Small Craft Advisory 254, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
443 PM AKDT Sun Mar 25 2018

.ANALYSIS AND UPPER LEVELS...
The upper level ridge over Southcentral Alaska and the Interior
of the state is hanging around and not breaking down as fast as
anticipated in previous days. This has also pushed the developing
triple point low to the southern end of Kodiak Island and will
keep it farther south in the Gulf. The surface low is currently
near the Pribilof Islands and the front associated with it is
slowly moving over Southwest mainland Alaska. The colder air
moving into the central and western Bering Sea and Aleutian
Islands has moderated some from a few days ago when well-defined
convective snow showers were very evident on satellite imagery.

&&

.MODEL DISCUSSION...
It is interesting to look at the changes in the models from
yesterday in the northern Gulf. At that time model consensus was
very good with all four major models coming into good agreement
with the low skirting just south of the Kenai Peninsula and Prince
William Sound. However, model consensus does not necessarily mean
model correctness. Models are all once again in good agreement
with each other, but now track the low south of Middleton Island
which changes the weather picture along the north Gulf coast and
parts of the Southcentral inland areas as well. This is mainly due
to the ridge of high pressure over the state being stronger than
anticipated by the models which is keeping the low track farther
south and slowing the eastward progression of the low in the
eastern Bering Sea between the Pribilof Islands and Kuskokwim
Delta.

&&

.AVIATION...
PANC...VFR conditions and light north winds will persist.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Most of the area will continue to see generally sunny and warm
conditions through Monday as a ridge of high pressure limits the
northward progression of the approaching gale force front into the
Gulf. As a result most of the impacts from this front will be for
widespread rain/snow to Kodiak Island, along with some weak
outflow winds along the Gulf Coast. The associated low will
however slowly fill as it enters the Gulf tomorrow with weakening
high pressure over the mainland, so none of these outflow winds
are expected to be too significant (below gale force) or long-
lived.

By late Monday the ridge of high pressure will lift northward into
the interior, leaving much of the area under southwesterly
cyclonic flow. The exact impacts of this change are still
uncertain however with significant model spread in the placement
of showers. In a nutshell, there is good confidence that the
warm/sunny pattern that much of Southcentral has been in will
begin to break down early this week, but low confidence in the
precipitation forecast. As a result much of the area remains under
slight chance/chance POP's through Tuesday but these will likely
need to be increased/decreased accordingly as forecast confidence
improves.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Snowfall over the mainland will intensify throughout the evening
as the occluded front moves onshore. Easterly flow coming through
Kamishak Gap should keep the blowing snow to a minimum due to
warmer temperatures. Snow will continue through Monday morning,
but rapidly lose intensity during the afternoon hours. From Monday
night onward, the upper low pressure system responsible for the
front will move onshore, bringing some very unstable cold air
aloft with it. Snow showers will be prevalent until the system
passes late Tuesday night.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
As the current low pressure system over the Pribilof Islands moves
eastward, snow showers in northwesterly flow will replace it.
Some light to moderate snow will linger along the front over the
central/eastern Aleutians while slowly moving eastward and
dissipating through Tuesday. Winds will trend down from around
gale-force today, below that through the remainder of the period.
Gale-force winds will linger around the south side of the low
until it moves inland on Tuesday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The extended forecast covers late Tuesday through the weekend and
will have multiple weak features moving through the pattern. In
addition, the majority of the activity will stay south of the
southern mainland. However, the models generally struggle with the
handling of weak features further out in time and this forecast is
no exception leading to higher uncertainty with any new systems
moving into the area. The result was that ensembles were
preferred over the deterministic solutions increasingly toward the
weekend.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...SNOW ADVISORY 161
MARINE...Gale 119 120 130 131 132 138 139 170 173

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...DEK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MTL
LONG TERM...DWK