Gale Warning 786, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
515 AM AKST Tue Dec 5 2023

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

A gale force low in the Southern Gulf of Alaska will continue to
slowly drudge northward today, tonight and Wednesday with the
latest ECMWF, Canadian and NAM model consensus of a 983 mb low
tracking slowly north to be located around 45 nm southeast of
Middleton Island Wednesday morning. The GFS has a low of similar
strength but tracking further to the west and slower than the
other models. Model tracks become more divergent into Thursday
with the ECMWF, Canadian and NAM consensus track moving the low into
the Copper River Delta to the east of Cordova Wednesday evening
while the GFS tracks the low northwest into the Eastern Kenai
Peninsula and Western Prince William Sound and dissipating
Thursday afternoon. Based upon current low track and model
performance we preferred the faster, slightly weaker and further
east track of the ECMWF, Canadian, and NAM as well as sever other
high resolution models over the GFS which seems to be an outlier
solution at this point.

The faster, weaker and further east track will manifest itself
with a shorter initial precipitation period, with lesser snowfall
totals especially on the western edge of the storm over Cook
Inlet, the Western Kenai Peninsula, Anchorage and the MatSu
valley with the first round of snow as the low moves north and
makes landfall along the coast near the Copper River Delta, but
may produce more snow on the back side of the low as it moves
north into the Copper River Basin and cold west to northwest flow
produces upslope flow along the Chugach Front Range over the
Western Kenai Peninsula, the Anchorage Hillside and Eagle River as
well as the Talkeetna Mountains and the MatSu valleys. Snowfall
totals through Wednesday afternoon range from 1 to 6 inches
depending on the track of the storm. Higher amounts will be
possible in the southern Copper River Basin & Thompson Pass, where
more moisture is wrung out over the coastal mountains. Blowing
snow is expected to be an additional hazard for Thompson Pass as
cold air continues to filter out through gaps, leading to
continued sustained winds of 40 to 50 mph. Small changes in the
track of this storm will produce large differences in the timing,
and location of the heaviest snowfall.

By Wednesday, the low moves into the northeastern Gulf, drawing
cold air across the Western Alaska Range. This cold air advection
is likely to enhance gap winds in the western Gulf to storm
force, with gusts in excess of 65 knots (75 mph). Precipitation
will begin to diminish Wednesday evening in Prince William Sound
and surrounding mountains, but upslope snow showers will likely
linger along the Front Range of the Chugach and Talkeetna
mountains including the Anchorage area and the MatSu Valleys into
Thursday as a broad low with a strong upper-level component tracks
into Western Alaska. Its cold front brings potential for another
round of snow to Southcentral as it sweeps eastward out over the
Gulf.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA AND BERING SEA/ALEUTIANS
(Days 1 through 3)...

Key Messages:

-Elevated sustained winds and wind gusts expected across much of
 SW Alaska & the Bering through Wednesday afternoon, with gusts up
 to 65mph possible along the Alaska Peninsula.

-A developing Kamchatka low will bring increased precipitation
 chances to SW AK through the central Aleutians by tomorrow
 night.

Discussion:

No major changes to the forecast at this time as much of the AOR
currently remains under mostly zonal flow with weak ridging aloft.
In tandem with a low pressure within the GoA, anticipating
another day of elevated & gusty winds to traverse across the
Alaska Peninsula, with sustained winds around 40mph and isolated
gusts up to 60-65mph possible through gap-wind areas like King
Cove, Sand Point and Chignik. Good news, these winds will slowly
weaken through Wednesday afternoon as the pressure & temperature
gradient relaxes with the Gulf low opening & sliding eastward
towards Prince William Sound.

Out west over the Bering, expecting cooler temperatures and
intermittent snow showers to persist through the forecast period under
predominate W/NW-ly flow, aided by a developing and compact
Kamchatka low. This Kamchatka low will gradually deepen and shift
SE towards St. Lawrence Island through Wednesday and eventually
over mainland AK by Thursday. This low will send another shot of
reinforcing cold air and lead to heavier snow/snow showers for
the Bering and western coastlines of the Mainland and AKPen to
round out the short term forecast.

&&

.LONG TERM FORECAST (Days 4 through 7)...Friday through Monday...

The longwave trough over the eastern Bering and western Alaska,
meanders and drifts southeastward into the Gulf of Alaska with a
surface low heading toward the eastern Gulf of Alaska. There is
low confidence for the weekend period with the location of the
surface and where the heaviest precipitation will be, but
expecting an active pattern ahead for eastern Alaska. High
pressure ridging continues indicate amplification for the western
Bering Sea that encourages cool, northerly flow across the Bering
Sea. Snow showers can be expected under the northerly flow,
especially for the central and east Bering. A closed low forms
over Southern Mainland, and drifts to the East through the
weekend.

A North Pacific low with more available moisture and winds
approaching gale force will lift northward toward the Aleutians,
but looks to drift east toward the Gulf before reaching the
Islands. Bands of precipitation would still be reinforced and
would like keep precipitation going, locally heavier at time along
the Aleutians. Another surface low appears to develop and south
of the Alaska Peninsula and tracks into the western Gulf. At this
time, potentially heavy precipitation (10 percent exceedance of 2
inches in 24 hours) to the northern Gulf coast early next week is
possible. There is still low confidence with the position of the
low this far out in time, but is a feature worth tracking over the
next few days.

rux

&&

.AVIATION...

PANC...Mostly VFR conditions through this afternoon, although
cloud ceilings at or below 5000' are expected to continue this
morning. A wintry mix will continue this morning followed by a
brief break in the afternoon. Later this evening, snow chances
return and conditions will drop to MVFR or lower at times.

&&