Gale Warning 439, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
514 PM AKDT Tue Aug 16 2022

.ANALYSIS AND UPPER LEVELS...

A high amplitude pattern remains in place over the Alaska region,
with a trough centered over mainland Alaska and the northeast
Pacific and a short-wave trough and associated surface low riding
overtop of a flat ridge sitting over the north-central mainland.
Embedded within the larger trough, a series of short-waves over
the Gulf of Alaska are lifting northward across Southcentral
Alaska. A moderate strength surface low is weakening as it tracks
toward Kodiak Island, with an occluded front pushing onshore along
the north Gulf coast. This is leading to a gale force barrier
jet, with marginally weaker winds spreading into Prince William
Sound and nearby bays and passes. Radar imagery shows areas of
rain spreading inland with the upper short-waves, with the
heaviest rain in the coastal zone. Rainfall rates are quite a bit
lower compared with recent days and there are no flooding concerns
at this point in time. Meanwhile, a strong short-wave trough is
digging southward along the Southwest Alaska coast, with areas of
rain spreading inland from the Kuskokwim Delta to the Kuskokwim
Valley. Cold air advection on the back side of this is beginning
to elevate winds along the Kuskokwim Delta coast. The short-wave
and surface low crossing the southern Bering Sea are moving fast,
bringing a real quick shot of rain, isolated gales and small
craft advisory level winds to the Aleutian Islands.

&&

.MODEL DISCUSSION...

Models continue to struggle mightily with details of the short-
wave digging across Southwest Alaska and interaction with
downstream short-waves over the Gulf. Run-to-run consistency is
quite poor with which, if any, short-waves phase as everything
lifts northward across southern Alaska Wednesday/Wednesday night.
This will affect timing and location of heaviest rainfall as well
as gap winds over Southcentral. As a result, forecast confidence
with these details for Wednesday is low. Out west, the GFS is a
bit of an outlier with a slower, deeper solution with the low
crossing the southern Bering Sea Thu/Fri and will be disregarded
for the time being. All-in-all, that system and forecast is on
track.

&&

.AVIATION...

PANC...Deep southeast flow will maintain VFR ceilings/vis at the
terminal, even if rain occasionally makes it across the mountains.
A front will push inland sometime late Wednesday afternoon or
evening, with extremely favorable conditions for gusty southeast
Turnagain winds to move into the terminal. However, there is quite
a bit of spread in solutions with supporting upper level wave and
passage of surface front. While the latest TAF does reflect
winds, would expect further updates to be made to the timing of
these.

&&

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

An upper level low positioned in northwest Alaska and another
upper low south of Kodiak Island will keep Southcentral in a
southerly flow pattern for the week ahead. A couple of weak
embedded shortwaves in the southerly flow is spreading moderate to
heavy showers along the coast, with lighter amounts further
inland due to downsloping. Heading into tonight, another shortwave
rotating around the aforementioned upper low near Kodiak moves
northward into Anchorage, bringing another chance of rain. As the
upper low elongates and pushes inland on Wednesday, some weak
instability and midlevel ascent will bring the potential for wet
thunderstorms across the Alaska Range, Talkeetna Mountains, and
along the northern Susitna Valley during the afternoon and evening
hours. Meanwhile, a surface low will also move into the Kenai
Peninsula, with another round of rain expected along the northern
Gulf coast. By Wednesday, there is considerable model uncertainty
and positional differences with this system, but the main theme
will be continued cool, cloudy, and wet conditions for the rest of
the week.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today
through Friday morning)...

An upper-level low is located over Northern Alaska this morning,
and a shortwave continues to pinwheel around the southern side of
the low across the Y-K Delta. As a result, winds and rain will
persist for the next few days, and the low itself will enhance
rainfall as it drops south over Southwest on Wednesday.
Precipitation will start to clear by Thursday morning as the upper low
exits to the northeast. Expect drier conditions and generally
cloudy skies to persist for Thursday through Friday morning while
the next system approaches from the west. A large front is
expected to near the Southwest coast on Friday morning.

&&

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

A deep low near the Kamchatka Peninsula extends its front and
associated upper-level shortwaves across the western and central
Bering/Aleutians this morning. Steady rain and stronger southerly
winds with the front will continue spreading east through
Wednesday morning, at which time the front and associated low exit
into the North Pacific.

Another large, deep low will enter the domain from the west
on Wednesday. Rain is expected to begin for the western Aleutians
starting Wednesday morning with the arrival of the front. By
Thursday morning, the low center will be located near the tip of
the western Aleutians and heavy rain will encompass much of the
western and central parts of the domain. Gale force winds will
also develop along the backside of the low. By Friday morning,
the center of the low will track to the central Bering and its
front will near the Southwest coast. Expect rain and stronger
winds with this feature to persist through the end of the
forecast period.

&&

.MARINE (Days 3 through 5: Friday through Sunday)...

Gulf of Alaska: A front pushes into the western Gulf on Friday
and tracks slowly north and east. Winds may increase to gale force
by Saturday night and persist into Sunday, especially near the
Barren Islands and in Kamishak Bay. The timing of this frontal
passage remains uncertain, though confidence in winds reaching
this criteria has increased to moderate. Seas are expected to
remain less than 20 ft.

Aleutians/Bering: A low in the central Bering is likely to be
accompanied by gale force winds wrapping around the center on
Friday. Northerly gales across the western Bering curving to
westerly across the western and central Aleutians diminish as the
low reaches the eastern Aleutians Friday night. Some northerly gap
winds may reach gale force across the eastern Aleutians through
Saturday. Seas approach 25 ft on the Pacific side of the western
Aleutians Friday morning. Seas to 20 ft may persist in the
vicinity of the low center through Friday afternoon before
subsiding. Confidence is high.

&&

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

A large, broad low traversing the Bering/Aleutians near the end
of this week will park itself south of the Alaska Peninsula for
the weekend and start of next week as it gradually winds down.
Though the upper-level pattern breaks down briefly late this week,
by Saturday, a large vertically-stacked low crossing the Bering
will slow to a halt near the Alaska Peninsula, re-anchoring the
longwave trough axis roughly over the western half of the state,
where it sits currently. This will continue the same general
pattern that has been so persistent this month, with cloudy, rainy
conditions across the southern mainland.

Over the weekend, Southwest Alaska looks wet and windy as the
low’s front makes its first push inland. Portions of the western
Gulf will see enhanced upslope rainfall along the front, as well
as windy conditions, especially through the Barren Islands and
Kamishak Bay/Gap as the front creeps north and eastward.
Southcentral Alaska may have some hope for a relatively drier
weekend, though, as an upstream ridge looks for an opportunity to
nudge in on Saturday. With moist southerly flow still in place,
however, the north Gulf coast is likely to remain wet with rain
showers, especially as the front trudges closer on Sunday. By
Monday, the global models generally agree on the arrival of the
front along the north Gulf coast, leading to the return of
moderate-to-heavy rain, with intermittent showers bleeding over to
inland regions. By Tuesday, the front pushes inland, with
increased instability from an upper-level shortwave leading to
more widespread rainfall for interior Southcentral. The timing of
the arrival of the front comes with some uncertainty, however, as
the trend in model guidance over the past few days has been to
slow the progression of both the low and the front. For the
central and eastern Aleutians, northerly winds and below average
temperatures remain a fixture for the long term forecast period,
while high pressure with stratus and fog prevails over the western
Aleutians.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gales: 119, 176, 411, 413.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SEB
SOUTHCENTRAL ALASKA...MF
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CJ
MARINE/LONG TERM...CQ