Small Craft Advisory 881, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
430 PM AKST Thu Nov 10 2016

.ANALYSIS AND UPPER LEVELS...

A longwave trough stretches from the Gulf of Alaska into the
eastern Bering with a consolidated upper level low centered in
the the southern Gulf of Alaska. To the north, a potent upper
level shortwave is over the Kenai Peninsula, with an associated
tight surface low. This low has been supporting a low level jet
along the north Gulf Coast with storm force gusts, and is
supporting gap winds through Seward and Whittier. In addition,
this low has been bringing a mixed bag of widespread precipitation
across much of Southcentral. In the western portions of the Copper
River Basin, where deeper and colder air is well-entrenched,
precipitation has been falling mainly as snow. However, in the
eastern and central Copper River basin, some freezing rain has
been occurring near and south of Glennallen, as warmer air
associated with the low pushes northward. Meanwhile, broad
northerly flow is established across the Eastern Bering and
bringing widespread showers.
&&

.MODEL DISCUSSION...

Models are in generally good agreement today in the short-term,
although the higher resolution NAM is capturing the low level jet
currently along the North Gulf coast the most accurately. Models
continue to show fairly good agreement as the weather pattern
remains active into the midterm.

.AVIATION...
PANC...With the strong low passing just a little south of the
airport this afternoon and continuing to move northwest the winds
will switch to the southeast and become gusty early this evening.
This will also likely usher in some turbulence around the area as
well. Precipitation type will remain all rain. Conditions should
improve by midnight as the low weakens and moves farther from the
area.

&&

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

The small but strong low moving across the Kenai Peninsula this
afternoon is bringing significant winds to coastal locations.
These winds are expected to diminish rapidly this evening as the
low moves inland and weakens. This low is also associated with
much warmer air streaming in from the Gulf, which by early evening
will end any lingering threat of freezing rain. This will also
raise snow levels above the level of valley floors throughout the
region.

On Fri the parent low will move to the north Gulf coast in the
afternoon and then inland near Prince William Sound. Another
round of wind (not as strong as this afternoon's wind) with
coastal rain, and snow in the mountains is expected. Behind the
low, warm and moist southeast flow will continue to spread rain to
the coast on Sat. Inland areas on the downslope side of the
Chugach and Kenai mountains will be dry.

 &&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A weather front stalled over the Kuskokwim Delta continues to
produce light accumulating snow and gusty winds over the area
through Friday morning, with some localized areas of blowing snow
reducing visibilities. A second front associated with a low
developing over the eastern Bering Friday will bring another wave
of rain and snow mainly along the coast, with the possibility of
overrunning light snow in the Lower Kuskokwim Valley Friday night
into early Saturday. A more organized front, associated with a
low south of the Alaska Peninsula, will track northward into the
Southwest Mainland Saturday morning brining gusty winds and more
precipitation the area through Sunday morning.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A nearly stationary weather front will remain along the 170th
longitude line for much of the next couple of days, and will
largely serve as the dividing line between snow to the west over
the Central Aleutians/Bering, and rain to the east. Predominant
northerly flow over the central and eastern Aleutians/Bering will
continue to filter in gusty winds and cold arctic air over the
area through Sunday morning. With cold and gusty northerly flow
and persistent snow showers over the central and eastern bering,
there remains some potential for blowing snow to cause some minor
reductions to visibility over the Pribilof islands tonight into
Friday morning, and again overnight Friday into Saturday.

Toward the Western Aleutians, a strong gale-force front will
pivot across the region tonight. High pressure will weaken this
front and push it south of the Aleutians by Friday morning,
bringing colder northerly flow over the area along with the
potential for some snow showers.

&&

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

An upper level low will remain situated across the Alaska
Peninsula through Monday morning as another upper level low over
eastern Russia forms a pseudo-Rex block feature. This blocking
feature will break down Monday afternoon as the upper level
pattern amplifies in response to a potent jet streak and upper
level disturbance pushing off the Kamchatka Peninsula. In the mean
time, the upper level low over the Alaska Peninsula will have a
front that extends into the North Pacific. A triple point low
looks to develop along the front and move into the southern Gulf
of Alaska on Monday. This will bring another potent area of low
pressure toward the northern gulf coast with another gale force
barrier jet (possibly stronger deepening on how quickly the low
wraps up) and another decent rainfall event to much of the Gulf
coast and eastern Kenai Peninsula. Downsloping during the event
looks to keep much of the interior portion on the dry side as well
as keep temperatures above normal. However, a transition from
above normal to near normal (possibly below normal across the
Copper River Basin) will return as the upper level pattern shifts
and colder air finally filters in over the mainland.

The Bering Sea will be quiet for much of the extended period as
the bulk of the action will be east of the Alaska Range. Gale
force winds will be seen across the Pribilof Islands south toward
Dutch Harbor due to the tight pressure gradient but lighter winds
are expected for the western half of the Bering. This all changes
on Wednesday as a strong low will push off Kamchatka and into the
Bering Sea but models struggle on the exact placement and timing
of this low.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Freezing Rain Advisory 141.
MARINE...Gale 119-125 129 170 172-179 181 185.

&&

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