Gale Warning 547, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
536 AM AKDT Mon Aug 19 2024

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

An deep upper level trough axis now extends across much of
Mainland ALaska down into Southcentral and much of the Gulf this
morning. The frontal system that moved across much of Southcentral
with periods of rain and very gusty southerly winds has since
moved out to the eastern edge of the Copper Basin, and will soon
exit into the Yukon later this morning. Precipitation and even
much of the cloud cover in place near the front yesterday has also
mostly cleared out, with just a few showers drifting near the
Talkeetnas for the time being.

By this afternoon, the main upper trough will dig southeast
towards the northern Gulf and Prince William Sound as several
smaller embedded waves rotate around the primary trough from
mostly west to east. These passing waves coupled with fairly cool
air aloft in the mid levels will help widely scattered showers
develop as the profile becomes more unstable with daytime heating.
The best chance for shower activity will be focused over the
Copper Basin and the Mat-Su Valleys, but a few showers could drop
south all the way down into Anchorage and interrupt what will
otherwise be a relatively mild and partly to mostly sunny day.
Winds will also shift from gusty and southerly to briefly more
light and variable through early this afternoon, except where
westerly gap winds are already developing near Kachemak Bay and
down towards Kodiak Island. Gusty west to northwest winds will
pick up elsewhere this afternoon into tonight as prevailing flow
turns more northwesterly and an offshore pressure gradient
tightens, particularly where enhanced by gaps in terrain near
Whittier, Seward and Thompson Pass.

For Tuesday, generally mild conditions with winds slowly relaxing
through the day can be expected as an upper level ridge shifts
into place from the west. However, this ridge axis will continue
to shift east of our region from Tuesday night into Wednesday,
allowing for the next chance for rain to approach with a front
associated with the extratropical remnants of Ampil tracking out
across the Bering Sea. There is still some uncertainty regarding
how strong this front will be as it moves into the Cook Inlet
region, as well as how much moisture will be pulled north ahead of
it, but at least the western half of Southcentral will likely see
some amount of light rain with this front as it moves in late on
Wednesday afternoon.

-AS

&&

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

Conditions are quieting down in the wake of the past several days'
heavy rain and coastal flood events. As the weakening low tracks
further into Interior Alaska this morning, it pushes a broad cool
air mass across Southwest Alaska, leading to gusty, but gradually
diminishing, westerly winds and isolated rain showers which will
taper off through the day. A Flood Warning remains in effect
through 6pm this evening for high water levels along the lower
Kuskokwim River. While storm surge, and hence the up-river
push/backing up of water, has relaxed, water levels remain high
along the lower Kuskokwim River. The high tide cycle today could
bring another day with water levels similar to Friday and
Saturday, when some coastal communities reported flooding and
rapid bank erosion.

Otherwise, generally calmer conditions should prevail with a broad
area of high pressure shifting rapidly from the eastern Bering Sea
over Southwest Alaska today. Out west, the extratropical remnants
of Typhoon Ampil track into the western Bering, bringing storm
force winds. Winds quickly increase this morning for the western
Aleutians, with the potential to experience peak wind gusts of 75
mph around midday, particularly in Shemya. Warm advection out
ahead of the low contributes to stable conditions which will allow
for an expanding shield of fog and stratus.

Ex-Ampil tracks toward Chukotka for Tuesday with storm force
winds persisting near its center. Its front pushes into Southwest
Alaska, bringing a brief shot of rain, generally three tenths of
an inch or less, with the highest totals along the Kuskokwim Delta
coast and in portions of the Lower Kuskokwim Valley through
Tuesday night. Southerly winds along the Kuskokwim Delta coast
remain below gale force and develop and diminish rapidly, so are
not likely to produce significant coastal flood impacts. However,
as the low tracks into the Bering Strait for Wednesday, winds will
shift out of the southwest and approach gale force north of
Nunivak Island. Therefore, there is some potential for minor
coastal flooding, particularly north of Kipnuk, and likely focused
in and around Newtok. Stay tuned for further updates to the
forecast as we track the evolution of the remnants of Ampil.

Quesada

&&

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

The former Tropical Storm Ampil will have moved into the Bering
Strait on Thursday. Generally zonal flow through Friday across the
Bering with several disturbances rotating through the flow. An
upper level trough sweeps from the eastern coast of Russia on
through the forecast period. The trough reaches the western
mainland of Alaska on Saturday and bisects the interior for
Sunday. A surface front develops over western Alaska and moves
into the Gulf of Alaska and interior by Sunday. An upper level low
will form off of Kamchatka on Sunday and become our next weather
maker after the end of the forecast period.

Generally widespread gusty winds across the Bering accompanies
the formation of the front into western Alaska, dissipating late
Friday. The front spreads a wide swath of locally heavy rain
across the western half of Alaska for Thursday and diminishes as
the front moves through the interior. On the tail end of the
front, an elongated band of locally heavy rains will impact the
Aleutians and Alaska Peninsula through early Friday. As the front
passes through Southcentral, it will form a low pressure system
over the Northern Gulf, which will trigger moderate to heavy rain
across Prince William Sound and the Copper River Delta for the
rest of the forecast period. A well developed low pressure system
in the eastern North Pacific will bring heavy rain and strong
winds for next week.

-JR

&&

.AVIATION...

PANC...VFR conditions persist. Gusty southwesterly wind diminish
later this morning, then become northerly (but not nearly as
intense) later this evening.

&&