Heavy Snow in Alaska, December 2 to 3, 2021

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
303 PM AKST Thu Dec 2 2021

.SHORT TERM.../Through Fri night/ Onshore flow and snow showers
are the rule of the day across the panhandle. A persistent low in
the northern gulf is the main culprit of this. Snow has been
observed all the way down to the southern panhandle today and snow
amounts have varied widely ranging from around 1 inch to 6 to 9
inches at Yakutat and Sitka. This has been mostly due to snow
showers concentrating on one area and missing others. Sitka ended
up being upgraded to a winter storm warning from an advisory as
heavier showers traveled over them today.

The onshore flow and snow showers will continue to be the main
forecast challenge through the next 36 hours. The main thing that
will gradually change this pattern is the northern gulf low will
drift to the SE through the period, gradually shutting off the
showers from NW to SE. Yakutat will likely mostly shut off
overnight tonight, the northern panhandle will be toward tomorrow
morning, and the south will likely still see some snow showers
into Fri night. Expected snow amounts will continue to be widely
varied as showers train over some areas but miss others. Winter
weather advisories remain up for the Petersburg, Wrangell and
Hyder areas through Fri morning, and a winter storm warming
remains up for Sitka through 9 pm tonight.

Winds compared to yesterday are not that much of a concern. South
winds of around 15 to 25 kt remain the norm in the inner channels
this afternoon, though the northern inner channels are expected to
flip to a northerly early this evening as high pressure builds in
the Yukon. Highest winds will be in the southern gulf on the
south side of the weak low as it slides SE (up to 30 kt westerly),
and in Lynn Canal due to northerly outflow through Fri night (up
to 30 northerly). Skagway may have enough cold air coming down
from Canada that gusts up to 40 mph may be observed Fri afternoon
into Fri night as well. Other areas will mainly be 20 kt or less
for the most part.

Main forecast changes were for local effects for winds and trying
to pin down where the highest snow accumulations will be from the
snow showers.

.LONG TERM.../Saturday through Tuesday night/...The mid-range
starts with a trough exiting to the southeast with more onshore
flow in its wake. The risk of snow showers continues through the
weekend, better chance for the north on Saturday and the south on
Sunday. It will be plenty cold throughout the atmospheric column
to support snow across the panhandle, so those areas that do
experience one or more showers could pick up a few inches of snow.
Amounts and rates will be variable due to the showery nature, but
generally look to remain below advisory criteria. Temperatures
were nudged downward for northern Lynn Canal on Saturday as cold
air from the Yukon makes its way across the border with northerly
flow.

The next low pressure system tracks along the AK peninsula to near
Prince William Sound by late Monday night. This will push a front
towards the panhandle Monday for Yakutat into Tuesday for the rest
of the panhandle. Flow is expected to turn southwesterly as the
front approaches, which brings the rain/snow line into play once
again. 850mb temps and 1000-850mb thickness values suggest that
the central and northern panhandle will start as a period of snow
with the rain/snow line getting as far north as the Icy Strait
corridor by Tuesday morning. This will need to be watched because
given the cold air in place, warning or advisory level snowfall
may occur before mixing with rain - specifically for Yakutat,
Juneau, and the Icy Strait corridor. Forecast winds were increased
and the timing adjusted with the arrival of the front, but
remained small craft strength for now.

Forecast confidence for the weekend is below average as is typical
in a showery pattern, especially regarding the snow amount and
location details. Confidence in the overall pattern evolution
regarding the front arrival early next week is above average.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory until 6 AM AKST Friday for AKZ026.
     Winter Weather Advisory until 3 PM AKST this afternoon for
     AKZ017-020-022-025.
     Winter Storm Warning until 6 PM AKST this evening for AKZ023.
     Strong Wind Friday afternoon for AKZ018.
     Winter Weather Advisory until 6 PM AKST Friday for AKZ029.
MARINE...Small Craft Advisory for PKZ012-022-033-035-041>043-051>053.

&&

EAL/BFL

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE JUNEAU AK
1021 AM AKST THU DEC 2 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0800 AM     HEAVY SNOW       1 E YAKUTAT             59.55N 139.71W
12/02/2021  M8.0 INCH        YAKUTAT            AK   TRAINED SPOTTER

            A TRAINED WEATHER SPOTTER REPORTED 8 INCHES
            OF NEW SNOW HAS FALLEN SINCE SHORTLY AFTER
            SUNSET. SNOWFALL RATES HAVE DIMINISHED AND
            IT IS CURRENTLY LIGHTLY SNOWING.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE JUNEAU AK
1129 AM AKST THU DEC 2 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1028 AM     HEAVY SNOW       3 NW SITKA              57.09N 135.39W
12/02/2021  M5.8 INCH        SITKA              AK   TRAINED SPOTTER

            3 -6 INCHES REPORTED ACROSS SITKA THURSDAY
            MORNING, WITH LOW VISIBILITY AROUND 9:30AM.

&&

KRT