Small Craft Advisory 880, NWS Anchorage, AK

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

.ANALYSIS AND UPPER LEVELS...
A large low remains centered south of the Gulf near 51N 151W and
has filled slightly to around 957 mb. One frontal wave over
Southwest Alaska continues to lift northwest from the Bristol Bay
area over the Kuskokwim Valley this morning. In addition to
bringing gusty northerly winds, this system is also bringing a
wide variety of precipitation types with it as it crosses the area
early this morning. Further east, in the northern Gulf and
southern Southcentral Alaska, several other waves/troughs are
pushing through. One is evident in stronger radar echoes along the
southern Kenai Peninsula and over Cook Inlet. The next wave is
north of Middleton Island, and just starting to push into eastern
Prince William Sound with another large wave west of the Southeast
Alaska Panhandle. A front associated with a low near the Kamchatka
Peninsula is pushing into the Western/Central Aleutians.

&&

.MODEL DISCUSSION...
Synoptically models remain in fair agreement through the end of
the week. Smaller scale details such as the various waves rotating
through the northern Gulf remain more elusive. Of particular
concern are the details of a compact low tracking over Kenai
Peninsula Thursday afternoon. The GFS was the preferred model for
both domains.

&&

.AVIATION...
PANC...With the latest frontal system through and VFR conditions
expected to prevail through early afternoon...focus shifts to
next system coming through later this afternoon/evening. This
very compact low tracking over the Kenai Peninsula and not far to
the west of PANC will bring a burst of moderate to heavy rain
with MVFR to IFR conditions in the late afternoon or early evening
before pushing strong east to southeast winds out of Turnagain
Arm. Uncertainty in the precise track of the low leads to
uncertainty in the timing and strength of the winds (and whether
they will surface or be strong shear) but it is a system that
bears close watching.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A freezing rain advisory is in effect for the Copper River Basin.
Lingering warmer air aloft promotes rain freezing on surfaces
that have been in the upper teens to lower 20s overnight.

Light to moderate rain will fall over much of the area today
followed by a short burst of gusty winds. A stalled out frontal
boundary over the north Gulf coast spawns a new low pressure
system, as a shortwave trough rides the front from east to west.
This low brings a gale-force front into Prince William Sound this
morning. While a deformation band forms as the system backs into
the Chugach, spreading precipitation in the form of mostly rain
from the Matanuska Valley southward through the Kenai Peninsula.
There is a little concern that some areas will be below freezing
as rain begins, however, with such a deep above freezing
temperatures in place aloft, rain will bring temperatures up
above freezing pretty quickly.

This compact, yet dynamic system will bring some decent
precipitation rates in a short period of time. The upper
elevations of Anchorage/Eagle river could see snow mix down
briefly, roughly around 2000-3000 feet elevation. The better
chance for accumulating snow exists on the Kenai Peninsula, mainly
inland toward the Chugach where precipitation intensity will drag
cold air down toward the surface. Portions of the Sterling Highway
could see a quick accumulation of 1-3 inches of the heavy/wet
variety.

As the system passes into the Cook Inlet region, a tight pressure
gradient enhanced by pressure rises on the back side of the system
will bring winds up and over the Chugach with a few hours of
gusts into the 40s and 50s for upper elevations and 30s for lower
elevations, mainly in the Anchorage/Matanuska Valley areas.
Downslope warming will shoot temperatures up into the mid 40s for
these areas as well.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A weather front moving east to west across the area stalls over
the Kuskokwim Delta through early Friday, producing light
accumulating snow especially toward Bethel and possibly some areas
of blowing snow, but with only localized visibility reductions
expected.

A second front moves northwest along or just offshore by late
Friday bringing another round of light rain and snow, mainly
along the coast. However, there will also be the possibility of
overrunning light snow in the Lower Kuskokwim Valley Friday night
into early Saturday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A nearly stationary weather front resides along and near 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 Bering, and rain to the east. This keeps the
rain/snow probabilities on the high side through the next couple
of days across the Pribilofs. With the persistent northerly flow,
nearly continuous rain can be expected along the Bering side of
the Aleutians and Alaska Peninsula through the next few days,
occasionally mixing with or changing to snow as one heads east to
west across the island chain. Additionally, this front serves as
the primary focus for a thin line of northerly gale-force winds
through tonight, with the winds becoming stronger Friday into
Friday night along and west of the front over the Central Bering
as cold advection begins to increase, though the cold advection
will not be particularly strong. Toward the Western Aleutians, a
strong gale-force front will pivot across the region today into
tonight. High pressure will weaken this front and push it south of
the Aleutians by Friday. With the persistent northerly flow,
nearly continuous rain can be expected along the Bering side of
the Aleutians and Alaska Peninsula through the next few days,
occasionally mixing with or changing to snow as one heads east to
west across the island chain.

&&

.LONG TERM FORECAST (Days 3 through 7)...
An unsettled weather pattern continues across the Gulf and
surrounding coast through the long term as the next low pressure
pressure system moves in from the North Pacific early Saturday.
This storm system will bring the strongest winds, and heaviest
precipitation during the weekend into the early part of next week.
The southern mainland will see a few showers move inland with
temperatures remaining above season normals. To the west across
the Bering/Aleutians...a showery pattern with northerly flow on
the backside of the low pressure system ensues this weekend. The
next front moves into the west Bering on Monday before moving
swiftly northeast, with a stronger system following a similar
track on Wednesday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Freezing Rain Advisory...141.
MARINE...Storm Warning...119.
         Gale warning...125 129 170 172 177 178 179 180 181 185.

&&

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