Area Forecast Discussion
Issued by NWS Anchorage, AK

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204
FXAK68 PAFC 041256
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
356 AM AKST Wed Dec 4 2019

.ANALYSIS AND UPPER LEVELS...

Precipitation is continuing to taper off in Southcentral as a
weakening Gulf low exits to the east. Arctic air continues to
push into Southcentral from the north and west. The latest ASCAT
pass at 0900Z indicated low end gales out of Kamishak Bay and
over the Barren Islands. The surface pressure gradient between
the Gulf low and Arctic high pressure continues to diminish as the
low weakens and shifts eastward thus winds continue to trend
lighter.

Out west, a low centered roughly 70 miles south of Chignik is
generating some precipitation along the southern AKPEN. A low near
the Kamchatka Peninsula is steering a warm front northeastward
through the Bering Sea. Steady rain and south to southwest winds
over the western to central Aleutians persist behind the warm
front. The trailing cold front is in the western Bering,
currently approaching the western Aleutians. Over the Southwest
Mainland, temperatures are generally in the single digits to below
zero under clear skies and cold air advection.

&&

.MODEL DISCUSSION...

Models are in good agreement synoptically in the short term,
leading to generally good confidence in the forecast. However,
there are some key differences in the set up of several compact
lows that rotate around the Kamchatka low Thursday into Friday. In
addition, while there`s good agreement that a low will cross into
the eastern Bering from the North Pacific in the late Friday
timeframe, there`s uncertainty as to how close it will track to
the Kuskokwim Delta Coast. That said, there are some clear trends
in the overall pattern. In particular, expect another warm-up
across southern Alaska by the weekend.

&&

.AVIATION...
PANC...An MVFR deck has advected in from the north, but with
drying conditions aloft as surface high pressure builds over the
interior, expect this to scatter out later this morning. There`s
potential for fog tonight given stable conditions and ample
ambient moisture (snow)... but any lingering mid-level clouds may
limit fog development.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A low over the Gulf will slowly slide eastward today. Enough
moisture remains over the area to produce some light snow showers
and flurries this morning around Cook Inlet and the Kenai
Peninsula, as well as portions of the Copper River basin. A weak
trough will push eastward across the area tonight, with high
pressure building over Southcentral on Thursday. The trough will
pick up some moisture from the Gulf to give a chance of snow from
Prince William Sound eastward, including the Copper River basin.
Thursday night a weak front will move into the area from the
southwest, bringing increasing chances of snow again.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
High pressure over southwest Alaska has allowed temperatures to
drop below zero for areas around the Kuskokwim Delta and Lower
Kuskokwim Valley. However, a change is on the way with a front
approaching the area that is bringing a push of warmer air. Even
with the warm air, precipitation should still fall as snow for
most areas as temperatures will remain near or below freezing.
Strong winds will accompany the snow tonight for areas near the
coast creating blowing snow conditions. Winter Weather Advisories
have been issued for the blowing snow. Another front will
approach southwest Alaska Thursday night bringing more snow to the
area.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A front is moving through the western Aleutians that will make it
to the eastern Aleutians by this evening. It is bringing a strong
push of warm air with it and much of the precipitation will fall
as rain as it moves across the islands. A low will form along the
front in the North Pacific and help to reinforce the flow of warm
air and rain to the eastern Aleutians into Thursday. The front
will then track off to the north and east. Behind the front, cold
air will move back in bringing snow showers to the western
Aleutians.

&&

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

The focus continues to be on low pressure in the Bering Sea, since
the Gulf of Alaska remains quiet until Sunday when some small
craft advisory winds will be present. Low pressure in the Bering
is still expected to produce Gale Force winds. We can be confident
in this but that`s about it. Models are very inconsistent
starting Saturday, so placement and movement of low pressure is
still quite fuzzy. Particulars with low pressure in the Bering
will need to be handled the next couple of days. For now expect
gales, but be ready for timing and placement of them to adjust in
the coming days.

&&

.LONG TERM FORECAST (Days 3 through 7: Friday through Tuesday)...

The long term starts with cold air in place over much of our
forecast area. A longwave low pressure trough will also exist over
the Bering Sea. That begins to change Saturday with the
reamplification of a high pressure ridge to our east, forcing flow
out of the south from the bottom of the longwave trough out west.
This has the potential to change our weather back to about what it
was a couple weeks ago, with a warm air intrusion over southcentral
AK (warming temperatures) and melting snow. However, model guidance
uncertainty is quite high, with any consistency falling apart
Saturday. So, while ridge amplification changing our pattern looks
probable, the question remains where it will set up and how much
warming we will get. So, there is low confidence past Saturday and
it`s just too early to tell.

During the pattern change over southcentral, broad low pressure
will continue to hold in the Bering, which will bring multiple
rounds of inclement weather through the Bering and southwest AK.
This will be from smaller lows circulating within the longwave
trough. uncertainty is quite high in the Bering as well, so
particulars of individual low pressure systems will need to be
figured out when they enter the short term timeframe.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gales: 130 173 174 175 176 177 178 180 181 185 411 412
413
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...MM
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
MARINE/LONG TERM...BB



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