Small Craft Advisory 611, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
432 PM AKDT WED AUG 3 2016

.ANALYSIS AND UPPER LEVELS...
The writing is on the wall with the pattern that is setting up.
There is abundant moisture moving up into the North Pacific.
Meanwhile, an Arctic trough is starting to slip south through the
Bering Strait. The trough has a 75 kt of the Polar Front Jet
supporting it at the 28,000' level. These two features will join
forces over the next 24 hours and start to establish the pattern
that will be with us for the next 7 to 10 days. But for today,
weak and brief shortwave ridging is making for mostly clear skies
across the southern mainland. All the fog from this morning in
Southcentral has burned off and some sea breezes are starting to
develop.

Over Southwest AK, the initial bands of precipitation
associated with the first front are already visible on the King
Salmon radar. Rain should start in earnest along the coast within
a few hours and then continue to march inland.

Over the Bering, the initial front has pushed through the Eastern
Aleutians and the Pribilof Islands creating gusty winds and
widespread rain. Over the rest of the Bering, weak ridging and
light flow is resulting in abundant low stratus and fog with some
light rain at times.

&&

.MODEL DISCUSSION...
Models are in fantastic agreement with the synoptic pattern. This
lends to high forecast confidence. There may be slight differences
in timing and amounts of precipitation, but the general idea of
wet southwest flow is very consistent among all the members.

&&

.AVIATION...00z TAF Anchorage...
Timing winds into Anchorage could be tricky late tonight into Thu.
As the front approaches from the southwest, we expect the SE
gradient to increase. At the same time, our down-Inlet gradient
will be increasing. So while the Turnagain Arms will blow, it will
be difficult to time exactly when and how strong they will get
into Anchorage International. It does look more like likely that
we will see a burst of winds Thu evening with frontal passage, but
overall southeast winds will pulse up and down.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Increasing clouds and chances of precipitation will spread over
Southcentral Alaska tonight, as broad southwesterly flow sets up
over the area and draws a weak low and associated weather front
northward. Rain over Kodiak Island will continue to spread
northward this evening and persist over much of Southcentral
through the end of the week, as a series of waves track over the
area in this moist southwest flow pattern. Ridging will build
across the North Gulf Coast in advance of the next wave tracking
in from the southwest on Thursday. This will lead to strengthening
pressure gradients along parts of the Northern Gulf Coast, and
give rise to brisk gap flows across Turnagain Arm/Portage Valley,
Knik River Valley, and Copper River on Thursday.

&&

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

The region will quickly turn to a wetter pattern as a broad area
of low pressure loft over the Bering Sea consolidates into a
larger and stronger low through the weekend. South to southwest
flow will mean all areas will see rain beginning this evening as
the first warm front moves in. Rain and cooler weather will
persist through Friday.

&&

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

A broad low will keep rain over the eastern half of the Bering Sea
and Aleutians through Friday. Another front will clip the far
western Aleutians near Shemya Thursday night and Friday bringing
steady rain. Otherwise, widespread sea stratus and fog will remain
dominant over the area as the area of low pressure remains
centered just east of the Pribilof Islands.

&&

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

For Day 3 (Fri night into Sat) southwest flow will continue across
Southcentral as a ridge of high pressure remains over the panhandle
and a low remains near Bristol Bay. This will send areas of
precipitation across mainland Ak. Over the Bering and Aleutians,
weak high pressure will be associated with areas of fog, and a
shortwave will bring rain to the western islands.

On Sunday the Bristol Bay low will be joined by the fast moving
short wave moving along the Aleutians. The associated fronts will
bring rain across the islands through Mon, and periods of rain
across the mainland through Tue. Conditions across the region will
improve by midweek, although moist and windy remnants of a
tropical system will begin to approach the western Bering on Thu.

The forecast utilized some Nam and GFS for day 3 and then
transitioned to WPC guidance that was heavily invested in EC and
EC ensemble solutions. The latter aided in the timing of the
numerous areas of precipitation moving across the region.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MO
SOUTHCENTRAL ALASKA...TP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
LONG TERM...DS