Winter Storm in Alaska, December 3 to 5, 2023

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
255 PM AKST Sun Dec 3 2023

.SHORT TERM.../through Monday night/...The parade of lows
continues. Tonight, the low currently in the gulf will move north
and fade out. As the low moves on, winds will decrease, waves will
decrease, and any leftover rains will diminish or lighten up.

But, the next gale force low will move in before we can really
feel the effects of the lull between lows.

The associated front with this low will track north, bringing the
panhandle preciptiation. While most areas will see rain or brief
snow before it switches to rain, the northerly winds in Northern
Lynn Canal are expected to keep the cooler air in place. So when
the precip collides with the cooler air, moderate to heavy snow
will result. A Winter Storm Warning has been issued ahead of this
next round of heavy snow for the northern Lynn Canal area.

Along with the snow in the north, the coast and parts of the
southern panhandle will see strong gusty winds as the front moves
through.Strongest gusts upwards of 40 to 55 mph are possible as
the front passes, before the gusts decrease to around 35 to 45
mph.

.LONG TERM.../Tuesday through Sunday/...Beginning the Tuesday
time frame, the system discussed in the short term will be moving
into the northern gulf. After settling near Prince William Sound,
it will become stationary and remain through most of the week,
slowly decaying. The result is a relatively consistent pattern for
the rest of the week with constant onshore flow and periods of
rain and snow. The initial two waves will be coming to a close on
Tuesday with snow for the highways and rain elsewhere. Main area
of concern for the second wave is the Klondike highway due to
higher elevation and how far the moisture will push up through the
channels. Current thinking is that Haines will properly turn to
rain in the morning hours from rain and snow with the southerly
push up Lynn Canal. Skagway will likely change soon after,
however, the Klondike highway will likely stay snow through the
day as the warm air attempts to work itself northward.

Beyond Tuesday is more uncertain. While there is constantly onshore
flow, there are some indications in both deterministic runs and
ensemble runs that some shortwaves will push up along the decaying
low in the north central gulf. Such lows will likely bring slightly
enhanced winds and precip relative to the 15-20 knot winds and light
rain. Significant snow accumulation (greater than one inch) is not
currently on the agenda for the rest of the week, although it is
possible to see some mixed precipitation and snow later in the week.

Finally, some indications of a potent system moving up from the
south during the weekend timeframe. While details are still being
ironed out, some increased winds and possibly snow may be in SE AK's
future.

&&

.AVIATION...IFR/MVFR conditions lifted to MVFR Sunday, as showers
moved ashore under a weakening front. A few isolated
thunderstorms popped up in the southern Panhandle. More precip,
increasing surface winds, and LLWS moves in Sunday night under a
gale force low. MVFR, dropping to IFR at times for the majority of
the Panhandle, with IFR more likely in the far north of Lynn
canal from falling snow while warming temps will result in other
areas receiving mostly rain. Unfavorable flight conditions
continue into late Tuesday at least.

&&

.MARINE...The wind and waves over the marine waters are expected
to diminish through the evening and into the overnight as the
current low in the gulf fades out. So the wave heights out there
now, upwards of 10 to 20 feet in the gulf, should diminish to
around 10 to 15 by late tonight. And the wind speed around 15 to
30 kts should decrease to around 15 to 20 kts by late tonight.

The inner channels are currently seeing speeds around 10 to 20 kts,
with some isolated areas seeing lighter speeds and other areas,
mostly around Icy Strait, seeing speeds upwards of 20 to 30 knots.
Decreasing speeds are also expected for the inner channels
tonight, to around 10 to 15 kts.

All that being said, the next gale force low will move into the
gulf tomorrow. So all those diminishing winds and waves will go
right back up as the low approaches. As the front moves through,
wind speeds upwards of 30 to 40 kts are expected along the front
in the gulf. Waves will also reach near 20 feet along the front.

Inner channel wind speeds will increase to around 20 to 25 kts as
the front tracks north. Speeds in the southern inner channel
waters will be a little higher, at up to 35 kts.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Storm Warning from noon Monday to noon AKST Tuesday for
     AKZ318-319.
     Strong Wind from Monday morning through Monday afternoon for
     AKZ323-328-330.
MARINE...Gale Warning for PKZ036-641>644-661>664-671-672.
     Small Craft Advisory for PKZ012-013-021-022-032>035-053-651-652.

&&

SHORT TERM...GJS
LONG TERM....NC
AVIATION...PRB
MARINE...GJS

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