Small Craft Advisory 347, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
444 PM AKDT Sat Apr 23 2022

.ANALYSIS AND UPPER LEVELS...

A broad vertically stacked low continues to spin over the Gulf
while gradually tracking eastward. Precipitation associated with
an occluded front continues along the northern Gulf coast but is
quickly dissipating. Farther west, an upper level ridge builds
over the central Bering while a short wave trough extends
southward along the Kuskokwim Delta Coast. A front associated with
a Kamchatka low extends over the western Aleutians, introducing
gusty southerly winds and rain.

&&

.MODEL DISCUSSION...

Model solutions are in good synoptic agreement through the short
term. The biggest challenge with this forecast is the timing of
upper level shortwaves rotating around the Gulf low, which could
produce showery activity over Southcentral through early Sunday. By
late Sunday, there is some uncertainty regarding the upper level
shortwave over Southwest and how far south it will move over the
mainland Monday morning. Meanwhile, there is good agreement that
the current Kamchatka low will send a weakening front across the
Bering through late Monday. By Tuesday, there is good agreement on
the development of a North Pacific low tracking across the
western Aleutians and into the western Bering. Currently models
are hinting at gale force winds associated with this low, with the
potential for storm force winds, though confidence remains low.

&&

.AVIATION...
PANC...VFR conditions will persist through the TAF period. The
weak Turnagain Arm wind will will be brief, diminishing by late
evening.

&&

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

On satellite imagery there is a broad area of cyclonic
circulation over Southcentral and the Gulf Of Alaska. At the
surface there is a 995 mb low approximately 350 nm southeast of
Kodiak which will continue to weaken and slowly move towards
Southeast Alaska. The remnants of the occluded front will linger
over the Gulf this forecast period. Temperatures will range from
the upper 40s to low 50s in the Anchorage Bowl and the Mat-Su
valleys the next few afternoons.

&&

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

Relatively quiet weather is ahead for Southwest Alaska. Cloudy
skies will continue through Sunday as a vertically stacked low
lingers in the Gulf. From tonight through Tuesday, a robust upper
level shortwave will make its way across Southwest and into the
Gulf. Lows will drop into the high 20s and low 30s with this
shortwave, while highs will be in the 40s. Colder air aloft in
conjunction with favorable dynamics will increase the chance of
snow and rain showers. Parts of the Kuskokwim Delta may see
showers beginning Sunday morning, with precipitation favored near
west-facing slopes. Along with the upper level shortwave, the
showers will track east across the Lower Kuskokwim Valley and
northern Bristol Bay, reaching the Alaska Range by Monday. A ridge
pushes into the Southwest coast behind this shortwave, and clouds
begin to diminish late on Sunday. A front approaches from the
Bering, though it looks to dissipate before it reaches Southwest
Alaska. As such, expect light winds and low precipitation
likelihood to persist through Tuesday.

&&

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

A ridge over the Central Aleutians and Bering will continue
moving eastward, bringing calm weather across the Eastern
Aleutians through Tuesday morning. Further west, a strengthening
surface low pushes its front across the Aleutian Chain, bringing
gales and rain to the Western and Central Aleutians through late
Monday. Another surface low pushes into the Bering from the North
Pacific on Monday night. Models are trending towards storm-force
winds with this low, though some uncertainty remains with its
track.

&&.MARINE (Days 3 through 5: Tuesday through Thursday)...

Gulf of Alaska - Expect winds less than 25 kts and seas less than
8 ft.

Bering - An active pattern is expected across the Bering/Aleutians
during the timeframe from Tuesday to Thursday. Model guidance is
locking in on a strong and compact low moving into the Western
Aleutians/western Bering on Tuesday. Expect an area of high end
gale force winds especially for the southwestern Bering including
the Western and Central Aleutians with widespread small crafts.
Seas building 15 to 20 ft on Tuesday, subsiding Tuesday
night/early Wednesday. There is the potential for a small area of
low end storm force winds as well though this is more uncertain at
this time. This low then gets deflected back to the southeast
towards the North Pacific while weakening Wednesday. Wednesday
through Thursday, model guidance is showing another rather large
and elongated gale force storm system encompassing much of the
Bering. This low will be moving eastward from the Kamchatka
Peninsula. Seas building across the western Bering 15 to 20 ft
Thursday. Moderate confidence at this time for the
Wednesday/Thursday timeframe.

&&

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

The long term forecast starts late Wednesday with a highly
amplified pattern consisting of a deep upper-level trough over
the western Bering and a second, more complex, trough centered
near the Al-Can border. Between the two, an upper-level ridge
extends from the north Pacific to the Chukchi Sea. This highly
amplified pattern is also quite active and complex, with each
trough dominated by a pair of upper-level lows. The Bering trough
is associated with a surface low over the western Aleutians and
front extending across the eastern Aleutians. These features
weaken and drop southeastward through Thursday only to be
replaced by a second Kamchatka low moving toward the Chain. The
low stalls and weakens through Friday, running up against the
ridge downstream, as its front moves to the eastern Aleutians.
Models then drastically diverge for Friday, with the EC keeping
the low nearly stationary over the southwestern Bering and the GFS
developing a new low along the front and sliding it underneath
the ridge to the western Gulf. Either way, conditions will remain
unsettled along the ALeutians and AKPen. However, the extent of
gusty winds and precipitation across the Bering and Southwest
coast is highly uncertain.

For the Mainland, the extent of clouds and diurnal shower activity
will be the biggest challenge to the long term forecast, as much
of Southcentral and interior Southwest Alaska remain under the
influence of the upper-level through. An upper-level wave ejecting
from a low over interior western Alaska will increase the chance
for showers Wednesday afternoon and evening. Guidance then
indicates the potential for the interior system to pull a second
shortwave over the Gulf northward for Thursday. This solution
could keep precipitation along the coast and further increase
chances for showers over the interior of the Southern Mainland.
Again, models diverge by Friday, as the EC keeps the upper-level
low over in the interior in place with persistent shower activity.
The GFS, however, lifts this feature northwest and tries to build
a ridge across Southcentral as an upper-level wave lifts into the
Gulf (due to the elongation of the aforementioned Bering low and
development of new low along the front). With the interior trough
moving north, the GFS hints as less shower activity by the weekend
across Southcentral. Temperatures through the long term are
expected to remain seasonable along the coast and above average
across interior locations.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale 175 177 178.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KO
SOUTHCENTRAL ALASKA...PJS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KC
MARINE/LONG TERM...TM