000
FXAK68 PAFC 240023
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
423 PM AKDT Sat Sep 23 2023

.ANALYSIS AND UPPER LEVELS...

An occluded low near St. Matthew Island continues to weaken as it
drifts southeast towards Bristol Bay, though bringing gusty
northwest winds from St. Paul Island south into the Aleutian
chain. Cloudy, but otherwise benign, conditions continue for much
of southwest and southcentral Alaska with an upper-level ridge in
place. Meanwhile, a weakening low remains in place across the
northern Gulf of Alaska. Showers were observed moving westward
along the southern Prince William Sound and Kenai Peninsula on the
northern periphery of the Gulf low.

&&

.MODEL DISCUSSION...

Models remain in very good agreement over the next several days with
only small discrepancies on the mesoscale. For that matter, the
NAM was the preferred model. Model spread increases significantly
after Thursday of next week, especially with regards to the
evolution of a low in the eastern Bering.

&&

.AVIATION...
PANC...VFR will prevail through the TAF period with light wind.
Cannot rule out an isolated shower given available moisture and
some instability on the northern periphery of the low in the Gulf,
but confidence and coverage is low enough such to preclude
mention in the TAF package.

&&

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

Mild weather is expected this forecast period. On satellite
imagery there is a broad area of weak low pressure over the
Gulf of Alaska, with low to mid-deck clouds associated with this
circulation and isolated showers. This low will linger and
continue to decay. The jet is well west of the region (over the
Aleutians specifically), and will stay out of Southcentral
through Tuesday. For Anchorage and the Mat-Su valleys afternoon
temperatures will reach the 50s the next 3 days with lows staying
above freezing. Some locations, especially in the Copper River
Basin, will dip below freezing Sunday, Monday and Tuesday
mornings. Tuesday morning the models bring a 975 mb to 977 mb low
near the panhandle which will bring and inverted trough to the
northern Gulf and Prince William Sound. This low is actively being
monitored.

&&

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

Weak showers across the Kuskokwim Delta are slowly weakening and
will despite into this evening. As expected, weak showers farther
south struggled to make it inland, and if they did, were
incredibly light. The parent low that is spawning this weather is
also weakening and will get absorbed into the upper level flow
tomorrow morning. Overnight clouds and highly scattered showers
may skirt the coast this overnight, but overall weak surface winds
will keep temperatures from dropping much overnight.

Sunday will see showers increasing across the western Bering as
two different low pressure systems drift east. Generally
higher pressure across inland Southwest is expected to keep
conditions drier through the rest of the weekend and into the
start of the week. Precipitation spreads eastward throughout the
day and reaches the eastern Aleutians by Sunday night, the AKPEN
by Monday morning, and then precipitation exits into the North
Pacific in the afternoon. Sustained winds are advertised to remain
at or below small craft. High pressure spreads across the Bering
for the remainder of Monday, helping to keep conditions generally
drier.

&&

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

Models begin in good agreement that weak troughing will extend
across mainland Alaska into the Gulf of Alaska on Wednesday. The
weak cyclonic flow accompanying this feature may allow for partly
to mostly sunny skies and the development of isolated to
scattered showers across southern mainland Alaska, particularly
along the east side of the trough axis over Southcentral. This
feature lifts north and east out of the area through Thursday with
good confidence.

Upstream, there is less agreement on the track of a broad,
occluded low over the Bering Sea, with model solutions depicting
various degrees of eastward progression. Broadly speaking, this
low looks likely to bring rain along the Southwest coast Wednesday
night into Thursday. After this, confidence rapidly decreases as
model solutions diverge. During the Thursday and Friday timeframe,
GFS and GEM suggest that a low enters or develops in the Gulf of
Alaska. As a result, chances for rain increase toward late week
along the Gulf coast, with some potential for offshore winds
through gaps along the coast as well. Then, models come somewhat
back into alignment with a large, stronger low (likely at least
gale force) pushing its front across the Aleutians on Friday.
However, the north and eastward progression of this low is highly
uncertain with models suggesting a wide spread in forward motion.
The general trend in the pattern suggests increasing chances of
widespread, steady rainfall going into the weekend. However, until
the very uncertain timing of the arrival of the front, pleasant,
relatively dry weather looks to continue for southern mainland
Alaska.

&&
$$