Small Craft Advisory 330, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
504 AM AKDT Sun Apr 22 2018

.ANALYSIS AND UPPER LEVELS...
An upper level low centered over the Bering just to the north of
the Pribilof Islands early this morning will rotate to the south
as a surface low south of the Alaska Peninsula and associated
upper trough lifts gradually north and east. An associated frontal
system stretching from the Alaska Peninsula east across the
central Gulf continues north, bringing Gales to the Gulf and
strong gap winds to the typical channeled locations such as
Turnagain Arm and the gaps and passes in the Alaska/Aleutian
Range. A deformation band extends from Bristol Bay north along the
Southwest Alaska coastal waters and then curves back to the
northwest towards the upper low near the Pribilofs. To the west a
frontal system associated with a deepening surface low tracking to
the east away from the Kamchatka Peninsula approaches the western
Aleutians.

&&

.MODEL DISCUSSION...
Models remain in good agreement through Monday with some small
differences becoming introduced Monday night and Tuesday
regarding the smaller scale troughs associate with the low in the
Bering and the triple point feature that rotates north across the
Bristol Bay coast.

&&

.AVIATION...
PANC...VFR conditions will continue. Northerly down-Inlet flow
will keep the easterly Turnagain Arm surface winds bent south and
away from the terminal. Wind shear however will still remain a
concern this morning. East to southeasterly flow across the area
will gradually diminishing tonight through Monday morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A strong front in the Gulf of Alaska is pushing toward the north
Gulf coast this morning bringing increasing winds and rain to
coastal regions. The wind through the typical gaps inland will be
a little different today as the low center near Kodiak will have
the Turnagain Arm winds turn down Cook Inlet today instead of
moving over Anchorage. The Copper River winds should also be
mitigated as the pressure gradient will be less in that region
today.
Tomorrow will see a little better chance for rain showers to make
it inland to the lee side of the mountains as the cross-barrier
flow will be less than today.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2...Sat and Sun)...
Just when signs of Spring were perhaps on the horizon, the
weather pattern is set to turn much more Fall-like over the next
several days. First things first, while the low SE of the Alaska
Peninsula is falling apart, it has helped to push some more
moisture up into Bristol Bay and through the West Coast. This
moisture is interacting with what is left of the lift associated
with the Arctic Trough over the Eastern Bering. This will allow
steady precipitation to redevelop across this area through the
day. By later today, this area of precipitation will push east and
spread inland from the coast through tonight. Ahead of this
front, gusty east to southeast winds will continue through the
day. These winds should also help keep the airmass warm enough
that the precipitation should remain all rain for population
centers as it does move in. However, by Mon, the front gets hung
up over the Lower Kuskokwim Valley. Cold air filters in behind it,
so those inland locations should see a gradual mix to some light
snow as precipitations winds down Mon afternoon. This forecast did
keep the PoPs higher over the Alaska Range, but we still don't
expect much accumulation at all.

By late Mon into Tue is when the bigger weather maker moves in.
A very broad (picture basically the entire Bering Sea) low
pressure center moves towards the Central Bering. As it does so,
plenty of jet support aloft and some upper level vorticity round
the base of the low. As they emerge on its SE flank (Bristol Bay),
the combine to produce another triple point low. This feature
looks to take aim right at the west coast as it tracks quickly
from north to south. This will bring moderate to heavy rain to
upslope areas and the coast. The bigger impacts though will likely
be strong east to southeast winds across much of SW AK. Gusts to
50 mph would not be out of the question, which is a little unusual
as we head towards the start of May. Then...as the parent low
moves towards the coast...a long fetch over the Bering with an
onshore pulse of winds could make for some high surf Tue-Wed. Stay
tuned to the forecast for updates regarding this potent weather
system.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The Bering is set to see a fairly active next couple of days. The
remnants of the Arctic trough will continue to impact the Eastern
Bering today with continued snow showers for the Pribilof Islands
through this morning. This feature will also keep rain falling
over much of the Alaska Peninsula until it is pushed east this
afternoon. Meanwhile, another stronger low is tracking towards the
Western Aleutians. Its accompanying gale-force front will slowly
weakens as it moves towards Adak and Atka today. On the south side
of the system though, cold air advection and a strong upper level
jet will keep gales in the forecast. The system then maintains its
strength in the upper 960mb-lower 970mb range as it continues to
recycle cold air across the entire Bering. Its progress slows and
nearly stalls over the Central Bering into Tue. This will leave
the whole domain vulnerable to showers (possibly mixing with snow
at times) and gale-force (or very near gale-force) winds. Mon
night into Tue, a low will develop near Bristol and strengthen as
it skirts through the Eastern Bering into the Bering Strait.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Beginning Monday night a broad area of low pressure will continue
to dominate the Bering with its front having pushed through the
southern mainland bringing rain to the north Gulf coast and
southwest Alaska. Current model runs are in better agreement than
previous runs with a triple point low forming in the eastern
Bering Monday night, but there does remain some discrepancies with
placement of this feature. These discrepancies grow through
Tuesday as the triple point low moves into the northern Bering
while the parent low tracks east. Impacts will remain fairly
similar for the southern mainland and Aleutians even through
guidance is struggling with where exactly to put these two lows.
On Wednesday high pressure will build in from the west and the
models fall apart with how to handle low pressure over the Bering
with widely varying solutions. This resulted in ensembles being
preferred for the remainder of the week into the weekend.
&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale 119 120 130 131 132 138 139 160 175-178 180-185.

&&

SYNOPSIS AND MODEL DISCUSSION...JR
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MSO
LONG TERM...DK