High Wind in Alaska, December 27, 2023

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
704 AM AKST Wed Dec 27 2023

.SHORT TERM...Active weather returns to the panhandle as another
system begins moving northward, bringing with it rain, freezing
rain, snow, and windy conditions through the next few days.

A front associated with a low currently located SW of Haida Gwaii
as of the time of writing has begun advancing into the panhandle,
with cloud cover already on the increase across the area. As this
front continues to move north, anticipate that a period of
freezing rain may be possible for some locations in the S half of
the panhandle - though am not anticipating any significant ice
accumulations. Any areas which do experience freezing rain will
switch over to rain through the daytime hours as warm air
advection slowly works its way N.

As the system continues to advance N, it will encounter cooler air,
setting the stage for a minor overrunning snow event. At this time,
am expecting only minor snow accumulations across the N half of the
panhandle, as drier air will help to inhibit the less than
spectacular moisture profile associated with said system. Another
band of precipitation will arrive during the overnight time frame,
and although this one will be more well-organized, am not
anticipating any noteworthy precipitation totals from it at this
time.

The tightening pressure gradient will lead to windy conditions -
including in places like downtown Juneau, where a mountain wave
event will develop Wednesday. At this time, there is a distinct
lack of truly substantial arctic air in place, but given the
considerable CBF and the likely development of an inversion,
strong wind are anticipated for Juneau. There is the potential
that winds for downtown Juneau may go above current forecast
guidance - and this will need to be monitored closely. Otherwise,
strong winds are anticipated in places like Skagway, and
widespread gale force and small craft conditions are expected
across the maritime waters.

.LONG TERM...
Main points in the long term:
-Rain, Snow continue Thursday.
-Moderate to heavy precipitation Friday into Saturday, with snow
 levels rising well above sea level.
-Warm temperatures continue across the Panhandle; 10F+ above
 seasonal normal.
-Quiet weather expected Sunday.
-Next disturbance moves in Monday or Tuesday.

Thursday morning rain snow continue as a shortwave trough carries a
surface low through the Panhandle but elevated winds along our
western shores. As this wave moves north Thursday, a longwave
trough will be moving across the Pacific towards the western
seaboard, with a decaying surface low lifting into the Gulf. As
this low moves near the coast it will begin to steer an
atmospheric river into the Panhandle, with isentropic analysis
indicating widespread heavy precipitation, especially in the
south. Warm air will accompany this system, with 850mb
temperatures well above their -4C mean. In response to this
vigorous trough of warm air aloft, expect snow levels to raise
above 5,000ft in the south, with 2000-3000ft snow levels in the
north, along with surface temperatures remaining 10F above their
seasonal normal. There is a high probability that southern Prince
of Wales sees afternoon temperatures reach the upper 40s, perhaps
even the low 50s again, by Friday afternoon. With this warming,
have decreased QPF slightly early Friday before the lower boundary
layer fully saturates later Friday afternoon.

Moderate to heavy rain, with warm temperatures, persists into
Saturday before cooler air settles in by Sunday, with widespread
precipitation and winds diminishing. Sunday into early Monday look to
be the quietest weather we’ve seen from the previous storm
cycles, with cluster analysis highlighting uncertainty with a
surface low amplifying south of the Aleutian Islands sometime
Monday, bringing in enhanced southerly swell and gale force winds
back to the Gulf.

&&

.AVIATION.../Until 12Z Thursday/...CIG and VIS conditions will
deteriorate through the period to primarily within the MVFR
category from approximately just to the north of the Icy Strait
corridor, southward, due to an approaching Gale-force frontal
system entering the eastern Gulf from the south. A mixture of
liquid and frozen precipitation looks to occur over portions of
the region during the TAF period, contributing to lowered VIS.
The tightened pressure gradient between the aforementioned weather
system and an area of high pressure centered over the Canadian
Yukon region will cause gusty SFC winds for the vast majority of
the Panhandle with likely mountain wave activity around the Juneau
area as the system continues to march northward and gradually
weakens. LLWS magnitudes peaking out at up to around 50kt look to
occur centered at around 2 kft out of a northeasterly to
southeasterly direction as the frontal system approaches and moves
in.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Strong Wind from 3 PM AKST this afternoon through this evening
     for AKZ318.
     Strong Wind through late tonight for AKZ325.
MARINE...Gale Warning for PKZ012-013-022-031-032-641>644-651-661>664.
     Small Craft Advisory for PKZ011-021-033>036-053-652-671-672.

&&

SHORT TERM...GFS
LONG TERM....AP
AVIATION...JLC

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