Small Craft Advisory 324, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
416 PM AKDT Fri Apr 20 2018

.ANALYSIS AND UPPER LEVELS...
A long wave upper trough and a broad area of surface low pressure
with multiple low centers over southern Alaska are the main
weather features today. Low pressure across the Cook Inlet to MAT-
SU corridor and a weakening low over the northern Gulf are
producing widespread cloudiness and showers. Showers are mainly
rain, with a rain-snow mix at higher elevations and then mostly
snow over the northern Susitna Valley. A pinch in the pressure
gradient across Southcentral has given rise to brisk southerly
winds across the Copper River Basin and gusty gap induced flows
across Turnagain Arm. Out west, cloudy conditions area fairly
widespread. Rain and snow showers are evident over the Southwest
Mainland, mainly in the Bristol Bay zone. Generally mostly cloudy
conditions with rain showers prevail over the Bering Sea and
Aleutians. Gusty easterly winds, associated with a eastward
moving low and front south of the Aleutian Chain, were evident
across the central Aleutians.

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.MODEL DISCUSSION...
Short term model solutions through Sunday afternoon are reasonable
and in good synoptic agreement.

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.AVIATION...
PANC...VFR conditions will persist. Gusty southerly winds across
the airport complex will diminish during the early morning hours
Saturday, then increase again Saturday afternoon.

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.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A band of showers has formed over portions of the area this
afternoon. This band is forecast to persist until the loss of
solar heating results in its weakening. Scattered showers persist
over Anchorage and the Matanuska Valley, and are likely to
continue into the evening. Meanwhile, further north, the threat of
accumulating snow persists through Broad Pass. Once the sun goes
down that area should pick up several inches of additional
accumulation, as upsloping helps squeeze out additional moisture
from the atmosphere. During the day Saturday, the chance for a few
hit-and-miss showers returns to the Cook Inlet region as an upper
level wave of moisture locally enhances shower development. Those
showers too will be short-lived, and since it too will occur with
daytime heating, the precipitation should largely fall as plain
rain. Organized band development like what is occurring right now
is not expected again Saturday.

On Saturday afternoon, a low centered south of Sand Point will
swing a front into the southern Gulf, with precipitation breaking
out in Kodiak Saturday evening. The front will push northward
Saturday night, reaching the northern Gulf on Sunday. The front
and its associated cloud cover will reduce the atmospheric
instability, which should return the region to a more typical
precipitation pattern, with heavy precipitation occurring at the
coast, and downsloping keeping Anchorage and the western Kenai
Peninsula dry. The front will also invigorate a barrier jet along
the north Gulf Coast as it presses northward, resulting in gale
force winds all along the Gulf Coast for a time, with higher
gusts. The easterly flow will also enhance the Turnagain Arm and
Knik River Valley winds through Sunday. A triple-point low forms
over the southwestern Gulf Sunday evening resulting in more
precipitation on easterly flow through the overnight for Kodiak
and the north Gulf Coast.

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.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
An arctic trough is digging south over the region this afternoon
and is supporting the development of shower activity over the
Alaska Peninsula and north into inland Bristol Bay. This will
expand overnight into more organized rain/snow, especially over
the Lower Kuskokwim Delta where some minor snow accumulations will
occur. The parent upper low will retrograde into the Bering Sea
on Saturday with an increase in southeast flow aloft and a switch
to more sporadic rain showers.

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.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A low skirting the Western/Central Aleutians will move east then
north into eastern Bristol Bay Saturday night and Sunday. Broad
cyclonic flow and a mix of rain/snow showers will encompass the
eastern half of the Bering (including the Pribs) before a more
consolidated low center strengthens over the eastern Bering on
Sunday. An elongated gale force front will reach the western
Bering on Sunday and shift east into Monday.

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.LONG TERM FORECAST (Days 3 through 7)...
A progressive pattern will remain steadfast over the region
through the end of next week, yielding widespread precipitation
and gusty conditions across much of the Bering/Aleutians and
southern Mainland. Models are showing a series of lows and
associated fronts tracking through the Bering and north Pacific
throughout the period, with the fronts eventually pushing into
the Gulf region as the low centers approach the southwest coast.
The areas west of the Chugach and Alaska/Aleutian ranges are
still expected to see more of a downsloped-regime under
southeasterly winds, with some small breaks in the wind
periodically which will allow some precipitation to spill over.
However, by Thursday when the flow changes more to the SW over the
Cook Inlet region, we should see more precipitation making it
into the area. Along the Gulf coast, steadier precipitation is
expected with each frontal passage, along with gusty winds along
the northern Gulf and through favored channeled terrain.

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.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale Warning 119 120 130 131 138 178.

&&

SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHCENTRAL ALASKA...JW
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
LONG TERM...PEPE