Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
653 PM EST Tue Nov 09 2021
Valid 12Z Sat Nov 13 2021 - 12Z Wed Nov 17 2021
...Overview and Guidance Evaluation/Preferences...
This weekend, the pattern over Alaska will be characterized by
slow-moving troughing aloft extending over the central/eastern
mainland and into the northeastern Pacific, while upper ridging
moves in behind. At the surface, a low over the Gulf of Alaska
will migrate eastward while another surface low tracks northeast
through the northeastern Pacific, consolidating likely just south
of the Panhandle by Sunday night. A surface high is forecast to
strengthen over the central/northern mainland into the early part
of next week. This weekend pattern appears to have reasonable
agreement amongst the model guidance. Though, some differences
arise with yet another surface wave moving northeast through the
Pacific toward the southern Panhandle by Monday, as shown by the
GFS runs but not really in other guidance. But overall a
multi-model blend of the 12Z deterministic guidance (ECMWF, GFS,
CMC, and UKMET) served as a reasonable starting point for the
forecast through the weekend.
As the workweek begins, guidance somewhat diverges upstream
regarding a negatively tilted upper trough coming into the Bering
Sea. Overall this system and its associated surface low/frontal
system seems to be trending faster. The ECMWF runs and the EC
ensemble mean take a slower/southern track, which was somewhat
closer to WPC continuity. This is eventually leads to model
guidance being out of phase with one another, even between the 12Z
GEFS and 00Z EC ensemble means over the Aleutians for example by
the end of the period. For day 6-7 (Mon-Tue), attempted to split
the difference initially with a middle ground track of the
troughing and surface low, with some incorporation of the EC and
GEFS means as well as the deterministic 12Z ECMWF, GFS, and CMC.
By Day 8/Wed, ended up with a fronts/pressures model blend that
was 50% EC mean, 20% GEFS mean, and 10% each EC/GFS/CMC. Note the
new 12Z EC ensemble mean appears to have a faster track than the
00Z run but not as fast as the GEFS mean, supporting this blend.
...Weather/Hazard Highlights...
Precipitation could linger into Saturday after a wet day in the
Panhandle on Friday with moist inflow from a low pressure system.
Then depending on the exact track of the next low system moving
through the northeastern Pacific, enhanced precipitation may be
possible for southern parts of the Panhandle by Sunday-Monday, but
most may stay south into western Canada. Light to moderate
precipitation is likely along with some possibly enhanced winds
over the Aleutians by early next week with the frontal system.
Below normal temperatures will be most pronounced in terms of
anomalies and persistence over the southwestern mainland, somewhat
easing by around next Wednesday. Meanwhile, the North Slope should
see above normal readings (especially for lows) through the
forecast period. The eastern mainland and Panhandle will initially
see highs not too far from normal and lows above normal, followed
by a cooling trend toward more below normal temperatures.
Tate
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
Hazards:
- Heavy precipitation across portions of the Alaska Panhandle,
Fri, Nov 12.
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