Gale Warning 459, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
548 AM AKDT Thu Aug 10 2023

.ANALYSIS AND UPPER LEVELS...

A broad, weak low anchoring a longwave trough remains in place
over the north-central Bering and can be noticed on Satellite
Imagery. Troughing extending eastward from the low over Southwest
Alaska will remain in place through today, resulting in continued
chances for rain showers in the forecast for the region. Several
shortwaves are rotating around the low, resulting in widespread
shower activity on all four radars across southern Alaska. Cloudy
skies are also being observed across most of southern Alaska as
the trough continues to dominate the sensible weather across the
region.

&&

.MODEL DISCUSSION...

Models continue to be in good agreement on synoptic features
through the short-term. The main forecast challenges continue to
be with the timing and placement of shortwaves as they round the
trough in the Gulf and become easterly waves over Southcentral and
Southwest Alaska. This could provide enough dynamic support for
thunderstorms across the Coper River Basin and also the Kuskokwim
Valley and Delta. While models are coming into better agreement
with the track of a strong gale-force low in the Gulf of Alaska,
uncertainty remains with the timing of stronger winds and their
spatial distribution.

&&

.AVIATION...

PANC...MVFR conditions will continue this morning, improving to
VFR conditions by late morning. VFR conditions with light winds
are expected through the TAF period.

&&

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

Generally unsettled weather will continue through Friday as weak
disturbances rotate around a low in the Gulf of Alaska.
Southeasterly flow will keep moisture moving across the area.
Showers will begin to taper off later this afternoon throughout
the evening as southeasterly flow begins to downslope across the
Chugach Mountains near Anchorage and the Copper River Basin.
Isolated thunderstorms could fire off this afternoon across the
Susitna Valley and the western Kenai Peninsula with plenty of
convective potential. It would take a little more lift to set off
thunderstorms over the Kenai, so there is lower confidence for
that area. As for the Anchorage and Matanuska Valley, there is
some convective potential, but it appears unlikely for anything
more than isolated showery downpours.

A more energetic low system develops south of the Aleutians
toward the end of week. Its front reaches the Gulf late Friday
with the low center following behind on Saturday. Models are
nudging westward, but there is still a fair amount of model spread
with implications to the wind field and QPF. The core of water
vapor transport is headed for southeastern Alaska, but confidence
is increasing for Southcentral to expect heavier, stratiform
rainfall with gale force winds along the coast. Forecasted wind
gusts will peak at storm force, but the potential for sustained
winds to reach storm force along the northern Gulf Coast cannot be
ruled out at this time.

&&

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

A broad, weak low in the central Bering Sea will track southward
to the central Aleutians by this weekend. Troughing extending
eastward from this low over Southwest Alaska will remain in place
through today, which will keep chances for rain showers in the
forecast for the region. However, breaks in sky cover will allow
for increasing daytime high temperatures each day. This will
support isolated thunderstorms over much of interior Southwest
Alaska (including more interior portions of Bristol Bay and the
Kuskokwim Delta) for Friday afternoon and evening. Dynamic
support will likely be provided by further weak shortwaves
retrograding across Southwest Alaska as the low in the northern
Bering drops south toward the central Aleutians. As guidance
continues to struggle with the timing and placement of these
weaker shortwaves, forecast confidence remains lower regarding
the exact location of showers and thunderstorms.

At the same time, an unseasonably strong North Pacific
low will track into the western Gulf of Alaska. Initially, this
will lead to the development of gusty easterly winds for interior
Bristol Bay as air is forced through Kamishak Gap. As the low
tracks north, these winds shift out of the north for Friday night.
Rain should make its way over the Alaska Peninsula, into Bristol
Bay, and along the Western Alaska Range as the low pushes its
front into Southwest Alaska. As model agreement improves,
confidence is increasing that marine areas east of the Shumagin
Islands will see northeasterly gales, and that the heaviest
precipitation will remain outside of Southwest Alaska.

&&

.LONG TERM FORECAST (Days 4 though 7: Sunday through Wednesday)...

Overall unsettled weather pattern continues across the region
into midweek, with all models in close agreement. Bering low moves
closer to the Aleutians, with a number of short wave troughs
rotating around the low. This brings showers and some gusty winds
to most locations over the Aleutians and Alaska Peninsula. A well
developed North Pacific low center moves into the Gulf to the East
of Kodiak Island early Sunday, moving to the North Gulf Coast for
Monday. This low brings considerable rain and gale force winds
over Kodiak Island for Sunday, and to much of the Gulf and Copper
River Delta through Monday. Another well developed North Pacific
low follows late Monday closer to Kodiak, with similar conditions
into Wednesday.

&&

SYNOPSIS AND MODEL DISCUSSION...NSC/CC
SOUTHCENTRAL ALASKA...VR
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KC/CQ
LONG TERM...KZ