Gale Warning 720, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
523 AM AKST Tue Nov 21 2023

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

The strong winds that several areas in Southcentral experienced
yesterday, such as the Matanuska Valley, northern Copper Basin, and
inlets around Prince William Sound have mostly diminished as of
early this morning. The exception is Thompson Pass where gusty winds
are likely to continue through at least mid-morning. High pressure
has shifted north over the northern half of the state as low
pressure system rotates up into the northern Gulf. Modest mixing of
the boundary layer yesterday and an increase in cloud cover from the
incoming upper low has allowed for much warmer temperatures across
Southcentral this morning. It also introduced quite a bit of dry air
to the surface and the column has been slowly trying to saturate.
The 12Z soundings at PAFC and PADQ compared to the the previous 00Z
soundings do a nice job of showing the column trying to saturate
along the Cook Inlet. As such, the bulk of the precipitation so far
with this incoming system has been confined to the north-central
Gulf with some lighter precipitation starting to move into the
Prince William Sound. Temperatures in Cordova are currently in the
mid 30s with light rain while both Whittier and Valdez hanging out
in the upper 20s with a wintry mix of freezing drizzle, light
freezing rain, and light snow having been reported over the past
several hours. Precipitation type will continue to be the biggest
forecast challenge over the next few days.

Models have come in much better agreement with the Gulf low rapidly
weakening today before moving inland near the Copper River Delta.
This will keep much of the precipitation confined to the coastal
areas east of Cordova today with light precipitation extending into
the Prince William Sound. There is a chance for a weak band of light
snow to develop over the Mat-SU Valley and down into the Anchorage
Bowl late tonight with a shortwave trough moving through. If we do
manage to squeeze out any precipitation, temperatures will be cold
enough to keep it all snow and only minor accumulations are expected.

By midweek, we will be keeping an eye on a large upper low moving
out of the North Pacific towards the Central Aleutians. The
associated frontal boundary will lift northwards towards Kodiak
Island by late Wednesday. This system will bring warmer air
northward helping to moderate temperatures, but it will also bring a
swath of precipitation north towards the Kenai Peninsula and
northern Gulf. Precipitation type will continue to be the forecast
challenge as the warmer airmass starts to work inland.

-PP

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: today
through Thursday)...

Clouds and areas of patchy fog/low stratus have filtered into
parts Southwest Alaska overnight. Conditions are expected to
remain dry today, but that will change on Wednesday with an
incoming front. Precipitation will move in from south to north,
starting initially as snow and transitioning to rain. There is
still some uncertainty for freezing rain chances during the
transition, but the trend is favoring a large area of freezing
rain in the Kuskokwim Delta and portions of the lower Kuskokwim
Valley. Bristol Bay and the Kuskokwim Delta coast may see a brief
period of freezing rain as well but the transition should be
quick enough for it to be very brief. Elevated winds across
Bristol Bay may lead to periods of blowing snow and some
visibility reductions, however, the snow is expected to be
heavy/wet, thus, significant blowing snow impacts are not
currently expected. This will continue to be monitored for any
changes.

The parent low of the aforementioned front scoots south of the
Aleutians over the next few days. Overall, impacts along the
Bering Sea and Aleutians are not expected to be abnormal. Gale
force winds will be prominent along both front, the first tracking
over the Western/Central Aleutians today, the second moving over
the Eastern Aleutians/Southern Alaska Peninsula tonight and
tomorrow. Precipitation will be mostly rain except for the along
the mountain tops where a rain/snow mix or all snow is expected.

KM

&&

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

The low sitting near the central and eastern Aleutians midweek
will begin to slowly trek east and weaken with its front pushing
through Southcentral under southerly flow. Warmer air and multiple
waves of precipitation can be expected through the end of the
week into next week. Temperatures will trend warmer, with Friday
being into the 40s for the Aleutians, the Alaska Peninsula, and
Bristol Bay and into the 30s for the rest of Southwest. Similarly,
temperatures will also trend warmer for Southcentral with areas
near the coast well into the 40s with 30s elsewhere.

Along with the frontal passage, should any precipitation form
over the Kuskokwim Valley, cool enough air remaining at the
surface could lead to mixed precipitation type forecast
challenges. Many locations across Southcentral that have been cool
and snowy lately, will likely see rainfall for the Thanksgiving
Holiday weekend. Copper River Basin will likely stay at or below
freezing. Southeast flow through the Gulf could downslope the
western Kenai Peninsula, Anchorage, and Mat-Su. While that could
mean less potential for precipitation, it could also mean warmer
than forecasted temperatures if that warm air mixes to the
surface. Precipitation type could be a challenge to forecast later
in the week, especially for areas of transiting temperatures
further inland and at higher elevations but enough warm air should
be established by the end of the week for a clearer delineation
of rain and snow.

A low moving north into the western Bering Sea is indicating at
least storm force winds with some hints of hurricane strength
potential Saturday. The front will then track east across the
Aleutians over the weekend, replacing the weakening low that was
over the eastern Aleutians from midweek. The progressive track
will generally be along the same trajectory that will continue on
a path right into the Gulf. For the early part of next week, QPF
will depend on the timing of the front into Southwest Alaska and
the position of the low moving into the Gulf. The phasing of these
two features Monday night could bring ample moisture to the
Susitna Valley.

rux

&&

.AVIATION...

PANC...VFR conditions and light winds will persist for most of the
TAF Period. Ceilings will likely drop down towards MVFR range
sometime later tonight as light snow also tries to work into the
terminal. There is quite a bit of dry air in place for
precipitation moving in aloft to overcome, and any snow that does
reach the ground should later this evening will stay at very low
intensity due to this factor.

AS

&&