Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 180138
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
438 PM AKST Wed Jan 17 2018

.ANALYSIS AND UPPER LEVELS...
A vertically stacked low is slowly weakening as it spins over
Kodiak Island. Showers continue along much of the Gulf coast,
Kodiak Island, and Bristol Bay. Slightly cooler low level air
which came all the way around the south side of the low is now
beginning to wrap around the top of the low across Southcentral,
though precipitation-type remains rain for most of the region.
Some remaining warm aloft is also producing a mix of snow and
freezing rain from King Salmon northeastward to Iliamna, with
all snow south and west of Kind Salmon. Colder air is slowly
filtering in from the west which will change everything back
to snow. Cold air advection across the eastern Bering Sea and
Alaska Peninsula is leading to snow showers and gusty winds.

Out west, a gale force low is tracking northward just west of
the westernmost Aleutian Islands with an occluded front lifting
northward into the southern Bering Sea. Building heights out
ahead of this storm system are the beginning of what will
develop into a strong blocking ridge over the Bering Sea later
this week. This will lead to a major shift in pattern, with
Arctic air pouring southward across the eastern Bering Sea
and much of mainland Alaska.

&&

.MODEL DISCUSSION...
Models are in very good agreement with large scale features and
forecast confidence remains above average. The primary challenge
will be dealing with the remnants of the low over Kodiak and
precipitation over Southwest Alaska, with abundant low level
moisture favorable for low ceilings and fog.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. The LLWS that
had been in the forecast for this afternoon was removed as
Turnagain winds developed weaker than initially expected with no
sheer layer on recent ACARS soundings.

&&

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

A transitional pattern begins tonight as the Gulf low weakens
into an open wave with the remnant trough stretching across the
southern mainland between two building ridges. Winds are expected
to be relatively light across the southern mainland through Friday
as the Bering ridge slowly evolves into the dominant synoptic
influence. The trough over the southern mainland helps to pull the
colder Arctic air toward Southcentral and the gulf through the
end of the work week. A few breaks in the clouds are expected,
however the weak low continuously streams clouds overhead which
also prevents large temperature drops.

Over the Gulf, southeasterly flow changes to north and west
tonight and remains to be low impact as the trough moves to the
eastern Kenai through Thursday night and meanders in the vicinity
through Friday. The next North Pacific low tracks south of the
Alaska Peninsula early Friday, continuing on a due east path
through the day. Flow across the gulf will be light and variable
during this time as the low is relatively weak.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA...

A low near Kodiak is continuing to support sufficient upper level
deformation for widespread snow (with a little rain at times)
across Southwest Alaska with the exception of the Kuskokwim Delta
Coast. The heaviest snow band stretches from the Alaska Peninsula
to the Nushagak Hills. This will continue through the overnight
before deformation weakens Thursday and snow becomes relegated to
the Alaska Peninsula. Thereafter, cold offshore flow increases
dramatically with the net result being colder and drier weather
Thursday night into the weekend.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS...

A gale force low over the western Bering will continue to weaken
with the associated front stalling southwest of the Pribilof
Islands. Another low over Kodiak Island will continue to support
broad northwest flow over the eastern half of the Bering Sea
through Thursday before weakening. Thereafter, ridging will build
over the Bering Sea allowing for the flow to switch to a more
easterly direction over most of the Bering Sea.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The long term forecast is still on track today with models in good
agreement showing a major pattern shift beginning this weekend. A
high amplitude blocking ridge will develop over the western Bering
which will cause a longwave trough to descend south across the
state by Sunday. The trough will drag brutally cold, eye lash
freezing air down from Siberia, where temperatures were recorded
as low as -80F earlier this week. This will lead to a significant
cold air outbreak over most of interior and western portions of
the state next week. Temperatures across interior sections could
drop into the -30s and -40s by Monday with locations along the
Bristol Bay coast dropping into the negative single digits or even
negative teens. Though this is not shaping up to be a record
breaking event, temperatures will be noticeably colder than it
has been all winter, especially when factoring in the expected brisk
northerly winds, which could drop wind chills as low as -50
across interior portions of SW Alaska.

Southcentral looks to escape the brunt of the cold air as the
Alaska Range will block the cold core to the north and west sides
of the range. In fact, a weak surface low looks to develop in the
Gulf by Tuesday which could bring periods of light/dry snow to
the mountains and communities along the Prince William Sound from
Tuesday through the end of the week, which should also pump in a
little bit warmer air from the south helping to moderate
temperatures across Southcentral a bit. An upper level low looks
to drop out of the Arctic around mid week bringing another
reinforcing shot of cold air to the state. The low center should
track south across the western half of the state, which would
again concentrate the coldest air to SW Alaska. If the low tracks
more to the east, as shown in previous GFS runs, cold arctic air
could make its way into Southcentral, though models seem to be
agreeing more on the western track of the low.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale 178
         Heavy Freezing Spray 180 181
&&

$$

SYNOPSIS AND MODEL DISCUSSION...SEB
SOUTHCENTRAL ALASKA...KH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
LONG TERM...KVP



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