480
FXAK68 PAFC 070027
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
427 PM AKDT Mon May 6 2024

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

A low is moving across the northern Gulf of Alaska, bringing
isolated to scattered showers across the northern Gulf and through
Prince William Sound. A band of more steady rain is across Cook
Inlet this afternoon and oriented from around Kenai northward to
the Susitna Valley. Rainfall has cleared from the Anchorage area,
though cloudiness remains. The Copper River Basin is mostly sunny
with gusty winds to 30 mph. Diurnally driven cumulus clouds are
developing along the foothills of the Wrangells and the Alaska
Range.

The band of rainfall is expected to continue west and dissipate
through this evening, though stray showers could linger overnight,
primarily for higher elevations of the Alaska Range and the
Wrangell mountains. Coastal areas could also get some stray
showers. Another round of precipitation is expected to return
across most of the northern Gulf and Prince William Sound Tuesday
as a trough lifts inland. Another low will track similarly into
the Gulf for Tuesday and Kodiak will have precipitation return
Tuesday through Wednesday morning. The front will continue
northward with increasing chances for Southcentral through
Wednesday night. A band of precipitation could develop over
Anchorage Wednesday evening.

Cooler air will advect through Southcentral following the low
and some areas of higher elevations could see a mix of rain and
snow or even all snow. For passes across Southcentral (Thompson,
Turnagain, Moose), snow is possible overnight Wednesday through
Thursday morning. While the forecast is pointing toward snow
chances, confidence is low at this time.

With the progression of lows moving through the Gulf over the
short term, south to southeasterly flow at times will promote
gusty winds through gaps in terrain for communities around
Turnagain Arm, Knik River, and Copper River Valley. Winds
could gust 20 to 30 mph.

rux

&&


.SHORT TERM FORECAST SOUTHWEST ALASKA, THE SEA AND THE ALEUTIANS
(Days 1 through 3)...

Unsettled conditions with areas of mixed rain/snow will continue
across much interior Southwest Alaska through midweek as a stalled
surface boundary remains draped from near King Salmon to north of
Aniak. These areas of showers will be enhanced both Tuesday
morning and again Wednesday as a series of weak upper-level waves
moves across the region from the west.

These waves are moving out ahead of the main upper-level, longwave
trough situated over the eastern half of the Bering. A potent
shortwave trough will move south from the Bering Strait Tuesday
morning to the Pribilof Islands by Wednesday morning. This feature
will deepen into an upper-level low. This, combined with cold,
dense air near the surface advecting from the Gulf of Anadyr over
the northern Bering, will result in the development of compact
polar low. While guidance continues to struggle with the exact
timing and track of this feature, it will most likely deepen
rapidly as it moves from west of Saint Matthew Island south toward
the Saint Paul Island.

A core of gale-force winds and storm-force gusts are likely along
the western flank of the low, with gales persisting along the way
to the eastern Aleutians for late Wednesday. A core of snow will
also accompany this system. Again, the exact set up remains
uncertain, but a track over or very near the Pribilofs could
bring at least some measurable snow along with gusty winds.

This low reaches Bristol Bay for Thursday with showers for the
AKPen and Bristol Bay coast. Another deep low moving east from
the Kamchatka Peninsula will push a gale-force front across the
western Aleutians for Wednesday and the central Aleutians for
Thursday.

-TM

&&

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

The longterm forecast begins on Friday with broad troughing
continuing to stretch from the western Aleutians into the Gulf of
Alaska, with multiple upper-level shortwaves embedded within the
flow. At the surface, a system weakens over Southcentral on Friday
while an expansive low encompasses much of the Bering and the
Aleutians. This low is associated with a potent upper shortwave
that forms into a closed upper low and lingers near the Alaska
Peninsula through at least the weekend. Multiple shortwaves rotate
around the low as the attendant surface low gradually drifts
closer to the Gulf of Alaska. As a result, precipitation is
expected for Southwest Alaska, the Gulf, and the northwest Gulf
coast for Friday and Saturday. Precipitation will especially be
focused on the upslope sides of the mountain ranges while lower
lying valley areas should stay on the drier side of things. By
Sunday, the low`s front spreads across the entire Gulf coast and
still portions of Southwest Alaska, however models struggle with
regards to the placement of the low center. The GFS keeps the low
further west near the eastern Bering/Alaska Peninsula, while the
CanNH and EC bring the low east into the Gulf. The GFS solution
keeps the precipitation a bit steadier along the Gulf coast while
the others break the system up over land, lessening the chances of
precipitation.

&&

.AVIATION...

PANC... Southeasterly winds out of Turnagain Arm are expected to
develop once again this evening and persist into the overnight
hours. With cooler temperatures and extensive cloud cover in
place, the atmosphere is more stable than it has been in recent
days, so there is uncertainty in the duration of the gusty winds;
it could be briefer than indicated in the TAF. Wednesday afternoon
looks like another marginal day for the Turnagain winds, with the
terminal on the northern periphery of the Turnagain Arm jet.
Still, with marginally higher temps/instability, do think some
gusty winds will develop by 00Z. Meanwhile, VFR ceiling/vis and
dry conditions will persist.

&&

$$