Small Craft Advisory 938, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
432 PM AKST Thu Nov 24 2022

.ANALYSIS AND UPPER LEVELS...

A negatively tilted through extending southeastward across
Southcentral is bringing active weather to the region in short-term.
Associated precipitation tracking across the western Gulf will
move onshore this evening. More zonal flow is seen across
Southwest Alaska leading to drier conditions and partly cloudy
skies. A weak ridge is bringing benign conditions to much of the
Bering, with slightly stronger northwesterly winds south of the
AKPEN between these large scale features.

&&

.MODEL DISCUSSION...

The GFS remains a significant outlier with regards to a low
developing and tracking through the Gulf late tonight into Friday.
Its position allows for a band of snow to continue through Friday
evening and thus would bring much higher totals to Anchorage and
the Mat-Su. All other models bring an initial shot of snow to the
area late tonight into early Friday before quickly ending. This
is the preferred solution at this time. Source layer temperatures
are near -15C. As such, lighter, more fluffy snow may yield to
slightly higher totals but much lower overall than the GFS
solution.

&&

.AVIATION...

VFR ceilings will lower to MVFR this evening as snow moves into
the region. Brief IFR visibilities are possible during heavier
periods of snow. VFR conditions will return by Friday afternoon.
Light winds will persist.

&&

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

A shallow, negatively-tilted, upper-level trough continues
extending into Southcentral from the west and will bring a quick
round of light, widespread snow to Southcentral. Snowfall is
expected to begin for the Anchorage area and Mat-Su Valleys this
evening and then taper off through Friday morning as wind
generally shifts westerly and drier air moves in. The Copper
River Basin can expect to see the bulk of the snowfall on Friday
morning. Snow is expected to linger along coastal Prince William
Sound locations (Valdez and Cordova) through Friday night due to a
surface low that develops over the Gulf. Overall with this
system, the greatest snow amounts are advertised for the Hatcher
Pass area, Paxson area, and northeast Prince William Sound. The
aforementioned low will continue exiting to the southeast while
high pressure builds over the Mainland. As a result, precipitation
across Southcentral clears by Saturday and gusty northerly
offshore winds develop along northern Gulf coast, especially
through areas of channeled terrain like Thompson Pass. Cold, dry,
and clear conditions are expected to persist through the end of
the weekend.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Tonight
through Sunday)...

Precipitation will taper off this evening across all of Southwest
as a front progresses into the western Gulf. A ridge of high
pressure then builds over the Bering which will result in cool
northwesterly flow making its way back into the region. The return
of a colder air mass should help bring temperatures back down
into the 20s for highs and 0s to 10s for lows for both Friday and
Saturday. Any new snowfall through the end of the week should stay
generally confined to areas favored for upslope flow along the
Kuskokwim Mountains and Aleutian/Alaska Ranges. One exception will
pertain to a small, fast-moving shortwave that will move
southeast on Friday between the Kuskokwim Delta and Bristol Bay. A
quick flurry of snow showers will likely follow this system as it
tracks through, with the best chance for light snow over southern
portions of Bristol Bay and the Kuskokwim Delta for Friday
afternoon. Otherwise, expect cool and quiet conditions to persist
across the region through Sunday morning.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3:
Tonight through Sunday)...

A brief lull in the pattern is expected for most of Friday into
Friday night as a broad upper-level ridge expands across the
Bering. Westerly small craft winds near Saint Matthew Island and
occasional snow showers moving into the Pribilofs are forecasted
for Friday. On Saturday, the ridge axis will begin to shift east
as a North Pacific low approaches the western Aleutians. Winds
will pick up from the east and rain will begin as the low's front
approaches on Saturday morning across western parts of the Chain.
Rain will spread east out to Atka and Dutch harbor by Saturday
evening as the low crosses into the western Bering. Easterly gale
force to winds will shift into the central Aleutians through
Saturday evening and track northeastward before exiting the
northern Bering early next week.

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

The key feature in the long term is a building ridge over the
mainland, creating a highly amplified pattern for next week. By
Monday afternoon, an upper level trough over the Alaska-Yukon
border will be departing eastward. As an upper level ridge to the
west builds in, gusty outflow winds, particularly along the
northern Gulf coast, will be the main concern for much of Monday
into Tuesday. By Tuesday morning, an upper level shortwave
dropping southward will likely enhance the northerly winds for a
brief period. As the ridge builds over the mainland Wednesday,
generally quiet conditions are expected for Southcentral.
Meanwhile attention shifts to Southwest and the Alaska Peninsula
as models are all hinting at the arrival of a shortwave trough
Wednesday into Thursday. While confidence is low due to lack of
model agreement, this feature does have the potential to introduce
onshore flow and increase chances of precipitation for the end of
the week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 119 120 130 131 150 155 176-178 185 351 352.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AP
SOUTHCENTRAL ALASKA...AF
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...NS
LONG TERM...KO