Small Craft Advisory 631, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
426 PM AKDT WED AUG 10 2016

.ANALYSIS AND UPPER LEVELS...
Water vapor satellite imagery this afternoon shows a large
disorganized longwave trough/upper low complex over Alaska. It is
a three-headed beast with separate upper centers over the Yukon,
the southwest Mainland, and another over the Alaska Peninsula.
The frontal zone associated with the system stretches from the
north gulf coast southwestward into the northern Pacific. While
there is a weak jet aloft over the Cook Inlet region, the main jet
energy is out west over the west/central Bering Sea.

Several disturbances in the flow are weakening overhead
Southcentral Alaska keeping light scattered showers going over
much of the area. The next area of interest is a broad band of
rain showers working in from Bristol Bay.

&&

.MODEL DISCUSSION...
Synoptically guidance is in great agreement with the upper level
pattern evolution. Given the complex interaction of the upper
level centers, waves breaking down within a positive tilt trough
and southwesterly flow, it's surprising we have as much agreement
as we do. Guidance does however differ on the former tropical
system moving into the central Bering Sea in frontal timing and
low track, but overall they look fairly similar. The GFS was the
model of choice initializing a bit better than the others.

&&

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

An active weather pattern continues through this upcoming weekend
as low pressure over the southwest mainland is replaced by the
next low which races in from the Aleutian Chain. The first strong
wave pushes a front along Kodiak into the Kenai and central Gulf
tonight, then spreads rain inland as it lifts slowly north on
Thursday. A secondary push with this system continues rain
development through Friday night. Showers will continues between
systems as upper low pressure remains aloft. Then next system will
be more organized and pushes a front into the western Gulf early
Saturday morning. This system will tighten the pressure gradient
along the northern Gulf bringing increased winds along the coast
and Turnagain Arm by mid day.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA...
The upper level low that has been over Southwest Alaska will stay
over the area tonight bringing more instability and showers. On
Thursday it will dissipate and showers will diminish moving into
Thursday night before the next system moves in from the west on
Friday. This new system will bring more rain to the area through
Saturday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS...
The remnants of Tropical Storm Omais are approaching the western
Bering with its front bringing rain to the Western and Central
Aleutians. After it moves into the western Bering Thursday
afternoon it will then weaken and track east across the Bering
making it to the eastern Bering Friday afternoon and the Alaska
Peninsula Saturday morning. Winds will be strongest around the low
with much of the Bering and Aleutians seeing gale force winds as
the low passes. Most of the rain associated with this system will
stay out over the Bering with the Aleutians seeing minimal
amounts. The exception is the weakening front over the Central
Aleutians tonight. Not until late Friday will areas of the Alaska
Peninsula see more than a light rain.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The Bering has a gale force low tracking the central/eastern
Bering by Friday. This system will track across near Port Moller
Saturday afternoon. The Bering will have a gale force northwesterly
winds as this system tracks across the gain. Therefore, look for a
showery weather regime for majority of the Bering/Aleutian chain
as we head into next week. By Sunday morning, this system moves
into the northern Gulf by Sunday morning. This synoptic feature
will remain in the northern Gulf, and gradually fills before
dissipating by Tuesday. The bulk of the precipitation with this
system will remain along the northern coastal communities. The
Anchorage Bowl will have drier conditions associated with
downsloping with predominantly southeasterly to easterly winds
along the Kenai/Chugach Mountains. The models were in fair
agreement with the GFS slowing the Bering low as it tracks from
west to east, and the Ecmwf was faster with this system.
Therefore, a blend of WPC, GEFS Mean, and the ECMWF Ensemble Mean
models were used through this weekend extending into the midweek.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...FLOOD ADVISORY ZONE 145 (YENTNA RIVER).
MARINE...GALES 175 177 178 185 411 412 413.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...ML
SOUTHCENTRAL ALASKA...KH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
LONG TERM...PD