Heavy Snow in Alaska, December 26 to 27, 2021

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
225 PM AKST Sun Dec 26 2021

.SHORT TERM.../Through Monday night/ A fast moving system
dropping SE along the outer coast spreading snow across the entire
panhandle is the main weather story for the short range.
Currently only high clouds over the northern half of the panhandle
is the current effect from the incoming system, though Biorka
Island radar does show some precip possibly well offshore this
afternoon. Meanwhile outflow winds have been on a decreasing trend
(only Skagway is blowing with 15 to 20 kt winds) while
temperatures have shown a slow, if steady, warm up this afternoon
(many areas that were below zero over the last day to two have
warmed above zero, and temps in the teens are more wide spread
this afternoon).

This evening, clouds will continue to increase and lower, and
precip will begin from NW to SE across the panhandle as a piece of
the system that is battering the Alaskan Interior will move
through the area. Much of its moisture and dynamics will have been
lost to high terrain and transiting down the E side of the upper
ridge to our W, but enough remains that widespread snow is
expected tonight into early Monday. Expected accumulations remain
mostly unchanged from the previous forecast, however uncertainties
remain. The deep cold air still in place over the panhandle
presents one problem with snow ratios possibly reaching 15 or even
20 to 1. Meaning that the snow that falls will be dry, fluffy, and
may potentially accumulate quickly. Problem number two is the
deformation band that will develop over the central and southern
panhandle overnight. It is wavering first eastward and then
westward over the area and depending on how long it sticks over
a certain area may dump more snow in localized areas. Problem
three is the speed at which the system is moving through. It is
forecast to be out of the panhandle as soon as Monday morning so
that will put a limit on snow totals. At this point, advisory
level snow accumulations still look reasonable for the areas under
the advisory, with lesser amounts elsewhere. However, if any
areas get 6+ inches, it will most likely be around Juneau,
Petersburg, or Wrangell though the chance of it happening is
somewhat low at the moment. Also, The Haines and Skagway areas
will be watched as well as they present the best chance (though
somewhat low chance) for any non advisory areas to receive more
snow then forecast.

Into Monday and Monday night, the system quickly departs the
panhandle and skies start to clear out again. The cold air from
the weekend will have been pushed off to the east through so
temperatures and winds will not be as much of an issue as they
were over the weekend.

.LONG TERM.../Tuesday onward/ Two well-defined low-pressure
systems will bring widespread and organized precipitation to the
region midweek and again by the end of the week. Increasing
confidence that precipitation will be a mix along the outer coast
from the first system and the second system may bring moderate
snowfall.

The long-term period begins with partly cloudy to clear skies with
an isolated chance of flurries along the outer coast Tuesday
morning. As the first well-developed low moves into the Gulf on
Tuesday night, expect temperatures to increase by Wednesday late
morning resulting in most areas along the coast changing from snow
to a mix of precipitation and possibly straight rain. Total
snowfall amounts look to remain below the advisory level for the
outer coast and near or above advisory elsewhere, with the rain
on snow leading to a hazardous morning and/or evening commute
Wednesday. This system has increased in speed again, which means
clear skies are possible Tuesday evening and again Wednesday
evening, with the quick moving system in the middle. Thursday
looks to be another clear day, with clouds increasing overnight
into Friday as the next low approaches.

The second low follows in a similar path as the first one and
could bring moderate to heavy precipitation to the panhandle.
EURO and GFS Ensembles are giving 50-70% chance of greater than
0.50" of QPF over 24 hours and 20-30% of greater than 1.00" of QPF
over 24 hours. QPF amounts like that would mean significant
snowfall if temperatures end up being cold enough to support snow.

Inside marine winds were increased in the Northern Lynn Canal
region through the long term as a result of a tighter pressure
gradient and outside waters were moderated to below gale-force.
Overall forecast confidence is average with the timing of the
system below average due to changes 3-6 hour speed ups each day.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory from 9 PM this evening to 9 AM AKST
     Monday for AKZ023>028.
MARINE...Small Craft Advisory for PKZ022-041>043-051>053.

&&

EAL/KRT

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