Small Craft Advisory 782, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
446 AM AKDT Mon Oct 16 2017

.ANALYSIS AND UPPER LEVELS...
The remnants of an upper low is over the Kenai Peninsula with a
weak ridge over southwest Alaska. There are some lingering showers
over Prince William Sound and the Gulf Of Alaska. The circulation
of the vortex is discernible from the Middleton Island radar this
morning. There is an upper level low over the northwest Bering
Sea. The jet stream over the northern Pacific continues to barrel
across the region. There is a weak shortwave over the
central/western Aleutians moving rapidly eastward.

&&

.MODEL DISCUSSION...
For the first 24 hr period, the mass fields amongst the
NAM/GFS/ECMWF/GEM are similar. As time elapses, the model
consensus quickly erodes. Compounding the magnitude of the
uncertainty is the fact that the run to run continuity with both
the GFS and the NAM has been below average. The focal point for
this morass is the low that moves over the Aleutians on Tuesday.
The ECMWF brings the track of the low more to the south, while the
Canadian GEM and the GFS are both pinging into a more northerly
track. Additionally, the pace of the storms motion and the
possible development of a triple point low are at stake. While
there is high confidence of another low impacting the North
Pacific and Gulf of Alaska early this week, there is still some
degree of uncertainty about the evolution and the morphology of
the low itself.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist.

&&

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

Partly cloudy to mostly clear skies and cold northerly flow
continue across the mainland will continue through the middle of
the week. A weak vertically stacked low near Middleton Island is
spreading bands of clouds across most of Southcentral Alaska, but
shower activity is confined largely to the north Gulf coast. This
low will drift eastward through tonight, allowing cloudiness to
gradually diminish across most of the forecast area. Gusty
offshore winds will continue around Prince William Sound, with
lighter winds and colder temperatures inland. With clearing skies,
each night is still expected to be a few degrees cooler than the
previous, as a cooler airmass continues to move into the area from
the north. There has been a bit of a shift in the models in
regards to a low moving into the southern Gulf on Tuesday
afternoon. The general trend has been for a slightly stronger and
more northerly track. Thus the morning forecast reflects a bit
more in the way of wind and weather from Kodiak through the
offshore zones. Nevertheless, even with this new trend, the only
impact for the southern mainland will probably be a renewed push
of offshore (northerly) winds by midweek, with plenty of sunshine
to go around.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...

Isolated to scattered rain showers will continue along the
western coast of Alaska through this evening as an area of low
pressure over the Gulf of Anadyr continues to pump moisture
toward Southwest Alaska. As the low pressure system continues to
dissipate this evening, the influx of moisture will likely come to
an end and colder air out of the arctic will descend across
Southwest Alaska. The jet stream will remain well south of
Southwest Alaska which will keep any low pressure systems systems
that develop over the northern Pacific Ocean will quickly be
shunted into the Gulf of Alaska and away from region. Temperatures
will gradually cool off several degrees over the next several
days to more seasonable temperatures.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...

An active pattern will be observed along the Aleutian Islands and
southern Bering Sea over the next several days as the jet stream
over the northern Pacific Ocean will spin up multiple low pressure
systems. The first system is an area of low pressure currently
located near Shemya. Based on Satellite imagery, the low is in the
process of intensifying and will track just north of the western
and central Aleutians throughout the day. By tonight, a potent
triple point low looks to spin up not too far from Dutch Harbor
but models are struggling very much with this feature. It's tough
to tell how much impact on winds this feature will have but based
on the jet stream, it looks like the triple point low will
quickly become the dominant low with the low currently near Shemya
fizzling out. Storm force winds and possibly a lightning strike
or two will be possible this afternoon on the back side of the
low. This complex system will quickly move into the Gulf of Alaska
late Tuesday night with multiple low centers as triple point lows
continue to form along the frontal boundary. A separate frontal
boundary will enter the western Bering Sea Wednesday afternoon but
this one should be much weaker than the system currently pushing
through the western Bering Sea.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The mid to long term forecast beginning Tuesday night shows an
active storm track that will primarily stay south of the southern
mainland. This will bring more rain and winds to the Aleutians
through much of the week. There remains disagreement for the
exact track and timing of the low that moves through late in the
week but all guidance keeps it south of the southern mainland
until the weekend. That would leave mainly dry and cold for the
southern mainland until Saturday where there becomes a fair amount
of uncertainty as to what the low will do as it moves toward the
Gulf.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...GALE 174 175 178 413. STORM 176 and 177.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...AD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MC
LONG TERM...DWK