Small Craft Advisory 632, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
511 AM AKDT THU AUG 11 2016

.ANALYSIS AND UPPER LEVELS...

Water vapor satellite continues to depict a nearly stationary
upper low over the middle and upper Kuskokwim River Valley this
morning. A fairly sharp shortwave is currently rounding the base
of the trough extending south through Bristol Bay and well into
the Pacific. Strong southwest flow aloft ahead of this feature is
pushing a widespread area of rain through much of southern Alaska
ahead of the base of the trough. Weather radar depicts the entire
Cook Inlet region with light rain falling, though weak downsloping
over the Matanuska Valley is currently inhibiting the rain from
reaching the ground toward the Palmer area.

Out west, a flattening ridge dominates the Bering region. However,
a gale-force low (the remnants of a former typhoon) are moving
east into the southwestern Bering. A northwest-southeast oriented weather
front precedes the low and is moving toward the Pribilofs and
Eastern Aleutians.

&&

.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 eastern Bering region in frontal timing
and low track, but overall they look fairly similar.

&&

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

An upper level low centered near the Kuskokwim Delta will bring
unsettled weather to much of Southcentral today, as the vort max
progresses towards Kodiak Island this evening and the Kenai
Peninsula Friday morning. Broad southwesterly flow will transport
moisture towards Soutcentral most of the day as the vort max
approaches. Meanwhile onshore flow will support heavier
precipitation along the northern Gulf Coast including Prince
William Sound and the Eastern Kenai Peninsula. There is currently
some uncertainty in the timing and location of most intense
precipitation, but the GFS has shown the most consistency.
Over the short term, rainfall will be heaviest on Friday, as the
vort max moves from Kodiak to the Kenai Peninsula. A second
upper level low follows quickly on its heels and moves from
bristol bay towards kodiak island saturday afternoon. &&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The low that has dominated the Southwest mainland for the past few
days will begin to dissipate this morning, which will result in
showers beginning to taper off by later tonight. This will be a
short lived break from the showery weather, as another system
will approach the Southwest coast by Friday afternoon and bring
rainy weather back to the area through Saturday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The remnants of Tropical Storm Omais has started to push into the
Western Bering this morning, with its associated front bringing
rain to the Central and Eastern Aleutians today. This system will
slowly weaken as it tracks eastward across the Bering through
Friday, and eventually end up over the Alaska Peninsula by
Saturday morning. The strongest winds will be located on the
southern periphery of the system, 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 in comparison. Not until
late Friday will areas of the Alaska Peninsula see more than a
light rain as the low center tracks over the area.

&&

.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...NONE.
MARINE...Gales...170 172 173 174 175 176 177 178 185
FIRE WEATHER...NONE.

&&

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