Winter Storm in Alaska, December 29 to 30, 2023

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
640 AM AKST Fri Dec 29 2023

.SHORT TERM...The active weather continues unabated across the
panhandle as still more rain and snow arrive through the duration
of the week and into the weekend.

The low SW of Haida Gwaii which has been sending waves into the
panhandle for the past few days is finally moving northward. The
system will arrive in the Gulf of AK as a decaying gale force low
on Friday, before ultimately moving onshore Saturday. Although on
a weakening trend, the low will bring with it a respectable amount
of moisture, and river rises are possible for some locations. The
winds associated with this system across land will not be as
impressive as with some previous systems, but still think that the
southern panhandle could experience a period of strong winds this
morning. Small craft winds are expected for parts of the inner
channels, alongside some gale force winds for the outer coastal
waters.

Although the precipitation will primarily fall as rain or a rain
snow mix across most of the panhandle, one significant exception
will be far northern locations. The warm air advection surge
moving N will likely stall in Lynn Canal, where northerly winds
will help keep the warming temperatures at bay through much of
Friday. This will be especially impactful for areas of elevation
along the Haines and Klondike Highways. Winter Storm Warnings have
been issued for these areas from 9 AM Friday to 9 AM Saturday,
with total accumulations of up to 12 inches possible - especially
closer to the border. Significantly lower snow totals are expected
for the towns of Haines and Skagway at sea level, where the warm
air will ultimately manage to advect into the area Friday or
Friday night. At the time, significant uncertainty still exists
with these snow totals - a quicker warm air surge would result in
an earlier changeover to rain and substantially lower snow totals
for the highways.

.LONG TERM.../Saturday through Thursday/...The decaying low in
gulf will continue to bring unsettled weather for the start of
Saturday. This low will continue to support warming temperatures
across the region for the start of the weekend along with rising
850mb temperatures. With the warmer temperatures, expect all the
precipitation to remain as rain during this time with the
exception of places at altitude and along the very far northern
panhandle. Most of the heaviest precipitation looks to be limited
to the mountains at this time.

After this warm up, ensemble guidance continues to struggle with the
mid range pattern as a low over the Bering Sea will continue to
dictate flow from upstream. This longwave trough will pull colder
air down from the arctic and allow for some moderating and cooling
of temperatures aloft. With this cooling, precip type is expected to
switch to more of a mix of rain and snow or straight if any moisture
does fall across the area. Heading into the middle of next week,
ensemble guidance wants to bring a shortwave trough through the area
before trying to build a ridge into the area.

&&

.AVIATION...Wide range of conditions across Southeast Alaska today
varying from VFR conditions to Low IFR conditions (for both CIGs
and VSBY) Little change expected over the next 24 hours. LLWS
intensifies during the period as well with the next weather system
tracking north over the eastern Gulf of Alaska. LLWS will be
strongest over the southern Panhandle this morning, diminishing
slightly as the core of the strongest winds moves north,
eventually reaching the northeast Gulf Coast by Saturday morning.
Think the far northern inner channels will be spared the LLWS, but
will have to contend with low CIGs/VSBY in snow.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Storm Warning until 9 AM AKST Saturday for AKZ318-319.
MARINE...Gale Warning for PKZ641>644-661>664.
     Small Craft Advisory for PKZ022-033-035-036-651-652-671-672.

&&

SHORT TERM...GFS
LONG TERM....SF
AVIATION...Fritsch

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