Small Craft Advisory 232, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
513 PM AKDT Sat Mar 18 2023

.ANALYSIS AND UPPER LEVELS...

The main weather feature is a strong low pressure system tracking
through the Gulf of Alaska from southeast to northwest. Radar
shows moderate and heavy precipitation across Prince William Sound
and the Kenai Peninsula. Gusty, easterly winds are also
strengthening as a result of a tightening pressure gradient
between a mainland high and Gulf low. Out west, a low centered
along the Alaska Peninsula is bringing northerly winds and light
snow showers over the eastern Aleutians and Bristol Bay coast. A
weak front is pushing into the Bering Sea, while a deep low in the
North Pacific approaches the western Aleutians.

&&

.MODEL DISCUSSION...

Model guidance is in decent agreement with the placement and
intensity of synoptic scale features at both the surface and in
the upper levels. The current forecast is on track for heavy snow
and gusty winds for interior locations of the eastern Kenai
Peninsula today. There is some uncertainty with precipitation type
for coastal and near- coastal areas such as Seward and Portage
Valley due to the timing of the warmer air intrusion.

&&

.AVIATION...
PANC... A chance for light snow this afternoon before changing
over to a rain/snow mix in the evening. Ceiling and visibility
will lower to MVFR conditions, with increased northerly winds.
Conditions are expected improve through the overnight hours, with
increasing winds out of the south.

&&

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

The second of two very similar east-to-west tracking lows is now
making its approach on the Kenai Peninsula this afternoon.
Widespread moderate to heavy snowfall has overspread much of the
Kenai Peninsula on schedule to the north of the center as a deep
stream of moisture fires into the Prince William Sound region.
Most of the heaviest rates have been observed over the Portage
Valley and Whittier so far, although a developing east wind will
help push temperatures above freezing and result in mixing with or
changeover to rain at lower elevations between Whittier and the
Turnagain Arm this evening. Farther west, it's looking more likely
downsloping associated with developing cross- barrier flow north
of the low as it moves quickly towards the Barren Islands will end
up limiting snowfall totals, with the best chance for a few
inches of accumulating snow focused down towards Homer. Similarly,
downslope drying will be a limiting factor over the Mat Valley
and Anchorage area, with the best potential for accumulating wet
snow focused over the upper hillside through this evening. A
Winter Weather Advisory and Winter Storm Warning remain in effect
for the western and eastern Kenai Peninsula respectively for the
combination of falling and blowing snow this evening.

By early Sunday, the rapidly west-bound low will move out of the
picture as it heads out over Bristol Bay, with a colder air mass
expected to be pulled into Southcentral as it wraps in from the
Gulf behind the low. This will leave much of the region in a
showery, onshore flow pattern, with lingering snow showers focused
primarily along the coast between the western Prince William Sound
and eastern Kenai Peninsula. The upper level low in the southwest
Gulf will stretch out into an upper trough that will lift
northeast across Southcentral late Sunday into Monday, but drier
air in place by this point will prevent this system from spurring
off any renewed precipitation for most of Southcentral. A front
associated with a large low moving over the Bering will reach
Kodiak Island by Monday afternoon, then continue north into the
Kenai Peninsula as a triple-point low attempts to form along it
and move towards Prince William Sound. This will bring in our next
potential for light snowfall shifting from Kodiak Island on
Monday and up towards the Kenai Peninsula once again by Tuesday.

&&

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

Remnants of a Gulf low are now tracking into interior Bristol Bay
this evening with increasing cloud cover and somewhat elevated
northwesterly winds of 15 to 20 mph. Saturday started off with
largely clear skies across Southwest and pleasant conditions
through the afternoon hours. Through tonight, however, clouds will
continue to spread westward, eventually encompassing all of
Southwest. A winter weather advisory remains in effect later
tonight for expected blowing snow through the early morning hours
on Sunday across interior Bristol Bay. Light snow with
accumulations of 1 to 2 inches are forecast from Dillingham and
northward. Increasing winds with gusts to 40 mph will promote
reduced visibility down to one half mile at times due to blowing
snow. This will be the primary concern through Sunday. By Monday a
strong Bering front is forecast to overspread the Kuskokwim coast
with enhanced southeasterly winds and renewed snow showers. While
accumulations will likely be light, winds gusting to as high as
50 mph will promote a threat for blowing snow and reduced
visibility from Nunivak Island to the Kuskokwim coast through the
morning hours on Monday. Impacts could potentially spread further
inland as well, though some uncertainty remains in the finer
details. Thus, a high wind watch is in effect for the region
Sunday morning, which will be fine tuned over the next 24 hours.

A low centered along the Alaska Peninsula will slowly track out
into the north Pacific today before a second system moves into
Southwest Alaska tonight. The vertically tilted first low extends
its influence northward across Bristol Bay this morning, with
light snow showers ongoing along the coast. These will diminish in
intensity through the morning as the low exits southward slowly,
leaving partly cloudy skies in its wake. Solar heating will bring
high temperatures into the 20s and 30s for much of the region.

&&

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

The Bering Sea remains wedged between a broad trough over the
Gulf of Alaska and the next North Pacific low on its way to the
Western Aleutians. A high wind warning has been issued for the
Western Aleutians in anticipation of winds gusting up to 85 mph.
Strong cold air advection wrapping around the deepening low will
support continued strengthening through the morning hours on
Sunday. This should coincide with the low's passage over the
Western Aleutians. Hurricane force southwesterly winds will
precede the low followed by another round of hurricane force
southwesterly winds behind the low as it lifts northward into the
western Bering. Widespread high wind gusts are likely with the
low's passage and resultant seas could build to as high as 40
feet. The Bering low is then forecast to continue across the
central Bering through Monday. Its front will traverse the Central
and Eastern Aleutians Sunday night through Monday afternoon,
reaching the Alaska Peninsula and Southwest Alaska by Monday
evening. All in all, an unsettled weather pattern is forecast
through early next week and widespread gales, storm force winds,
as well as elevated seas, are expected to encompass much of the
Bering late Sunday into Monday. Tuesday will see conditions begin
to relax somewhat, but models are hinting at a Kamchatka low
dropping southward into the western Bering late Tuesday afternoon.

&&

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

Active weather looks to continue through the Gulf of Alaska and
coastal Southcentral Alaska through the long-term period. A deep
negatively tilted trough extends southeastward from Siberia,
through Southwest Alaska and the Alaska Peninsula, and into the
North Pacific. Guidance is still in disagreement with strength and
positioning regarding the resultant surface low in the Gulf. The
12z GFS is the strongest of the guidance and the most south with
positioning in the extreme southwestern Gulf on Wednesday. The 12z
Canadian is a middle-ground between the stronger GFS and the
weaker 12z ECMWF. the Canadian and ECMWF guidance have the low in
the vicinity of Kodiak Island. Regardless, it appears that Kodiak
Island, as well as the eastern Kenai Peninsula, Prince William
Sound, and the northern Gulf Coast will see the best chance at
amplified precipitation both from the direct influence of the low
and from its front as it moves north to coast Wednesday through
Thursday. Gale-force winds with potentially storm-force gusts will
be a good bet for the southwestern to south-central Gulf as the
system pulls away to the east Thursday. Another shortwave looks to
approach Southcentral and the Gulf from northwest Friday into
Saturday. However, confidence during this timeframe is extremely
low due to many disagreements in strength and positioning/track of
a potential low pressure system that could develop in the
vicinity of Prince William Sound Friday. However, with north to
northwesterly flow over Southcentral as the upper trough axis
moves into the Gulf, a turn to a colder and potentially drier
pattern could take shape for the beginning of the weekend.

Out west, conditions look to remain unsettled for interior
locations of Southwest Alaska Wednesday as the area contends with
weak shortwaves pivoting back to the west from the upper low in
the Gulf. Meanwhile, another shortwave looks to dig southward from
the from the northern Bering Sea and cause a weak low pressure to
spin up near the Southwest coast/eastern Bering Thursday bringing
another chance at precipitation for coastal locations in the
morning and working into interior Southwest during the evening and
overnight Thursday. Conditions then quiet down for Friday and
Saturday.

The western and central Bering Sea/Aleutian Chain remain relatively
benign in the weather department for most of the long-term period
while the eastern Bering/Aleutian Chain contends with continued
gusty northerly flow through Thursday. However, there is some
uncertainty and questions whether a storm will form in the North
Pacific Wednesday evening; and if it forms, how far north does it
make it. The GFS is the most aggressive with the warm front
skirting the central and eastern Aleutian Chain Thursday and
Friday. Meanwhile, other guidance does not show a storm forming at
all. Guidance is beginning to key in on a Kamchatka low sending
its front eastward towards the western Bering/Aleutian Chain
Friday into Saturday. This will provide increased chances at
precipitation and gusty conditions. Winds look to be only gales at
this time.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Storm Warning: 125.
         Winter Storm Watch: 155.
         Winter Weather Advisory: 121 161.
         High Wind Warning: 191.
MARINE...Hurricane Force Wind Warning: Central and Western Aleutians.
         Storm Warning: Northern Gulf of Alaska, Central Aleutians,
         Pribilofs.
         Gale Warning: Prince William Sound, Passage Canal,
         Barren Islands, Western Gulf of Alaska, Cook Inlet,
         Eastern Aleutians, Kuskokwim Delta Coast, Saint Matthew Island.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MF
SOUTHCENTRAL ALASKA...AS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BL
LONG TERM...DAN