479
FXAK68 PAFC 120027
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
427 PM AKDT Thu Jul 11 2024

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

An upper level shortwave and associated surface trough are
lifting northwestward from Middleton Island toward Prince William
Sound this afternoon. These features look to weaken as they
approach the coast by evening; however, the easterly flow and lift
will allow for steady shower activity to persist into the evening
and nighttime hours for Prince William Sound and the coastal
mountains. Farther inland, isolated to scattered showers will be
possible through the evening hours from Cook Inlet north across
the Susitna Valley. This wave will also help to reinforce the gap
winds later today, with gusts around 30 mph likely through
Turnagain Arm and the Knik and Copper River Valleys.

Friday morning, a front will move into the western Gulf and
across Kodiak Island. A triple point low will then spin up along
the front near Kodiak Island. The front will continue to lift
toward the northern Gulf through Saturday as the surface low
drifts northeast along the Kenai Peninsula. These features are
tapping into abundant moisture from the Pacific with the
southeasterly steering flow ahead of the front advecting that
moisture across all of Southcentral through at least the first
half of the weekend. Given the predominantly southeasterly flow
ahead of the front, the highest precipitation amounts will be
along the coastal mountains and western Susitna Valley. For areas
in the lee of the Chugach Mountains, some rain will likely move
over these areas late Friday, as a weak wave moves ahead of the
main system and prior to the development of the strong cross-
barrier flow. Precipitation will then taper off and become much
lighter for overnight Friday into early Saturday before the trough
begins to lift north and the strong downsloping flow wanes,
allowing steadier precipitation to fill back in. Once the trough
lifts north, rain should also develop over the Copper River Basin.

Gap winds will be quite strong Friday afternoon and evening as
that initial wave moves north in tandem with a building coastal
ridge out ahead of the surface front. Winds could gust 30 to 40
mph through Turnagain Arm and across the Knik and Copper River
Valleys. Winds could gust to around 50 mph for the Anchorage and
Eagle River Hillsides.

There remains some model uncertainty as to how quickly the front
and its attendant upper-level wave move from the western Gulf to
the Northern Gulf. As such, the timing of the onset of precipitation,
especially for those locations in the lee of the Chugach, is
still a bit uncertain. Model uncertainty grows by late Saturday
into Sunday, as some guidance tries to kick out the trough faster
while other guidance lingers the trough and allow for enhancement
of precipitation into Sunday as a trailing upper-level wave
catches up to the first. Nonetheless, conditions look to remain
unsettled across much of Southcentral through the entire weekend.

-TM

&&


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

An upper level low north of St. Lawrence Island will remain
fairly stationary through early tomorrow afternoon before moving
southeast into Bristol Bay Saturday. Rounds of shortwaves moving
through the Aleutian Islands and the Southwest along the southern
part of this Low will bring periods of rain, clouds and foggy
conditions through at least the start of the weekend.

Current satellite and radar shows clouds over the Southwest as a
front exits the region. Surface observations reported a few
hundredths to a tenth of an inch of rain today. Current observations
show breezy southerly and southeasterly winds through the Aleutians
and Bristol Bay this afternoon. Frequent wind gusts ranging from
20 to 30 mph through Saturday in the Aleutians are expected as the
aforementioned shortwaves move through the area. A return to rain
showers and strong southeasterly winds over the Southwest return
late this evening as a front moves across the Southwest.
Southeasterly wind gusts tomorrow morning and afternoon ranging
from 25 to 35 mph as strong winds funnel through the Kamishak Bay
can be expected toward Iliamna and Port Alsworth.

-DJ

&&

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

On the Alaska weather map, a closed upper level low over the
Yukon Delta slips Southeastward into the Northern Gulf of Alaska
by the end of the forecast period. A major shortwave trough
extends across the Bering to a second weaker low exiting the
Russian Far East near Magadan. This low continues into the Western
Aleutians by Thursday. The upper level ridge across the Eastern
Interior weakens briefly but hold it place through the week.
Forecast model confidence remains good with only the occasional
trough rotating through the pattern to temporarily upset
continuity. Heaviest rainfall starts over Southwest Alaska Monday
and spreads Eastward. The Eastern portions of Southcentral Alaska
expects heavier rains along the coasts into Southeast Alaska by
Tuesday. Heavier rains develop across Cook Inlet, over the Kenai
Peninsula into Prince William Sound and Kodiak Island through
Thursday once the low moves into the Gulf. Lesser amounts of rain
will fall over Southcentral areas away from the coasts. The
Western Bering low spreads heavier rains into the Western
Aleutians on Thursday.

Kutz

&&

.AVIATION...

PANC...VFR conditions will persist through the TAF period. Gusty
southeasterly Turnagain Arm winds will slowly diminish overnight
and become light and variable Friday morning. A strong Bering Sea
front extending into the North Pacific will continue to lift
northeastward towards Southcentral Alaska through Friday evening
and Saturday. Gusty southeast winds will pick up again ahead of
this front Friday afternoon as the pressure gradient tightens.
Friday night and Saturday, flow becomes down-inlet dominant as a
triple-point low lifts northward near Kodiak Island. A few showers
could make it over the terminal Friday evening towards the end of
the TAF period when the initial push of moisture arrives.
However, VFR ceilings and visibilities should remain due to the
southeast flow.

&&

$$