Heavy Snow in Alaska, November 20 to 21, 2021

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
435 PM AKST Fri Nov 19 2021

.SHORT TERM.../Through Saturday/ A low passes through the
southern panhandle bringing a mix of rain and snow this afternoon.
Through the evening, precipitation diminishes before the next
storm moves into the gulf early Saturday morning. Except for the
farthest southern areas, temperatures are below or near freezing
across the majority of the panhandle. Through tonight,
temperatures continue to fall priming the panhandle for snowfall
Saturday. This system will bring abundant moisture into the
panhandle. With temperatures below freezing ahead of the storm, a
change from snow to rain is expected as the front moves up the
panhandle. For this afternoon's update, several winter weather
products have been issued. A winter storm advisory is in effect
for cities including, Petersburg, Wrangell, Kake, and Angoon from
Saturday afternoon through Saturday evening. Also, winter storm
warnings are in effect for cities including Juneau, Gustavus,
Hoonah, and Elfin Cove from noon Saturday until early Sunday
morning. Then finally, a winter storm warning is in effect for
cities including Yakutat, Haines, and Skagway from Saturday
afternoon through Sunday morning.

The main impacts with this system will be widespread heavy snow
falling over a short period of time followed by rain on top of
snow. A potential significant impact from this system is the
possibility of a period of freezing rain late Saturday night
through early Sunday morning. As the occluded front pushes
northward through the Panhandle Saturday night, dry air will
filter in aloft from the south. This is an interesting set up as
the main low is near Kodiak Island with the front extending all
the way to SE AK. A dry slot behind the occluded front will push
in aloft Saturday night shutting off the heavy precipitation for
much of the Panhandle. Due to the dry air advection, the Dendritic
Growth Zone will become unsaturated while the lowest levels of
the atmosphere remain saturated. Since the warmer, drier air will
be overrunning the cold air at the surface, there will be a period
of time precipitation will be falling as rain while the surface
remains below freezing, especially across the Icy Strait Corridor.
Expect heavy snow to transition to light freezing rain overnight
before a transition to plain rain during the day Sunday.
Confidence remains low in the amount of freezing rain that could
fall; however impacts could be significant no matter what.
Expecting widespread heavy snow accumulations across the northern
2/3 of the Panhandle Saturday evening before a transition to light
freezing rain overnight.

.LONG TERM.../Sunday through Wednesday/ An active period
continues as a wintertime pattern remain around Southeast Alaska.

The period begins with an ongoing winter storm across Southeast
Alaska. By Sunday morning, A low will be pushing into the
Northern Gulf Coast near Cape Suckling with an occluded front
extending eastward toward the Panhandle. The triple point will be
located just offshore of Prince of Wales Island which, will be
the focus for wave development Sunday night. As mentioned in the
short term AFD, a dry slot will be pushing northward behind the
occluded front into the Panhandle Sunday morning. Expecting a
warming trend through the day, so P-type should transition to all
rain for most areas, except Upper Lynn Canal. Rain should be
fairly light Sunday with possible breaks in the clouds as the dry
slot remains over the region. Rainfall will increase in coverage
and intensity Sunday afternoon across the Southern Panhandle as a
wave develops along the front and moves north. Total rainfall
across the Southern Panhandle from the weekend into Monday could
be as high as 4 inches in Misty Fjords and around Ketchikan.
Heaviest rain should taper off and transition to showers Monday
morning as the wave moves off into Canada.

A relatively benign weather period sets up Monday through Tuesday
across the region as a low remains in the northern gulf and cold
air advection moves in aloft. Showers will persist during this
period transitioning to snow showers Monday evening through
Tuesday as colder air filters. The potential is there for minor
snow accumulations from snow showers, however exact locations and
amounts will become clearer over the next few days.

The active weather pattern picks back up again Wednesday and
continues through the end of the Holiday week. Multiple systems
are expecting to move north into the gulf and impact Southeast
Alaska during this time. Models and ensembles are hinting at a
storm system on Wednesday which has the potential to bring more
accumulating snow at sea level to the area. A much stronger and
potentially warmer system could affect the area for the
Thanksgiving timeframe. It's too early to go into the exact
details of these systems due to model discrepancies; however
confidence remains high that impactful weather will be present the
latter half of next week.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory from 9 AM to 9 PM AKST Saturday for
     AKZ024-026.
     Winter Storm Warning from noon Saturday to 3 AM AKST Sunday for
     AKZ020>022-025.
     Strong Wind Saturday afternoon for AKZ022-023.
     Winter Storm Warning from 3 PM Saturday to 6 AM AKST Sunday for
     AKZ017>019.
     Wind Chill Advisory from midnight tonight to 9 AM AKST Saturday
     for AKZ018.
MARINE...Gale Warning for PKZ012-013-022-036-041>043-051-052-310.
     Small Craft Advisory for PKZ011-021-031>035-053.

&&

CC/CM

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