Pacific into Bering Sea waviness into Thursday
while becoming more conservative with specifics by Friday.
...Weather/Hazard Highlights...
Expect two main episodes of significant precipitation next week.
The first will be ahead of an upper shortwave/frontal system
pushing eastward from the Bering Sea/Aleutians. Best focus should
be from the eastern Alaska Peninsula/Kodiak Island to the Kenai
Peninsula and possibly parts of the southwestern mainland on
Monday, with meaningful totals extending mostly east of the Kenai
Peninsula into the Panhandle by Tuesday. Then a fairly strong
gradient ahead of an initial front crossing the Bering
Sea/Aleutians should settle into an area from the North Pacific
into the eastern Bering Sea/western mainland by mid-late week,
leading to a precipitation focus over the eastern Aleutians and
Alaska Peninsula as well as possibly some locations farther
eastward. Any surface waves within this flow could bring added
precipitation/wind enhancement to the east of their track.
Uncertainty with specifics of upper ridging and surrounding energy
late in the week leads to low confidence for how much moisture may
eventually reach the southeastern coast and Panhandle.
Above to well above normal temperatures should prevail over the
majority of the state overall, with some exceptions. These
include the central latitudes of the mainland where readings may
drop below normal for a time around Tuesday or Wednesday after the
passage of an upper shortwave/surface front as well as the
southern two-thirds of the Panhandle which should be below normal
for highs during most of the week. In both areas the lows are
likely to have somewhat warmer anomalies.
Rausch
Hazards:
- Heavy precipitation across portions of mainland Alaska, Mon, Feb
21.
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