506
FXAK68 PAFC 130032
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
432 PM AKDT Sun May 12 2024

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

Cumulus cloud development is apparent on satellite across the
entire region. Reflectivity on radar points towards widely
scattered showers, but reports of any rainfall have been light and
dew point depressions suggest that many of the showers are virga.
Some of the cumulus is developing into cumulonimbus and those
should produce rain that reaches the ground. Pressure is expected
to increase over mainland Southcentral for the first half of this
week, yielding to quieter weather overall. Southerly winds through
Turnagain Arm, Cook Inlet, and the Copper River Valley will
decrease tonight and remain light for most over the next couple
days.

Weak upper level forcing combined with increasing breaks of
sunshine and weak instability will produce isolated to scattered
showers across the region. Meanwhile, a weak low and short-wave
south of the eastern Aleutians this morning will track quickly
along the base of the long-wave trough into the Gulf tonight. This
will bring a quick shot of rain to Kodiak Island, mainly the east
side of the island Monday morning. The low will remain offshore
as it continues across the Gulf through Monday night, with little
or no precipitation from this synoptic feature reaching the north
Gulf coast.

As pressure rises over the next couple days and the Gulf low
pushes east, coverage for showers will become more isolated on the
Kenai Peninsula, Anchorage, and MatSu Valley. Diurnally driven
showers will continue to remain possible over the Copper River
Basin. The warmest, sunniest, and driest day of the week should be
Wednesday, ahead of the next front expected to reach the western
Gulf late Thursday morning.

&&

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

A weak, elongated low south of the Alaska Peninsula this
afternoon is producing areas of light rain and northerly small
craft winds moving quickly toward the southern Gulf. Behind this
low, quieter conditions and northerly flow spread across the
Bering Sea and Aleutians, while a strong upper ridge builds into
place behind the low.

This has not developed enough to produce lightning, as forecast
soundings show a relatively warm, dry layer in the mid to upper
levels that have kept showers low-topped today. Additional rounds
of showers will be possible on Monday, mainly near the Alaska
Range out ahead of a shortwave trough digging south around the
developing Bering ridge. However, instability looks even more
marginal on Monday, and thunderstorms are unlikely.

Attention shifts to a much stronger system poised to affect a
large portion of the outlook area later in the week. By Monday, a
strong 970s-980s mb low moving off of Kamchatka will extend a warm
front into the western Aleutians, with southerly winds in the gale
force range behind the initial front across the western Aleutians
and Bering A cold front will move in quickly behind the warm
front and begin to occlude it on Tuesday morning, while the parent
low moves farther into the far northern Bering Sea. Gale force
southerly winds will spread east towards the central Aleutians and
Pribilofs, while winds remain strong but turn westerly behind the
cold front. Bands of of light rain following both frontal
features should also shift from the western Aleutians to the
central Aleutians and past the Pribilofs on Tuesday.

By Tuesday night, the main low and trailing front will begin to
weaken as the low center moves up towards St Lawrence Island.
Even so, guidance is beginning to show the wind field holding on
for longer, and there is potential for 30 to 40 mph southerly
winds to reach the Southwest coast as early as Tuesday afternoon,
especially near the Kuskokwim Delta. It is too early at this time
to determine exact potential for higher than normal water levels
moving in with this system. However, coastal communities across
the Kuskokwim Delta should continue to monitor the forecast for
updates over the next couple days while we continue to follow this
strong spring low pressure system.

&&

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

For Southcentral...

The long term for southcentral Alaska will begin with ridging in
place across much of the eastern mainland, resulting in fairly dry
conditions and temperatures at or just above climatological average.
Afternoon showers will be possible during the afternoon in close
proximity to the mountains, particularly the Wrangells. Deep upper-
level troughing then shifts east across southcentral Alaska by
Friday, bringing increased cloudiness, coastal rain, and high-
elevation snow to the area. Present forecast guidance keeps this
system only precipitating on Gulf communities and in the mountains,
though there is a chance the system will shift north, bringing wider
spreading rains to the mainland. Overall, temperatures will continue
to rise, with daytime highs warming with the exception of Friday,
which is likely to be the coolest day of the forecast period.

For Southwest and the Bering/Aleutians...

By Thursday, confidence is high troughing will exist across the
eastern Bering, Aleutians, and into southwest AK. However, models
diverge significantly with regards to potent shortwave trough
rounding the base of the longwave trough. The 12z operational GFS
run brings a low into southwest low that would result in the
potential for low-elevation snow and windy conditions. Meanwhile,
the ECMWF and Canadian models move that energy a bit farther south.
Upper-level ridging is likely to build in behind the trough as it
shifts east. The exception to this is across the western Aleutians,
where continued storminess is likely.

&&

.AVIATION...

PANC...VFR conditions will prevail through the TAF period.
Southeasterly winds out of Turnagain Arm late this afternoon will
continue to bend into the terminal with pressure gradients
continuing to be favorable as a low pressure system passes south
of Kodiak and re-orients the coastal ridge to the favorable east-
to-west direction. Winds could gust between 20mph to 30mph this
evening before dying down overnight. Winds turn light and out of
the north Monday morning.

&&


$$