Gale Warning 463, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
533 AM AKDT Fri Aug 11 2023

.ANALYSIS AND UPPER LEVELS...

A broad longwave trough anchored by a closed upper-level low over
the north-central Bering remains in place with little change from
what was observed yesterday. Several shortwaves are noticed on
Satellite rotating around the aforementioned trough towards
Southcentral. A developing low south of Nikolski is also observed
on Satellite and will intensify into a significant low for the
Gulf of Alaska on Saturday. Temperatures this morning have been
reported ranging from the upper 40s to the lower 50s across all of
southern Alaska.

&&

.MODEL DISCUSSION...

Models continue to be in good agreement on synoptic features
through the short-term and are coming into better agreement with
the strong low forecasted to impact the Gulf of Alaska Saturday.
There is high confidence of widespread gales along the leading
front, but the exact timing of stronger winds and their spatial
distribution remains a challenge.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. Gusty
Southeasterly Turnagain Arm winds are possible beginning Friday
afternoon.

&&

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

Some clearing along the Cook Inlet coast of Kenai Peninsula has
promoted patchy fog from Homer to Kenai this morning. This could
last through the rest of this morning. Low confidence for fog
development from Anchorage north through the Susitna Valley.
Surface low pressure in the northern Gulf is keeping showers
across portions of Southcentral today. Clearing skies across the
Susitna Valley may promote convective activity and thunderstorm
development this afternoon. Southeasterly winds through the Knik
River and Turnagain Arm may promote higher gusts in Anchorage and
the Matanuska-Susitna Valley.

A broad, North Pacific low is set to enter the Gulf of Alaska
Saturday morning, though the associated strong front moves into
the southern Gulf this afternoon and will track north towards the
coast tonight into Saturday morning. Confidence is high for areas
of high end gale force winds with storm force gusts along the
north Gulf coast, and widespread gale force winds along the rest
of the western Gulf. Sustained storm force winds will be possible
as the barrier jet strengthens and winds press against the coast.
Southeasterly winds could stream into Prince William Sound at 30
kts Saturday afternoon and evening. Additionally, strong northerly
flow through Cook Inlet is likely throughout Saturday, with a
period of storm force gusts Saturday morning. The strongest winds
are expected by early Saturday morning, with north- northeasterly
winds 40-45 knots likely and as high as 50 knots possible.
Corresponding seas along the north Gulf coast will range from 14
to 18 feet, with seas ranging from 18 to 25 feet across the rest
of the western Gulf through Saturday night. Substantial
precipitation is expected with this low, especially for areas near
the coast. From around midnight Saturday through Sunday morning,
areas inland could expect less than a quarter inch, but Kodiak and
Seward could be reaching for two inches, Cordova between two and
three, and Whittier between three and four inches. Through the
rest of this weekend, southwesterly flow and continued unsettled
weather is expected.

&&

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

A large upper-level low pressure system over the Bering Sea
continues to dominate the pattern for the Aleutian Chain and
Southwest Alaska in the near future. The overarching circulation
is driving much of the unsettled activity across the Central and
Western Bering Sea. Looking closer, an embedded low pressure
system within the broad circulation is driving much of the
precipitation observed just south of the Chain. A nearly inverted
trough is stretched out over Southwest Alaska currently, which has
lead to the cloudy regime with light showers observed much of
Thursday. However, today as the trough lifts out, so will more of
the clouds, increasing heating at the surface and allowing for
higher temperatures by this afternoon. Showery rainfall will be
more common throughout this weekend. The potential for isolated to
scattered thunderstorms will be present through this afternoon in
the northern portion of Southwest Alaska, namely the Lower and
Middle Kuskokwim Valley, and the northern stretches of the Greater
Bristol Bay area, eventually making its way into the Kuskokwim
Delta by early this afternoon. The potential for isolated to
scattered thunderstorms will arise again Saturday afternoon and
evening, however mostly over the Kuskokwim Delta region, as this
is expected to be where surface conditions will be most favorable
for thunderstorm development. Meanwhile, late this afternoon gusty
winds will pick up through the Kamishak Gap into the Greater
Bristol Bay region, lasting into tonight before shifting, pushing
offshore, and dissipating by early Saturday afternoon.

Back out west, the embedded low currently south of the Chain will
continue to move the the northeast, breaking away from the
partner low in the Bering, making way for the Eastern Aleutians,
Alaska Peninsula, and the Gulf of Alaska providing light rainfall
across these regions as it goes. By Saturday morning,
northeasterly wind flow will intensify along the southern Alaska
Peninsula coastline, reaching up to 35 mph before coming down by
Saturday afternoon. Out west, rain shower activity focuses near
the central Aleutians for the weekend as a weak, occluded low
tracks slowly south across the Chain. By Sunday afternoon, a
second consolidated North Pacific low arrives south of the Alaska
Peninsula, poised to continue active, wet weather into the
beginning of next week.

&&

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

The long wave trough over the Bering continues to steer the
weather across Southern Alaska, but is slowly weakening through
Thursday. The more active weather producers are moving in from the
North Pacific into the Gulf of Alaska for the first part of the
week, but a last surge of energy from the Bering trough pulls the
next following North Pacific low into Bristol Bay and the Eastern
Bering for Thursday. Widespread Rain and gusty winds expected from
the Aleutians and Alaska Peninsula into the Gulf.

Weather in the Gulf of Alaska will be busy through Thursday as
the first well developed low brings additional rain and gusty
winds, strongest just offshore in the coastal areas, diminishing
late Sunday. The following low sheds energy from Tuesday on to
bring gustier winds to the Gulf, but most of the active windy and
wet weather will break back to the west as this low moves across
the Alaska Peninsula into Bristol Bay through Thursday.

&&

SYNOPSIS AND MODEL DISCUSSION...nsc
SOUTHCENTRAL ALASKA...vr
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...cl
LONG TERM...kz