Small Craft Advisory 409, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
459 AM AKDT Wed May 18 2022

.ANALYSIS AND UPPER LEVELS...

High pressure remains over the Bering this morning juxtaposed to
a continued area of low pressure over the southern Gulf of Alaska.
In between these features a weak pressure gradient is promoting
mild northerly flow at the surface over Southwest. Little to no
cold air advection is limiting any chances for stronger winds.
Over the Bering low stratus and areas of fog have cleared somewhat
offshore of the Kuskokwim Delta and Bristol Bay. Further west,
however, the layer of stratus is persisting from the Western and
Central Aleutians northward across the Pribilofs and over Saint
Matthew Island. Some soupiness continues to impact the Bering side
of the Alaska Peninsula and Eastern Aleutians with locations like
Dutch Harbor and Cold Bay experiencing lowered ceilings to IFR
levels. Interior Alaska is fairing much better with dry and
clear conditions across the majority of Southwest. What remains of
an easterly wave through Prince William Sound is dipping southward
and into the Gulf. The result is an axis of cloudiness extending
from near Gulkana southward into Prince William Sound and over the
Turnagain Arm. Light shower activity does continue over the higher
elevations and for Valdez.

&&

.MODEL DISCUSSION...

Models continue to come into better synoptic agreement with only
minor differences overall. While high pressure will be the main
story across both Southwest and Southcentral the next couple of
days, the next low pressure system will bring a front into the
Aleutian Chain on Thursday. Global models and even the higher res
guidance are all in harmony with each other.

&&

.AVIATION...
PANC...VFR conditions and light winds continue on Wednesday and
are expected to persist into Thursday.

&&

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

The upper level wave that brought rain to Prince William Sound
and the Copper River Basin (and snow through some of the passes)
yesterday and overnight is weakening and moving south this
morning. There are some areas of light precipitation through the
middle of Prince William Sound but it will end this morning. As
high pressure builds in from the west, Southcentral will see a
warming and drying trend the next few days. Winds will overall
remain light with afternoon and evening seabreezes developing
along the coast.

The next system will be a front that will move over Kodiak from
the south on Friday. This will bring rain to Kodiak at that time,
but the front will stall and have difficulty moving northward due
to the ridge over Southcentral. This is the biggest weather
question at this time: Will the front break down the ridge after
Friday or will the front weaken in place and dissipate due to the
strength of the ridge? That will determine the weather for this
coming weekend over Southcentral.

&&

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

Clear and dry conditions continue as high pressure tracks
northeastward out of the Bering over the Mainland. Winds have come
down over much of the region and will remain so through Friday
morning. Flow then shifts east-southeasterly with the approach of
a front extending off a North Pacific low that pushes over the
AKPen and Bristol Bay late Friday morning, and will gradually
increase into the overnight hours. There is a chance for
precipitation along the front as well across the AKPen and parts
of Bristol Bay Friday night, but may end up being confined to the
upslope areas of the mountain ranges. Additionally, temperatures
will continue to rise to the mid to upper 60's across Southwest
Thursday and Friday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

Areas of low stratus and fog sit over the central Bering and north
of the AKPen under the ridge of high pressure. A trough extending
out of Russia and over the Western Aleutians and a North Pacific
low pushes the high pressure northeast towards the Southern
Mainland. The front extending off the North Pacific low moves of
the Eastern Aleutians Thursday afternoon, bringing widespread
small craft winds, with an areas of gales on the Pacific side
overnight Thursday, and rain showers.

&&

.MARINE (Days 3 through 5: Friday through Sunday)...

Gulf of Alaska: The Gulf high weakens as it moves over North Gulf
Coast for Sat. Front enters Southern Gulf Sun. North Pacific low
moves to the East of Sitkinak for Sun. Forecast confidence is
fair. Gusty Easterly winds increase to high end gales with the
front through Sun. Gales spread through Shelikof Strait for Sat,
through the Barren Islands and Kamishak bay by Sun. Seas build to
16 ft East of Kodiak for Sat subsiding Sun.

Bering Sea: A 995 mb North Pacific low remains South of the
Aleutians spreading gusty easterly winds across the Bering
through Sun. Confidence starts good but decreases by Sun.
Widespread gusty easterly winds spreading over Bering increasing
to high end gales by Sun. Highest winds over the Aleutians. Seas
building to 16 ft Friday Pacific side of the Aleutians spreading
East through Sun. Seas to 12 ft Bering side of Aleutians through
Fri.

&&

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

Established ridging over southern mainland Alaska will keep high
temperatures in the 60s for much of the region through the
weekend. This will enhance snowmelt and subsequent flooding
concerns, especially in the Copper River Basin where snow water
equivalent has been at or near all-time highs in many locations.
In places that are already snow-free, the drier and warmer weather
will help to dry out fuels and increase fire danger, though winds
are expected to remain relatively light under the influence of
high pressure. Further south and west, a series of low pressure
systems in the North Pacific brings more unsettled weather this
weekend from the central Aleutians to the AKPEN and Kodiak Island.
Wetter, windier conditions can be expected as a front extending
across the AKPEN and Kodiak Island pushes slowly northward,
leading to enhanced rainfall and gusty easterly winds.

Forecast uncertainty increases into early next week as models
disagree on how far north this front will reach, with GFS rapidly
weakening the ridge over the mainland on Sunday, allowing the
front to push into the southern mainland. As a result, there is
some chance Southwest Alaska may see windier conditions, with rain
showers and stronger winds also possible along the north Gulf
coast. Other models, however, indicate a more robust ridge keeping
the North Pacific lows at bay. In general, ridging looks to trend
back over the Bering Sea by Monday, allowing weak troughing to
develop over Southcentral. With the potential for shortwaves to
dig southward from the Arctic with weak disturbances lingering in
the Gulf, a return of more unsettled weather and chances of rain
can be expected for the beginning of the week. Southwest Alaska
may benefit from the presence of the ridge for a little longer as
the ridge recedes westward before chances of showers increase on
Tuesday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Advisory 141.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KM
MARINE/LONG TERM...CL/CQ