Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
559 PM EST Wed Nov 27 2024

Valid 12Z Sun Dec 1 2024 - 12Z Thu Dec 5 2024

...General Overview...

A blocky upper level flow pattern is expected to be in place
across the Alaska domain for the weekend after Thanksgiving, with
a cut-off upper high over eastern Siberia.  A well defined upper
low pinches off from the broader trough axis that will be in place
across over northwestern Canada Saturday, and then retrogrades
southwestward towards the southern Bering and just north of the
Aleutians around the upper high by Monday morning.  This upper low
is expected to spur surface cyclogenesis south of the Alaska
Peninsula by the middle of next week.  Across mainland Alaska, an
arctic air mass will be in place, and this should gradually modify
some going into next week.  A +PNA pattern is expected to be in
place across western Canada with an upper ridge axis in place
across British Columbia.

...Guidance Evaluation/Preferences...

The 12Z model guidance suite features reasonably good synoptic
scale agreement across the Alaska domain on Sunday, with good
overall clustering with the upper low crossing southwest across
Alaska through the weekend.  The models are also in good agreement
with the upper high situated across the western Bering and far
eastern Siberia, and this high then weakens and moves westward for
early in the week.  Similar to yesterday, the region with the
greatest model differences is across the Gulf region and the
timing of multiple shortwave impulses around the main upper level
low that will affect the southeast portion of the state.  Model
differences become more widespread and significant going into next
Wednesday-Thursday, and thus the ensemble means accounted for
about half of the model blend by that time.

...Weather/Hazards Highlights...

Periods of moderate to heavy rain are expected to make weather
headlines across the southeast Panhandle for the first few days of
December as a potential atmospheric river event sets up and brings
several inches of rainfall across the windward terrain.  This may
lead to enhanced run-off and rises on area rivers.  The heaviest
rainfall is likely to be on Monday, and mainly near the Ketchikan
region.  Given the milder conditions expected here, snow levels
will be higher and most population centers will get mainly rain. 
Additional rainfall is expected going into the middle of the week
as well.  Farther west, heavy precipitation is possible for the
windward facing terrain of the southern Alaska Peninsula and the
Kenai Peninsula, particularly during the middle of next week. 
Elsewhere across the state, the majority of the mainland should
remain dry north of the Alaska Range.  There may be some gap winds
that develop across portions of the Alaska Peninsula and points
eastward for the first half of the week, depending on how the
surface lows evolve to the south.  Frigid temperatures are
expected for much of the Interior and the Brooks Range, with
overnight lows dropping into the -10s to -20s through Monday, and
highs only recovering about 10 ten degrees from those lows.  The
good news is a moderating trend is likely to commence going into
early to middle next week as the upper ridge axis from western
Canada tries to build in, and more of a maritime influence
develops across southern Alaska.

Hamrick

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