Gale Warning 833, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
441 PM AKST Thu Dec 21 2023

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Tonight
through Sunday)...

A rather quiet day today for areas along the western Gulf and Cook
Inlet extending up into the Mat-Su Valleys. Kodiak and much of Kenai
Peninsula saw generally clear skies with fog and stratus mostly able
to mix out along the western Kenai and southern Cook Inlet. The
Anchorage Bowl managed to clear out briefly with temperatures
falling from the teens to near 10 degrees before stratus settled
back in helping to raise temperatures back up into the upper teens
and lower 20s. A few lingering showers ongoing across the eastern
Prince William Sound and Cordova eastward along the coast and light
snow in the Copper River Basin from a decaying low moving northward
into the Basin. Quiet weather will continue overnight into Friday
morning with transient shortwave ridging passing through.

The quiet weather will be short-lived, however, as a strong storm
system tracking south of the Aleutian Chain will move into the
southern Gulf of Alaska by tomorrow afternoon and evening. This
system will bring widespread storm and gale force winds and seas of
15 to 20 ft into the northern Gulf Friday night and into Saturday
morning as the associated frontal boundary lifts north across the
Gulf. Warm, moist air will be transported north with this system
allowing from modest precipitation amounts for Kodiak Island, the
eastern Kenai Peninsula, western Prince William Sound, and the
Southcentral coastal areas. The coastal mountains will also see
modest snowfall amounts with plenty of moisture to work with. Strong
easterly winds should allow for a decent downslope component
initially setting up for the eastern Kenai to the Anchorage Bowl and
up into the Mat-Su Valley. May see some light precipitation working
into these areas Saturday and Sunday as a shortwave rounding the
southern periphery of the parent low rapidly deepens and lifts
northwards towards western Prince William Sound.

Primary forecast challenges are focuses on precipitation type as warm
air is transported north. Many low-elevation coastal areas will
likely see precipitation start out as snow before transitioning to a
rain-snow mix or all rain. The higher elevations will see all snow
but will likely see snow elevations rise to about 1200-1500 ft.
While forecast confidence remains high through Friday, differences
in timing and position of the low as it moves into the northern Gulf
quickly erode forecast confidence by late Saturday into Sunday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA/ALEUTIANS/BERING SEA (Days
1 through 3: Tonight through Sunday morning)...

The overall forecast remains on track this evening. Numerical
guidance has slowed the track of an Aleutian low through the
weekend ever so slightly, but this should promote little change to
expected winds and snow across the Eastern Aleutians, AKPEN and
Greater Bristol Bay.

A strong occluded low is tracking south of the Central Aleutians
this evening. Its front is spreading across the Central Aleutians
and is expected to overspread the Eastern Aleutians and Alaska
Peninsula later tonight into Friday. Confidence remains high that
gale to storm force winds will accompany the front, along with
snow, blowing snow, and reduced visibility. Temperatures across
the Eastern Aleutians have been steadily warming through the day
today and temperatures in Unalaska have warmed into the mid 30s.
Thus, the threat for blowing snow will be delayed somewhat across
the Eastern Aleutians until temperatures begin to fall again
later tonight. Further east, easterly winds over the Alaska
Peninsula are expected to gradually back to a northeasterly
direction on Friday with sustained winds on the order of 40 to 50
mph and gusts approaching 60+ mph. Temperatures across the Alaska
Peninsula should stay cooler and below freezing. Increasing
snowfall across the region will support blowing snow and blizzard
conditions with visibility down to a quarter mile at times. Winds
are expected to be more subdued across Bristol Bay, but, along
the coast, blizzard conditions are also forecast with increasing
snow to fall within winds of 25 to 35 mph. From Saturday into
Saturday night snow totals from Manokotak to New Stuyahok will
range from 6 to 8 inches. Finally, with the low taking a more
southerly track, portions of Bristol Bay may be spared from
stronger winds. There will be a period, however, of easterly
winds spilling out of the Kamishak gap, which could promote
blizzard conditions on the southern side of Lake Iliamna late
tonight, before flow diminishes Saturday morning.

&&

.LONG TERM FORECAST (Days 4 through 7: Monday through Thursday)...

An elongated upper level low centered near Nunivak Island remains
through Wednesday before moving northeast. Multiple shortwaves
will rotate around the upper low through midweek. A low pressure
and associated fronts will produce areas of precipitation across
the central Aleutians and pushes into the southern AKPEN by Mon
night. The low and front continue across the gulf Tue afternoon.
Locally heavy precipitation is expected, with rain near the coast,
mixed precipitation inland, and snow towards the interior,
stretching from the southern Kenai peninsula to the Canadian
border. A second front continues similar conditions across
southcentral Tue night into Thu. Gusty winds are expected
throughout the forecast period over marine locations.

Unsettled conditions are expected over the Aleutian Chain through
Wed. Transient surface lows will bring local areas of gale force
winds across the eastern Aleutians Mon, with the more active
weather pushing south into the northern Pacific by Wed. A weak
north Pacific ridge moves over the Aleutians before flattening out
Thu. Conditions will remain showery over the Bering through the
end of the period as a northwest flow continues.

Eovino

&&

.AVIATION...

PANC...Cloud cover is generally expected to clear out this evening
in wake of a departing low. However, lingering low-level moisture
in the absence of cloud cover may result in low stratus and/or fog
developing once again overnight. Confidence is low if it'll affect
PANC directly, but high that patchy MVFR/IFR conditions will exist
in the area.

Winds will remain light throughout the period.

-Brown

&&