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208
FXAK68 PAFC 260019
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
419 PM AKDT Sat May 25 2024

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

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A weak low in the Gulf of Alaska will track slowly southward over
the next several days, allowing weak ridging to work in over
Southcentral Alaska. As the low dips southward, its front,
currently just off the north Gulf coast, will retreat, allowing
precipitation to taper off tonight along the coast. Drier
northerly flow over Southcentral has brought with it warmer
temperatures and sunnier skies, yielding modest instability which
will continue to fuel rain showers across the Susitna Valley,
Copper Basin, and moving in from Yukon. Conditions are very
marginal for thunderstorm development, but an isolated lightning
strike or two from a particularly strong shower cannot be ruled
out. The more stable airmass over Cook Inlet, indicated on
satellite by a lack of clouds this afternoon, is likely to prevent
much in the way of shower activity for Anchorage and the western
Kenai Peninsula.

Tonight, an upper-level easterly shortwave will track from near
Yakutat into the eastern Copper River Basin, bringing a band of
steadier rainfall. This feature will propagate east to west,
pushing toward the Talkeetna Mountains, Anchorage, and the Kenai
Peninsula for Sunday, though its impacts are somewhat uncertain.
Chances of precipitation will increase for these areas, though
the nature of the rainfall is somewhat uncertain. Generally, a
strong-enough shortwave would lead to increased cloud cover,
cooler temperatures, and stratiform rain. However, some of the
high resolution model guidance indicates that the shortwave
weakens, allowing it to lose some of the thicker cloud cover and
instead promote more showery precipitation. This alternative
solution would mean more sunshine and warmer temperatures stick
around.

Sunday night, another (stronger) easterly wave tracks in from
Yukon, bringing another round of stratiform rainfall to much of
the Copper River Basin on Monday. There is some uncertainty in
the track of this second wave, based primarily on the evolution
of a weak ridge that begins to build over the western half of
Southcentral. The ridge looks to prevent further westward
progression of the shortwave, keeping the bulk of the precipitation
over the Copper Basin through Tuesday, but it can be difficult
for models to resolve the strength and location of weak features
such as this one several days in advance. As a result, some
solutions place the ridge further west, and allow for wetter
conditions to nudge west toward Anchorage, the Mat-Su Valleys,
and the Kenai Peninsula by Tuesday. Regardless of the eventual
solution, expect continued generally cool and cloudy weather with
the occasional break of sun as well as the occasional shower.

- Quesada
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&&


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

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An upper-level trough remains over the Bering this afternoon
currently stretched from the northern Bering into the Gulf. This
feature will weaken overnight as an area of high pressure builds
across the central Bering through Sunday. Shower activity will
decrease this afternoon, however, with increased solar heating
models are hinting at some instability developing in the late
afternoon and early evening hours Saturday and Sunday.

With the departure of the upper low over Southwest, weak northerly
flow will become more prominent the next couple of days. Sunday
sees the arrival of a front into the Western and Central Aleutians,
which will increase wind and showers over the western half of the
Aleutian Chain. The front weakens late Monday as it reaches the
Eastern Aleutians, but scattered shower activity will likely
persist for portions of the southern Bering. New shortwave
activity along the front may reinvigorate winds and showers as the
front moves into Southwest Alaska Tuesday morning.
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&&

.LONG TERM FORECAST (Days 4 through 7) Wednesday through Saturday...

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Ridging over mainland Alaska on Wednesday will help clear skies up
over Southcentral during the day. The calmer weather will be short
lived however as energy from an upper-level trough in the eastern
Bering surges eastward and pushes the ridge to the north. This
pattern change will re-introduce widespread cloud cover and
chances for precipitation across the region as the system
progresses. The trough will dive further south and east into the
North Pacific by Thursday afternoon before the upper-low migrates
northward into the Gulf and towards Prince William Sound by
Saturday afternoon.

Another upper-low will start to form near the western Aleutians
late Thursday and move eastward through Saturday, providing a
chance for precipitation across the Aleutians and Bering. The
positioning of this low and the one in the central Gulf by
Saturday is still undetermined. Some model guidance is suggesting
that they will interact and even start to merge near the Alaska
Peninsula, while other models keep both systems separate from each
other. This would result in the Gulf low remaining closer to
Prince William Sound and the western low positioning itself near
the central Aleutians. In either scenario, broader troughing will
persist over most of the forecast area, producing cooler and
unsettled weather through at least the start of next weekend.

-BS
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&&

.AVIATION...

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PANC...Relatively higher pressure along the North Gulf coast
between a low in the Gulf and a weak thermal trough over interior
Southcentral will lead to development of a week Turnagain Arm jet
this evening. Exact timing is uncertain, but do expect a little
bit of south-southeasterly wind to bend into the terminal.
Earliest arrival would be around 02Z while latest arrival would
be around 06Z. This jet will die down with cooling overnight,
with a switch back to West-Northwest Sunday morning.

VFR conditions will prevail, with showers to the north dieing off
as they track southward into drier more stable air over Cook
Inlet. An upper level short-wave will approach from the east
Sunday afternoon, but will be in a weakening state. There is
potential for ceilings to lower to low end VFR during the day
Sunday, with some light rain or showers possible.
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&&

$$