Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 080203
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
503 PM AKST Sun Mar 7 2021

.ANALYSIS AND UPPER LEVELS...

In the upper levels, the broad low pressure system over the
Kamchatka Peninsula has moved over the western Bering with the
associated trough now extending south across the western Aleutians.
Farther east, the ridge over western Alaska is continuing to move
east. Between the two upper level features, deep southwest flow
is bringing relative warm air and areas of precipitation to the
western and central Aleutians and western Alaska. A potent low
pressure system continues to rotate over the eastern Gulf.

Additionally, low level ash emissions from the Veniaminof Volcano
located north of Perryville remained visible on satellite imagery.
Flow was westerly through the last few hours but has begun to turn
southerly.

&&

.MODEL DISCUSSION...

Model guidance is in general agreement with the synoptic features
through mid week, although there are slight differences with
timing, as well as the strength of the low level system
developing in the western Gulf, moving toward the Prince William
Sound area for Wednesday. At this point, the differences don`t
make a big difference on the forecast, but will likely make an
impact as we move closer Tuesday. By the end of the week, models
develop more significant differences with regard to the systems
possibly affecting the Bering and western Aleutians.

&&

.AVIATION...
PANC...VFR conditions will prevail through the rest of the
daylight hours. Expect MVFR vis/cigs to develop with fog potential
overnight, with IFR cigs possible. Light northerly winds will
continue.

&&

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

Dry weather tonight and Monday across Southcentral. A tight
pressure gradient has set up over Southcentral. Enhanced gap winds
and offshore winds will continue this evening and will be most
pronounced over the Barren Islands and Copper River Delta. Early
Monday morning an upper level ridge will into the region,
ushering in warmer air aloft. Warm air over cold air is inherently
stable. It`s possible that fog may develop in portions of
Southcentral Monday morning around Cook Inlet, the Mat-Su Valleys
and Copper River Basin. Looking upstream, there is a front moving
into Western Alaska. By late Monday, Katmai National Park and
Kodiak will get precipitation from the leading edge of the
precipitation shield. Tuesday morning, moisture will have
advected into Seldovia, Homer and up the Cook Inlet. By Tuesday
afternoon, the next batch of snow will be impacting the Anchorage
Bowl, Talkeetna, Hatcher Pass and the Parks Highway. Tuesday and
Wednesday Prince William Sound and the Chugach Mountains will see
the heftiest accumulations of new snow.

&&

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

A complicated forecast is in store for Southwest AK. A very strong
front is slowing encroaching from the Bering. A persistent push
of warm air ahead of the front keeps Southwest mostly above freezing
today and tomorrow. Precipitation is expected to be a rain/snow
mix for most inland areas or all rain along the coast, AKPEN and
eastern portion of the Kuskokwim Delta from Bethel east. Gusty
winds ahead of the front, with the strongest winds along the
coasts, should keep temperatures on the warmer side. Thus,
blowing snow is not expected to be an issue with this system.
Rain/snow mix will track across the Southwest Mainland from west
to east with the front. Colder air returns behind the front,
dropping temperatures back to below freezing for most areas by
Tuesday. Several embedded weak meso-low within a series of
shortwaves behind the low track across the Bering and Southwest.
Overall, Southwest should become relatively quiet by Tuesday
morning. Any lingering precipitation behind the front, or any
precipitation associated with these mesolow, will be brief periods
of light snowfall.

&&

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

A front continues on track towards the Southwest Coast this
afternoon, with strong southerly flow ahead and along the front.
The warm air push across the eastern Bering allows for the rain
showers to continue across the Eastern Aleutians, Southern AKPEN
and Pribilof Islands through tonight. Behind the front, winds
begin to diminish and become primarily westerly, carrying much
colder air with it. Freezing and heavy freezing spray will be
reintroduced into the norther and western portions of the Bering,
as well as along the Western Aleutian coasts, by tonight.
Multiple shortwaves and embedded meso-low push across the Bering
behind the front as well. Periods of light snowfall is likely
along the Western and Central Aleutians as these waves pass. Broad
high pressure moves across the Bering on Wednesday.

&&

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

Bering: A series of troughs with locally up to small craft winds
will cross the Bering from west to east on Wed, with small craft
or lower westerlies expected away from the troughs. Westerly winds
could locally be as high as gales on the south side of each
trough, but confidence for the track and timing of each wave is
low at this time. Seas on Wed up to 10 feet. Another front will
approach the western Bering by Thu, with southerly gales spreading
into the western Bering Thu morning into early Fri. Seas building
to up to 20 ft across the western Bering by Thu and Fri. A North
Pacific low may approach the southern Bering and Central Aleutians
on Fri, but track and timing for this next low remains uncertain.
Expect potential for winds to increase to high gales to possibly
low storms over parts of the central to western Bering for Fri,
however exact timing and track of enhanced winds will depend on
the low track.

Gulf of Alaska: A low will move into the central Gulf and then
into or just south of the Prince William Sound on Wednesday.
Widespread westerly small craft to gale force winds will spread
across the central and southern Gulf south of the low center
through Thu. Seas building from 10 to 15 feet from Wed to Thu. The
low center will dive south towards the southern Gulf on Fri with
small craft to gale force winds continuing and becoming
northwesterly over the western gulf through Fri. Seas building to
20 feet in the western Gulf on Fri.

&&

.LONG TERM FORECAST (Days 4 through 7: Thursday through
Sunday)...

The large scale pattern from long term guidance remains in decent
agreement for the Bering, Gulf and mainland AK, but some
discrepancies do emerge across mainly the Bering by Saturday.

A longwave trough is likely to become the dominant influence over
the mainland by Thursday and Friday this week, and the preceding
warm spell over Southcentral early in the week will likely be cut
short as a cold, Arctic air mass spills in from the northwest.
This pattern will favor much colder and drier than average
conditions over mainland AK from Wednesday to Friday, with
offshore flow and the potential for stronger outflow winds for the
typical spots near the North Gulf Coast from Thursday to
Saturday. Longwave ridging will develop into the eastern Bering,
while low pressure and troughing will persist in the northern and
western Bering. Models diverge with the handling of a stronger
shortwave rounding the base of this trough, with varying degrees
of northeast progression of the wave depicted by operational
models on Friday and Saturday. Despite the uncertainty, this will
generally favor active and stormy conditions over the western
Bering with multiple rounds of rain/snow and stronger southerly
winds.

By Sunday, model agreement continues to lessen with global models
trying to progress the western trough towards the Southwest/AKPEN
while the longwave ridge moves farther east into the mainland
with the Arctic air beginning to retreat up into the Yukon. This
could lead to a warming trend beginning over mainland AK with the
potential for another frontal system to move up the AKPEN into
southcentral. However, the progress of this next system and
related warming will greatly depend on how quickly the upstream
ridging and surface high pressure associated with the cold air
mass erode or advect east. This is a dynamic models can be overly
optimistic about, especially looking this far out in time, so the
cold and dry pattern for Southcentral could still linger on for
longer into next week.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Heavy Freezing Spray Warning 185 411.
     Gale Warnings 155 160 165 170 172 179 180-185 414.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...NR
SOUTHCENTRAL ALASKA...PS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KM
MARINE/LONG TERM...AS


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