Heavy Snow in Alaska, November 29 to 30, 2021

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
643 AM AKST Mon Nov 29 2021

.SHORT TERM...Dynamic weather system on the horizon with multiple
low centers already seen on satellite over the distant SW Gulf of
Alaska. The complex Fujiwhara Effect of lows are discussed
further in the long term section below.

The first wave of moisture with an occluded front arrives Monday
afternoon and pushes NE across the panhandle relatively quick.
Most places are cold enough for snow to start, but snow levels
gradually rise to 1000-2000ft in the afternoon for Prince of
Wales and Ketchikan, then 200-1000ft in the Icy Strait region
after midnight. Therefore many locations will see a quick round of
accumulating snow. Greatest snowfall rates will be in the late
afternoon with up to 3 inches in Petersburg and around 4 inches in
the Icy Strait to Juneau region. Hyder has potential to have
greater rates due to proximity of the triple point, so expect 6-9
inches of snow to fall by midnight tonight.

SELY winds will increase this afternoon with the front. Some
places along the outer coast could see gusts close to the strong
wind criteria of 40mph while the outside waters reach gale force
35-40kt.

The next wave of fronts in the series will be approaching late
Monday night and looks to take a similar track as the first,
although with timing uncertainty in the models. Models do agree
however, that precip will back off ahead of this front late
tonight.

.LONG TERM.../Tuesday through Friday as of 4 PM Sunday/ A mean
trough with an associated surface low pressure centers itself
over the Gulf through the long term period. Through the period
multiple lows spin up in the gulf bringing consecutive waves of
precipitation, some more impressive then others. Tuesday, a
strengthening low swings up into the SE gulf bringing with it a
high end gale force front (winds 35-45 kt). This low will lift N
through the day before dissipating over the central panhandle.
This system looks to have decent warm air advection associated
with it, leading to surface temperatures to warm above freezing
across most of the panhandle. Across the south precipitation will
be rain, but across the north precip is expected to start as snow
before changing to rain. Current thinking is that snow
accumulations between 2-4 inches are possible across the far
north with lesser amounts through the north central.

Wednesday turns to more of a shower pattern before yet another
wave enhancement moves through the southern panhandle. This
enhancements looks to bring more rain as temperatures will still
be above freezing. By Wednesday evening, strong cold air
advection moves into the panhandle from the gulf putting SEAK
under a snow shower pattern once again. This time, temperatures
across the entire panhandle could fall below freezing, letting
everyone play in the snow late Wednesday night into Thursday.

Towards the end of the week, confidence drops significantly has
models struggle to place a new low in the gulf. The GFS/CAN have a
drying trend in place for the weekend while the EC brings in a
storm across the NE gulf. One area where agreement is better, is
on cooling 850mb temperatures through the weekend. Today, MOS back
off on such extreme cold temperatures for the weekend so decided
to follow suit and nudge temps back up slightly.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Strong Wind late tonight for AKZ027.
     Winter Weather Advisory from 2 PM this afternoon to 4 AM AKST
     Tuesday for AKZ020-025.
     Winter Weather Advisory from noon today to 11 PM AKST this
     evening for AKZ021-022.
     Winter Weather Advisory from 1 PM this afternoon to 11 PM AKST
     this evening for AKZ029.
MARINE...Gale Warning for PKZ036-042-043-051-052-310.
     Small Craft Advisory for PKZ012-022-041-053.

&&

Ferrin/CC

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