Winter Storm in Alaska, December 25 to 26, 2022

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
645 AM AKST Sun Dec 25 2022

.SHORT TERM...Southeast Alaska continues to be at the forefront of
the active weather pattern, with more accumulating snow possible,
in particular Sunday afternoon and evening as favorable jet
dynamics over the Pacific continue to bring in system after
system. Radar and infrared satellite imagery as of the time of
writing indicate that organized precipitation connected to the
previous system has largely ended over the panhandle, though some
freezing rain, rain and snow showers remain across the area.

These showers will prove to be the harbinger of the next system - a
storm force front which has begun advancing into the panhandle and
which will impact the area through Monday. The low itself will
remain well offshore, centering itself in the western central
Gulf of Alaska. Operational guidance is progging that the system
will deepen to as low as 947 mb per 00z GFS and Euro model runs.
The system is being supported aloft by a powerhouse jet - one
which per models will reach 180+ kt aloft at 300 mb through parts
of Sunday and Monday. In the low to mid levels, respectable
amounts of integrated moisture transport will combine with a
strong surge of warm air advection associated with the system,
with 850 mb temperatures rallying significantly in the immediate
wake of the low's frontal band. All of these will add up to
produce a powerhouse storm - with the primary silver lining for SE
AK being that the worst effects will be lessened by the distance
between the low and SE AK proper.

As the frontal band enters SE AK proper, expect the S half of the
area to be favored for rain, as previous systems will have helped
push 850 mb temperatures to -3C or warmer across much of the area,
and strong WAA aloft will see any remaining pockets of cooler air in
this part of the panhandle quickly mixed out. Heavier rain over
the S panhandle could result in some snow melting, with some
ponding and river rises possible. A high wind warning has also
been issued for Prince of Wales Island which will last through
much of the afternoon The situation is more tricky for the N half
of the panhandle and Angoon where colder air remains more
entrenched and which will favor accumulating snow. The heaviest
snowfall will occur during the late afternoon and evening hours on
Sunday, with winter weather advisories in place across the N
panhandle and much of the Icy Strait Corridor, including Juneau.
At this time, it looks like 3 to 5 inches of snow are favored
around the Icy Strait Corridor, with slightly more (4 to 6 inches)
in Skagway and Haines and along the Klondike Highway. It is
possible that some isolated locations may see higher totals,
particularly if particularly favorable snowfall ratios develop in
conjunction with the surge of moisture from the front. Strong
winds will also be present in some locations, and blowing snow is
also anticipated as a result, which will likely result in drifting
and reduced visibilities for some parts of the area.

One area of concern will be the conjunction of high tides with the
advancing system on Sunday. The possibility does exist for some
minor coastal flooding along parts of Baranof island and outer
coastal islands along the Prince of Wales area, and a coastal
flood advisory has been issued for these areas.

Beyond this stage, a weaker gale force system moves into the
panhandle on Monday, providing additional moisture and bringing
more precip back into the area in conjunction with the remnants of
the previous front. More snow is possible for the N half of the
SE AK with this system. For further details, please see the long
range forecast.

.LONG TERM.../Monday through Thursday Night/...The frontal system
will continue to weaken and move away from the Panhandle on
Monday, decreasing winds over the eastern Gulf from around 40 kt
Gale to around Small Craft through Monday evening and winds over
the Inner Channel marine zones decreasing from up to 30 knots
early Monday morning to around 20 knots by the evening. Precipitation
rates and chances will also decrease from south to north over
that same timeframe.

We will have a break between systems on Tuesday with only chances
slight chance to chances of light precipitation and relatively
benign winds for southeast Alaska Winter standards.

Another frontal system approaches the area from the southwest for
Wednesday through Thursday with increased chances for only lighter
precipitation and winds increased from small craft to Gale for the
Outside Waters from Wednesday through Thursday via a tightening
pressure gradient between the frontal system and relatively
higher pressure over northwest Canada. Inner Channel marine winds
look to increase up to low end Small Craft magnitudes starting
early Thursday morning and lasting through the period.

As for temperatures, the milder weather for this time of year
looks to stay around the Panhandle through the period. Highs look
to reach into the low to mid 40s for the southern Panhandle and
into the low to mid 30s for the northern Panhandle. Overnight
lows look to dip into the upper 20s for the northern Panhandle and
into the mid to upper 30s for the southern Panhandle. There as a
steady and gradual cooling trend as we progress through the long
term forecast period. Elevated model forecast 850 mb temperature
advection, weakening through the period, backs this trend
conclusion.

As of this morning, operational weather forecast models were in
good agreement and ensemble member spread was relatively narrow
for this time of year. Therefore, forecast confidence is above
average.

&&

.AVIATION...The front moving into the region from the south will
cause SE LLWS from PASI southward between 1-2kft increasing to
50-60kt through the mid morning. Heavy rain expected across the
south with conditions to MVFR. Over the central areas, light
freezing drizzle has formed a glaze in some areas, including
Juneau. The front will move into the central panhandle with mainly
rain for PAPG region while Icy Strait to PAJN northward will see
mainly snow developing through the day with conditions lowering to
MVFR/IFR.

&&

.MARINE...Gale force and small craft winds remain across much of
the area through Sunday, with storm force winds in the Gulf and
some of the outer coastal waters. Some amelioration in wind speeds
anticipated late on Monday. Wind directions in the N inner
channels could be more variable than forecast at times as the
advancing storm force frontal band interacts with still strong N
outflow winds.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Strong Wind from 9 AM AKST this morning through this afternoon
     for AKZ317.
     Strong Wind late tonight for AKZ317.
     Strong Wind until noon AKST today for AKZ318.
     Winter Weather Advisory from noon today to 3 AM AKST Monday for
     AKZ318-319.
     Strong Wind until 6 AM AKST early this morning for AKZ319-330-
     332.
     Winter Weather Advisory from noon today to 9 PM AKST this
     evening for AKZ320-321-325.
     Strong Wind through late tonight for AKZ323.
     Coastal Flood Advisory from noon today to 4 PM AKST this
     afternoon for AKZ323-327-328.
     Coastal Flood Advisory from 11 AM to noon AKST Monday for AKZ323-
     327-328.
     Strong Wind from 9 AM AKST this morning through this evening for
     AKZ325.
     Strong Wind from noon AKST today through this afternoon for
     AKZ326.
     Strong Wind from 3 PM AKST this afternoon through this evening
     for AKZ327.
     Strong Wind until 7 AM AKST this morning for AKZ328.
     Strong Wind from 3 PM AKST this afternoon through this afternoon
     for AKZ328.
     High Wind Warning until 3 PM AKST this afternoon for AKZ328.
     Strong Wind from noon today to 3 PM AKST this afternoon for
     AKZ329.
     Strong Wind from 9 AM AKST this morning through this evening for
     AKZ330.
     Winter Storm Warning until 6 AM AKST early this morning for
     AKZ331.
MARINE...Storm Warning for PKZ041>043-051-052.
     Gale Warning for PKZ012-013-022-033>036-053.
     Small Craft Advisory for PKZ011-021-031-032.

&&

SHORT TERM...GFS
LONG TERM....JLC
AVIATION...Ferrin

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