Gale Warning 460, NWS Anchorage, AK

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

.ANALYSIS AND UPPER LEVELS...
There are a lot of small features on satellite over the forecast
area this afternoon. The main anchor is the low over the central
Bering Sea. The jet stream is running south of the Aleutians,
Alaska Peninsula, and Gulf of Alaska. An inflection point on the
jet south of Adak early Thursday afternoon is where the surface
low is developing which will intensify into a significant low for
the Gulf of Alaska on Saturday.

Satellite shows two smaller lows over the Gulf this afternoon with
the more impactful one for Southern Alaska just west of Middleton
Island with some strong showers associated with it. There are a
few upper level waves embedded in the easterly flow crossing the
Chugach and Kenai Mountains. This will keep showers around these
areas until the low weakens on Friday. The area with the best
chance for thunderstorms this afternoon and evening is the Susitna
Valley. The northern Kenai Peninsula and Copper River Basin also
have a chance for an isolated thunderstorm, but the Susitna is in
the best position today.

&&

.MODEL DISCUSSION...
Models are coming into better agreement with the low currently in
the northern Gulf and moving westward. The waves embedded around
this low vary with the hi-res models, but overall they are
locking onto a larger wave moving westward over the Gulf coast and
Coon Inlet this evening and then moving the areas of convective
uncertainty into Southwest Alaska for Friday and Saturday.
For the low moving into the Gulf on Saturday, the GFS probably has
the best lock on the track and timing of this system.

&&

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

&&

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

Weak low pressure resides in the Gulf of Alaska today into tomorrow,
with a series of upper level disturbances rotating around it,
producing widespread rainfall along the north Gulf coast. Clearing
skies across the Susitna Valley and Copper River Basin may
promote convective activity and thunderstorm development this
afternoon as well as tomorrow afternoon. There is a lesser chance
for thunderstorms along interior Kenai Peninsula, which requires
more clearing this afternoon than is currently being observed.
Satellite is not showing favorable conditions.

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 Friday afternoon and will track north towards
the coast Friday night 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. 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. 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.

&&

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

A broad, weak low in the central Bering Sea will track southward
to the central Aleutians 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. Tonight, rain showers are expected to
focus along a shortwave tracking west from Southcentral Alaska,
bringing a disorganized band of showers from the Western Alaska
Range this evening into interior Bristol Bay tonight. These
showers push toward the coast on Friday, with a more unstable
airmass forecast to move in behind it. This will allow for a
decrease in cloud cover, which will support isolated to widely
scattered thunderstorms over much of interior Southwest Alaska
(including more interior portions of Bristol Bay and the Kuskokwim
Delta) for Friday afternoon and evening. There continues to be low
confidence with various weak shortwaves retrograding across
Southwest Alaska, which limits the ability to pinpoint the main
focus regions for convection. Regardless, these storms will
likely develop within an environment with 20 to 30 knots of
surface to 6 km bulk shear, which should lead to the development
of clusters of more organized storms that track long distances
across Southwest Alaska (aided also by a 20 knot easterly storm
motion).

At the same time, an unseasonably strong North Pacific
low will track into the western Gulf of Alaska. Gusty winds will
develop through Kamishak Gap and interior Bristol Bay ahead of the
low on Friday. Rain and winds up to gale force will arrive south
of the Alaska Peninsula by the evening hours. As the low tracks
north, Kamishak Gap winds will weaken somewhat and shift out of
the north by Saturday morning. Some rain may then begin to spread
across the Alaska Peninsula, into Bristol Bay, and along the
Western Alaska Range as the low pushes its front into Southwest
Alaska. However, strong cross-barrier flow may limit the coverage
and intensity of precipitation. Isolated thunderstorms will again
be possible on Saturday, with the focus shifted west, toward the
Kuskokwim Delta, as more stable air works in from the east. Rain
showers are expected to linger through Sunday as the Gulf low
continues to extend its influence across Southwest Alaska.

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 the 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 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...EZ
SOUTHCENTRAL ALASKA...KM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CQ
LONG TERM...MK