Small Craft Advisory 300, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
434 AM AKDT Sun Apr 9 2017

.ANALYSIS AND UPPER LEVELS...

Southern Alaska remains in a rather weak flow regime aloft as the
main Pacific jet stream remains well south of the forecast area.
In terms of features, there is an occluded gale force low across
the Western Bering Sea/Aleutians with a high latitude blocking
high over the Beaufort Sea. There is an upper trough over Western
Alaska which is forming due to the merger of two separate PV
anomalies. There is another shortwave trough over the Eastern Gulf
of Alaska which is lifting north toward the coast, and this
feature will move inland today. Isolated to scattered rain showers
are largely relegated to coastal regions near the Alaska
Peninsula and the Kenai coastline/Kodiak Island although some
isolated activity is trying to form in the lee of the Chugach (in
easterly flow) Mountains this morning. Weak low pressure over the
west coast and broad southerly flow aloft is keeping the pressure
gradient directed onshore, albeit weak.

&&

.MODEL DISCUSSION...

The models are in excellent agreement with the general broad
pattern through next week after being in relatively poor agreement
a couple days ago. However, the smaller details are not as well
handled, especially in the next 36-48 hours as two shortwaves
move northwest toward the Gulf Coast. All the models show similar
depictions as a whole, but with different timing and strength. As
a whole, the general idea is showers and clouds will increase
with each trough passage, but small scale details and the
addition of some afternoon convective forcing keep certainty on
the lower end. However, sensible weather differences will be
less significant, so forecast confidence is generally high as
spring like weather will continue as we head into the next week.
Model preference was toward the GFS on both domains.

&&

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

The airmass over Southcentral Alaska is relatively unstable with
cold air aloft and surface temperatures warming up nicely during
the day. A number of weak short waves are embedded in the
southeast flow aloft which are bringing some rain and snow showers
to the area today. The forecast challenge is to try and time the
short waves as models differ in their location and timing from run
to run. The result will be a chance of some showers...especially
in the afternoon over the inland areas of Southcentral with
showers likely over the north Gulf Coast...including Kodiak
Island.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
Southeasterly flow returns by this afternoon as low pressure
approaches from the west while weak ridging builds across the
central interior. Isolated to scattered showers still continues
to develop today across the southwest as upper level short waves
rotate through the upper flow. A drier pattern settles in for
Monday and Tuesday as surface ridging builds from the interior,
while at the same time, an upper level ridge amplifies and moves
inland from the Bering.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...

A surface low and associated front tracks along the western chain
today and then slips south to the Pacific tonight. This weakening
system will bring gusty small craft winds and mixed precipitation.
A stronger system pushes a front into the western chain by early
Monday and takes a slow northerly track progressing into the Bering
on Tuesday. This occluding system bottoms out around 970 mb just
south of the western Aleutians Monday night. Max easterly gales
can be expected along the frontal boundary as it pushes through
with precipitation falling as rain due to the warm subtropical
nature of this system.

&&

.LONG TERM FORECAST (Days 3 through 7)...

The long term forecast will not be seeing drastic change from the
current forecast solution. The week begins with high pressure over
the eastern mainland effectively blocking the the approaching low
in the Gulf of Alaska and results in the Bering Sea low also just
having a glancing blow at southwest Alaska then moving southeast
to the low complex south of the Gulf of Alaska. The Bering Sea and
Aleutians will remain very active as yet another strong storm
moves in on the heels of the exiting storm and rapidly sweeps
across the Aleutians to the Bering Sea coast by mid week. This low
will then be followed by yet another strong low that will take a
more northern track across the Bering Sea.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale 175-178.

&&

SYNOPSIS AND MODEL DISCUSSION...JRA
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KH
LONG TERM...SS