Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
601 PM EST Mon Nov 25 2024

Valid 12Z Fri Nov 29 2024 - 12Z Tue Dec 03 2024

...Wet/Snowy pattern setting up for the Southeast/Panhandle by the
Thanksgiving weekend as frigid air prevails across the Interior...


...Guidance Evaluation/Preferences...

Model guidance continues to agree that a blocking omega
upper-level pattern across the Alaskan domain will become more
amplified with time heading into the Thanksgiving weekend.  A
closed anticyclone is forecast to form and meander over
northeastern Siberia while a general storm track extends from
south of the Aleutians toward the Southeast/Panhandle through the
medium-range period.  More specifically, today's deterministic
guidance has again trended toward a stronger ridge axis across the
Bering Sea through the Alaska Peninsula at the start of the
medium-range forecast period midweek.  This stronger ridge appears
to help slowing down the northeastward progression of cyclonic
circulations along the aforementioned storm track, and delay the
arrival of precipitation across the Panhandle during the weekend. 
The ridge axis then detaches into an upper high which meanders
over northeastern Siberia into early next week.

Meanwhile, deterministic guidance today shows increased
uncertainty regarding the details of the individual disturbances
in the vicinity of the storm track.  The ensemble means generally
depict that the leading cyclone that is forecast to track south of
the Aleutians late this week will slow down and weaken as it edges
toward the southern coastline and the Panhandle early next week. 
There is a tendency for the models to slow down this system
further as the upper blocking pattern gets established over the
Alaskan domain.  Ensemble means then show good agreement that the
next cyclone moving along the same storm track will reach south of
the Aleutians by next Tuesday.

Today's WPC forecast package for Alaska was based on a consensus
blend of about 40% from the 12Z ECMWF and the 00Z/12Z EC mean, 40%
from the 12Z GFS/GEFS, and 20% from the 12Z CMC/CMC mean,
transitioning to mostly a blend of the ensemble means for Days 7 &
8.  This blend yielded a solution compatible with yesterday's
forecast package, resulting in further lessening of and later
arrival of QPF for the Panhandle during the Thanksgiving weekend.


...Weather/Hazards Highlights...

Persistent northwesterly flow in the upper levels down the right
branch of an omega blocking pattern will maintain mostly clear and
cold conditions for interior Alaska with a cold high pressure
system lifting north into the Arctic Ocean into a ridge axis at
the surface.  Passing shortwave energy could develop a front and
bring some snow showers for the North Slope late this week.  Much
of the interior sections will be colder than normal, with low
temperatures possibly dipping to near or below -40 degrees at the
coldest spots in the eastern interior.  Milder than normal
temperatures are forecast for the North Slope as a more
southwesterly flow develops at the surface.

Modest amounts of precipitation associated with a weakening old
cyclone remain across the Panhandle as the medium-range period
begins midweek.  Meanwhile, the distance from the main cyclone
moving across the North Pacific will likely keep the heaviest
precipitation from reaching the Aleutians, although a couple of
days of light to moderate rain under gale-force east to
northeasterly winds can be expected across the southern Peninsula
to the eastern Aleutians by around Thanksgiving.  An increasing
chance of mountain snow and low-elevation rain can be expected to
overspread the Panhandle through the Thanksgiving weekend. 
Precipitation should become heavier early next week as the
offshore cyclone edges closer toward the Panhandle and the
southern coastline although the details remain uncertain at this
juncture.

Kong


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