Small Craft Advisory 55, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
536 AM AKST Wed Jan 17 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Friday night)...

Key Messages:

*  Widespread windy conditions across Southcentral Alaska today
   through Thursday morning with the strongest winds affecting
   the coastal communities of Valdez, Cordova, Seward, and
   Whittier.

*  Strong gusty winds will also develop in the Matanuska Valley
   later today, peaking overnight tonight through early Thursday.

*  Dry weather continues through the end of the week. Colder
   temperatures will settle in as winds lighten up Thursday
   through Friday.

A strong blocking ridge is centered over the Southwest Alaska
coast and eastern Bering Sea. A series of short-wave troughs are
digging southward along the eastern periphery of the ridge - from
the ALCAN border region southward into the northeast Gulf. As the
ridge continues to build eastward across mainland Alaska a north-
south oriented jet streak is strengthening right over Southcentral.
Cold air is advecting southward from the eastern Interior across
Southcentral and into the Gulf. All of this is leading to strong
and gusty gap winds through area mountain ranges, but strongest
through the coastal mountains due to tighter pressure and thermal
gradients between interior Southcentral and the northern Gulf.

The forecast for the next couple of days is on track with only
minor adjustments made in this morning's forecast updates. After
a peak in winds yesterday with passage of a short-wave and first
round of cold air advection, winds lightened up in many places
overnight. However, there are signs early this morning of
strengthening winds as the next round of cold air advection
commences. This trend will continue through the day across the
entire region as conditions become more and more favorable. The
one change of note was to delay the onset of winds in the
Matanuska Valley and north to west Anchorage until this afternoon
as the mean flow between the ridge and trough starts to veer from
due north to northeast and advect colder air from the Copper River
Basin southwestward through Tahneta Pass and the Matanuska River
Valley.

Winds will peak over Southcentral this afternoon through tonight,
then slowly diminish Thursday through Thursday night as the upper
ridge moves overhead and the Gulf trough/low exit southward into
the Pacific, allowing pressure gradients to slacken. Gap winds
will linger along the coast all the way through Friday. Where
winds do lighten up, temperatures will fall. Meanwhile, the upper
level ridge will retrograde westward over the Bering Sea Thursday
through Friday. This will allow an Arctic trough, with even colder
air, to drop southward across mainland Alaska beginning Friday
night.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days
1 through 3: Today through Friday night)...

High pressure extends from Interior Alaska across Southwest Alaska
and the Bering Sea, making for a relatively quiet morning across
the region. Some fog is present in portions of the Lower Kuskokwim
Valley, but dry northeasterly flow around the high is forecast to
gradually erode the fog through the day. Fog will generally not be
favored over the next few days, even as subsidence under the
upper-level anticyclone leads to a strengthening inversion since
the low-level atmosphere will remain dry and mixed by the
northerly winds. However, there will be some potential for stratus
to develop over the waters of the Bering Sea under the
strengthening inversion.

Along the southern periphery of the ridge, weak shortwave troughs
will lead to periods of light rain along the central and western
Aleutians through Thursday night. After that point, the ridge
shifts west, pushing any precipitation out of the region. Along
and near the Alaska Peninsula and the Aleutian Chain, the stagnant
pattern will continue to support 20 to 30 knot east to
northeasterly winds through the forecast period.

Looking ahead to the weekend, a blast of Arctic air dips across
Southwest Alaska and the eastern Bering Sea, leading to a high
chance for wind chills in the 20s to 30s below zero and extreme
freezing spray from Bristol Bay to St Matthew Island through
Tuesday. There is also a moderate chance for some locations in
southwest Alaska to see wind chills as low as 40 below zero.

CQ

&&

.LONG TERM FORECAST (Days 4 through 7: Saturday through Tuesday)...

An upper level ridge centered in the Western Bering and extending
across most of Western Alaska weakens and moves Southwest through
the forecast period. Models and ensembles are in good agreement
through Tuesday. Weak impulses sliding along the top of the ridge
flatten out the Northern edges and help develop an elongated upper
level trough through the Eastern Interior and down into the Gulf
of Alaska. These features combine to drag arctic air over Interior
Alaska and into Southcentral and Southwest Alaska through Monday.
Scattered snow showers and potentially strong gusty Northerly gap
winds will accompany the Bora-like cold air advection across
Southern Alaska. With the continuing weakening of the upper ridge,
a closed low center develops in the Gulf of Alaska for the new
week, bringing locally heavy snow showers over the Eastern Kenai
Peninsula, Prince William Sound and the coastal areas over to the
Canadian border on Monday. Precipitation is not expected to move
very far inland due to the denser cold and dry air from the
Interior.

Kutz

&&

.AVIATION...

PANC...VFR conditions will persist through the TAF period. Winds
will initially be light and out of the north through the early
morning hours. Fog currently over the terminal early this morning
should begin to scour out in the next couple of hours as winds
begin to increase.

Northerly winds will pick up the rest of the morning and throughout
the day with gusts likely in the 20 to 30 kt range in the
afternoon and early evening. These gusty northerly winds look to
peak overnight tonight into early Thursday morning. Although not
likely, there is a low chance (20%) of a gust to 35 kts during
this time. The pressure gradient will relax into through the mid-
morning hours Thursday and winds should be begin to diminish as
well.

&&