Small Craft Advisory 789, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
348 PM AKDT FRI OCT 7 2016

.ANALYSIS AND UPPER LEVELS...
A modified omega blocking pattern continues across Alaska and
surrounding waters. A sharp ridge extends from the southwest Gulf
of Alaska to over the mainland with a weakening upper low over the
eastern Gulf and a strong upper low over the central Aleutians. A
strong surface low was evident over Adak at noon today. The
central pressure was in the lower 950s. Winds associated with this
feature were gusting well into the 70s mph range over the central
Aleutians. Scatterometer (satellite derived winds) earlier this
morning showed a swath of 60 kt plus winds on the south quad of
the surface low. This verifies model forecasts of hurricane force
winds. The associated frontal system extends north into the
southern Bering Sea and east to the eastern Aleutians. Further
east a stationary baroclinic zone extends south from near the Gulf
of Anadyr across Bristol bay to south of the Ak Pen. Gales to
local storms force winds were evident along its boundary.
Precipitation overall is fairly light with this feature and
continues offshore of Southwest Alaska. Elsewhere a broad ridge
and weak offshore flow continue fair skies.

&&

.MODEL DISCUSSION...
Models overall are in fairly good agreement through the short
term (Sun) with the synoptic features. The most pronounced
differences over the last day or so have been the development of a
secondary low moving northeast toward the AK Pen on Sat. So
confidence is increasing on low position and track. However,
differences still exist of the intensity of the winds moving into
Bristol bay and inland areas of Southwest Alaska Sat afternoon
into Sun morning.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist through
Saturday afternoon.

&&.

SHORT TERM FORECAST SOUTHCENTRAL ALASKA...
High pressure will continue to dominate Southcentral Alaska
through the weekend and into early next week. This will keep most
areas with clear skies and light winds. The main exception is
Kodiak where a front will move in late Saturday bringing winds and
rain to the island.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The frontal system offshore remains stalled over Nunivak Island
and the Alaska Peninsula this afternoon with clouds and
precipitation only making it inland as far as the immediate
Kuskokwim Delta Coast and western capes. Winds along the coast
remain strong, while further inland dry sunny conditions prevail
under a strong upper level high over mainland Alaska.
Precipitation will gradually spread further east tonight and
Saturday as the frontal system associated with the deep Bering low
approaches the coast and shoves the large blocking mainland ridge
slightly east. A developing frontal wave lifting north over the
Alaska Peninsula Saturday evening will continue north across
Bristol Bay and up the west Coast Saturday Night. This frontal
wave will spread precipitation further inland and bring strong
east to southeast winds to Southwest Alaska...especially near gaps
and passes in in the Aleutian Range.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The powerful low is now north of the central Aleutians with the
stronger band of west to southwest winds associated with the
second wrap of the frontal system just about to lift north across
the central Aleutians this afternoon. The surface low looks to be
close to its deepest pressure central pressure and despite
beginning to gradually filling tonight and Saturday will carry a
swath of storm force winds north with it while Gales cover much of
the rest of the Bering. Southeasterly winds in the 40 to 45 knot
range with 50 kt patches will continue along the west coast in
association with the frontal system stalled there now and the next
system overrunning it.

&&

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

A high latitude omega blocking pattern will continue across the
Bering Sea and Alaska through midweek before the patten finally
breaks down. This will lead to continued sunshine and near normal
temperatures across the Alaska mainland but lead to a wet period
across the Bering Sea and Aleutian Islands. With the ridge portion
of the omega block over the mainland, an amplified trough and
upper level low over the Bering Sea and North Pacific will
continue to bring system after system through the Bering Sea. The
jet stream will become more zonal on Tuesday which will help bring
about the transition that will break down the upper level ridge
over the mainland. Models struggle quite a bit from Tuesday night
onward as the blocking pattern breaks down as the different models
bring about the demise of the upper level ridge over the mainland
in different ways and at different times. However, a potent area
of low pressure is likely to develop over the western Aleutians on
Monday and drift into the North Pacific south of the Alaska
Peninsula Tuesday night. Models have trended further south from
run-to-run as colder air coming off the coast of Russia will
prevent a lot of deamplification of the upper level trough over
the Bering Sea.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning 187.

MARINE...Storm Warning 173 174 175 176 180 185.
 Gale Warning 132 150 155 160 165 170 172 177 178 179 181.

&&

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