Brisk Wind Advisory 5, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
528 PM AKST Sat Jan 14 2023

.ANALYSIS AND UPPER LEVELS...

A long-wave trough remains firmly entrenched across Alaska, with
a host of mostly weak lows and short-waves. An east-west oriented
short-wave is lifting northward across the Gulf of Alaska and
Bristol Bay, with numerous embedded vorticity maxima embedded in
the flow out ahead of it. Radar imagery shows widespread steady
light precipitation across Prince William Sound, the Gulf coast
and from Bristol Bay up to the Kuskokwim Delta coast. Some
precipitation is spreading inland across Southcentral as well.
Precipitation-type is a mixed bag, with snow transition to rain
for areas near sea level along the Gulf coast and eastern Kenai
Peninsula, a mix of rain and snow along the Alaska Peninsula,
and all snow as you head to Dillingham and areas to the north
and west. Warmer air has spread over the coastal mountains of
Southcentral as indicated by the temperature inversion in the
Anchorage sounding. It is a borderline freezing rain sounding
which introduces complexity into the precipitation-type forecast.

Out west, a seemingly ever-present weak low complex remains parked
along the central to western Aleutian chain. This is leading to a
showery pattern across the Bering and Aleutians along with fairly
light winds as well. Lastly, satellite imagery shows a gale force
occluding low tracking northward out of the North Pacific toward
Kodiak Island and the Alaska Peninsula. There are indications of
a weak triple point low east of the main center, though this does
not seem to be developing any further.

&&

.MODEL DISCUSSION...

Models are in fair agreement with large scale features through
Monday. There are then minor differences in position with a low
tracking from the eastern Gulf to northern Gulf Monday
night/Tuesday. The precipitation forecast for Southcentral Alaska
remains the biggest forecast challenge for tonight through Sunday.
Uncertainty in the precipitation type from the western Kenai
Peninsula to Anchorage is particularly high due to a borderline
snow-freezing rain scenario, where precipitation intensity could
make all the difference.

&&

.AVIATION...
PANC...Expect periods of light precipitation this afternoon and
evening, which may lower the ceiling/vis down to MVFR at times.
The predominant precipitation type is expected to be snow, though
there is a chance for freezing rain as well. Very light
precipitation will remain in the vicinity through Sunday morning,
but after the first round of precipitation this afternoon/evening,
a slight increase in southeast flow coming across the Kenai and
Chugach Mountains will likely be enough to maintain VFR
conditions.

&&

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

An upper-level ridge is currently lifting north into the
central/northern Mainland while a negatively tilted long-wave
trough follows in tow. Weak, disorganized, and light precipitation
continues moving onshore as an east-west oriented shortwave lifts
northward across Kodiak Island and heads towards Southcentral for
tonight. As such, snow will continue transitioning to rain for
areas near sea level along the eastern Kenai Peninsula and the
Gulf coast, and mostly light snow can be expected to for the
western Kenai Peninsula and Anchorage area. Periods of light
freezing rain may be possible for the latter areas as warm air
continues to advect over the coastal mountains.

By Sunday morning, precipitation should lighten behind the
shortwave as it exits to the north. However, precipitation along
the Southcentral coast will generally continue into early next
week as a North Pacific low tracks south of Kodiak Island on
Sunday and then weakens moving into Bristol Bay on Monday. The
low's front will lift across Kodiak Island later on Sunday morning
(introducing rain, once again), the southern Kenai Peninsula on
Sunday afternoon, and then the Prince William Sound area by Sunday
night/Monday morning. Areas near sea level along the immediate
Southcentral coast should stay mostly rain with a wet mix of rain
and snow possible. Another system is advertised to track into the
Gulf on Tuesday, however there is lower confidence with this
feature since models cannot yet agree on its track and intensity.

&&

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

A low located in the Bering continues to spin in place with
multiple shortwaves embedded within and rotating around the low's
center. The occluded front associated with this system will
continue to bring light snow showers into Bristol Bay and advance
northward along the Kuskokwim Delta Coast through tonight.
Accumulations with this frontal passage will remain light.
Temperatures have warmed slightly above freezing across the
northern Alaska Peninsula (AKPen), resulting in mainly rain
falling near the coast. This trend of rain along the AKPen will
continue and will spread northward into the eastern portions of
Bristol Bay as a low tracks across the Peninsula Sunday into
Sunday night. Simultaneously, overall winds will increase for the
forecast area, especially the Kamishak gap and the Kuskokwim
Delta. Heading into the beginning of the week, temperatures will
trend warmer along the coast and Bristol Bay, while the Kuskokwim
Valley and inland areas of the Kuskokwim Delta will remain cooler.

&&

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

A decaying, vertically stacked low continues to spin in place
over the western Bering Sea and Aleutians, with several shortwaves
embedded within and rotating around the low's center. Most of the
Bering remains in a showery and unimpactful pattern under the
influence of the aforementioned weakening low, with winds
generally small craft criteria or less along the Aleutian Chain. A
low will track across the Alaska Peninsula (AKPen) Sunday and
will aide in bringing northerly small craft winds across the
northern Bering as colder air is dragged southward. Overall, an
unsettled weather pattern will continue across the
Bering/Aleutians throughout the forecast period.

&&

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

Looking ahead in the extended forecast, the latest model runs and
ensemble guidance are in decent agreement with the evolution and
progression of the synoptic features. After a remnant low weakens
over the Gulf on Wednesday, a fairly progressive pattern will
ensue across the northern Pacific mid to late next week.

A broad upper trough is positioned over the Bering Sea and
western Alaska, with upper level ridging building across western
Canada. At the surface, a developing low will cross southeastward
towards the western Aleutians between late Wednesday and Thursday.
The general consensus seems to keep the center of the low to the
south of the Chain with a period of small craft winds and snow
showers expected for the region.

A well organized low meanwhile is expected to track northeastward
across the Pacific and likely reach the western and northern Gulf
from Thursday to Saturday. Although the GFS deterministic run is
a little faster in the low track, this storm system will likely
produce moderate to heavy precipitation for coastal Southcentral.
The heaviest precipitation will likely be across Kodiak Island,
the eastern Kenai Peninsula, and Prince William Sound, along with
gusty onshore winds potentially reaching gales.

Most of the southern mainland should remain dry due to
downsloping, but some light snow is possible by late Friday to
early Saturday. Beyond Saturday there is growing confidence for
another stronger system to impact Southcentral.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning: 130
		 Heavy Freezing Spray: 185
FIRE WEATHER...NONE.

&&

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

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