Small Craft Advisory 342, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
521 PM AKDT Wed May 1 2019

.ANALYSIS AND UPPER LEVELS...

The main upper level feature is a digging trough extending south
from a low center over the northern Bering Sea to over the north
pacific along 180w. This digging upper trough has set up broad
southwesterly flow across the North Pacific which is starting to
encroach on the AKPEN/Bristol Bay regions and western Gulf.
Satellite imagery shows abundant clouds and moisture streaming
north in conjunction with the upper-level flow. Observations and
radar data indicate rain over the AKPEN, Bristol Bay, and southern
Kodiak Island. The cirrus shield is also moving north across Cook
Inlet and the Kenai Peninsula.

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.MODEL DISCUSSION...
Models overall have a similar handling of the synoptic pattern.
Differences in sensible weather will be resolved by a combination
of the higher resolution models and hand edits.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist today. Rain
moves in Thursday and should drop the ceiling, and perhaps the
visibility, to MVFR. Gusty southeast winds are expected across
the airport complex late Thursday afternoon/early evening.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

An upper-level ridge will remain in place through this evening
bringing generally fair skies and light winds to the region.
Increasing cloud cover is expected after midnight as a weak cold
front begins to track into Southcentral. Rain will develop by
Friday morning under the front. Though some uncertainty still
exists, models are indicating a dry slot behind the front and
therefore the potential for a brief period of partial clearing
during the afternoon from the Kenai Peninsula northward through
Anchorage. A second round of widespread precipitation is then
likely Thursday evening, with the heaviest rainfall of around half
and inch expected over the Mat-Su Valleys (Palmer/Wasilla). Snow
is also possible in higher-elevated areas in the northern Susitna
Valley. Rain will taper to showers by Friday morning and cooler
higher temperatures will move into the region as well in the wake
of the front.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2...Thu and Fri)...
The broad upper level trough over the Bering will keep weather
unsettled across SW AK through the week. Within the trough itself
are two surface lows. One is located near Nunivak Island. The
other is located over the far Western Bering. A frontal boundary
is lingering over the eastern portion of the Bering. A shortwave
will move up along this boundary later tonight and merge with the
Nunivak Island low. This will allow the rain to increase across
the area into Thu morning as the front moves inland. While not
overly strong, the front will act as a cold front ushering a sharp
shift in wind direction and stronger southwest winds to mix down.
The bigger story with this system will be the colder air. Morning
lows Fri will be 5-10 degrees cooler than Thu morning. Most of
the precipitation will fall before the colder air arrives.
However, there still could be some limited accumulations for
higher elevations. Surface temperatures have been well above
freezing for sea level locations for several days, so this will
limit (negate) any accumulation.

Fri will remain breezy and showery as colder air and instability
pushes in behind the front. By late Fri night, a new ridge starts
to nudge into the area from the North Pacific. This could lead to
some widespread fog conditions across SW to start the day Sat.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2...Thu and
Fri)...
The Bering will remain relatively quiet with a few passing waves
of energy, but nothing overly strong or focused. Thu, a broad
trough with cold air aloft will linger over the area. This make
for partly cloudy conditions, light winds, and spotty showers. The
best chance for any steady precipitation will be right along the
SW Coast of AK as a frontal feature pushes inland.

Heading into Fri, an occluding warm front will slide into the
Western Aleutians. This will bring some southeasterly gale-force
winds as well as some steady rain to Shemya, Kiska, and eventually
Atka and Adak by midday. This front then slowly slides east as it
decays to start the weekend. The surface low itself will track
parallel to the Aleutian Chain, but remain south of the islands.

&&

.MARINE (Days 3 through 5)...
A low will move along the Aleutian Chain Friday through Sunday,
gradually weakening as it moves eastward. This will bring gale
force winds into the Central Aleutians by Saturday, but winds
will diminish through Sunday. In the Gulf of Alaska, the biggest
concern is on Friday, with winds just shy of gale force through
the Barren Islands and along the north Gulf Coast. By Saturday
these winds will have diminished and winds will remain sub-gale
force through early Sunday, with clearing skies overhead. Winds
across the northern Gulf will then be on the increase late
Sunday, with gales possible across the Barren Islands, as the
next front lifts north.

&&

.LONG TERM FORECAST (Days 3 through 7)...
On Saturday, showers will linger through the eastern half of the
state, while a more substantial low pressure system moves into the
Central Aleutians. Between the two systems, a weak ridge will
form, bringing a short-lived round of sunny skies to western
Alaska. However, as we move into early next week, the longwave
trough will begin to take over the weather pattern, and rainy,
unsettled weather will expand to include the east side of the
state as well. Expect the most steady precipitation to remain
along the coast, with showers moving further inland. By that time,
the low will have weakened enough that it won't be windy in most
areas, just cloudy and rainy across the bottom portion of the
state.
&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 181.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RMC
SOUTHCENTRAL ALASKA...AP/JA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MSO
MARINE/LONG TERM...LF