Small Craft Advisory 602, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
448 PM AKDT Mon Aug 14 2017

.ANALYSIS AND UPPER LEVELS...
The low pressure system that affected much of the mainland over
the weekend has mostly moved off to the northeast, with upper
level troughing still extending over the southern third of the
mainland this morning. Satellite indicates moisture lingering in
the base of the trough along an east-west orientation from the
eastern Copper River Basin through the northern Kuskokwim Delta.
Although showers have ceased for the most part around the region,
mid to upper level clouds are keeping Southcentral from drying out
too much from this weekend's rain.

In the southwest, onshore flow and lingering moisture brought fog
to the Kuskokwim Delta this morning, with some low clouds through
Bristol Bay and up into the Alaska Range. Out in the Bering Sea,
colder air and northwesterly drying flow behind the upper level
trough is bringing some instability, so the Pribilofs and Central
Bering are seeing some blue skies today.
&&

.MODEL DISCUSSION...
Models are in good agreement and have had good run to run
consistency for the past several days. The timing on the next rain
event for Tues/Weds has slowed slightly from previous runs, but
overall is in line with the forecast from last week. For the
short term, a NAM/GFS blend was chosen to pick up on terrain
details.

&&

.AVIATION...
PANC...VFR conditions will persist. A Turnagain arm wind is
expected to pick up late this afternoon, but should end before
midnight as the pressure gradient decreases. No other aviation
impacts are expected.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Southcentral will continue to see a break in precipitation
through the day tomorrow as weak ridging builds over the area in
between two lows to the east and west. Skies should remain partly
cloudy and mostly dry tomorrow though a few isolated rain showers
may form over the Kenai and Chugach Mountains as well as Prince
William Sound in the afternoon. A low dropping southeast out of
the Bering Sea on Tuesday will be the next weather maker for the
region. As the low center moves over the Aleutian chain on Tuesday
night a predominately southwest flow will develop over
southcentral leading to increased cloud cover and a push of
moisture into the region. Rain is expected to develop by Wednesday
morning as a shortwave trough moves over the area, with heaviest
amounts expected along the Gulf Coast into the Prince William
Sound. Rainfall totals will be less than what was observed over
the weekend, but should vary between 0.25 - 0.5 inches for inland
areas to 1-2 inches along the coast through the end of the day on
Wednesday.

&&

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

Cloudy and unstable conditions will continue across the Southwest
mainland for the short term. Currently a fairly weak upper low is
supporting light showers across the Kuskokwim Delta and Bristol
Bay Regions. More widespread and intense rainfall is anticipated
Wednesday as the upper low near the Pribilofs pushes eastward
across the Alaska Peninsula, and a separate upper level low dives
southward towards the Kuskokwim Delta. This PV anomaly will
intensity as it stretches across the Kuskokwim Delta to the
Alaska Peninsula and pushes eastward.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

Throughout the short term, surface high pressure will maintain
hold over the southern and western Bering, while a trough will
remain over the eastern Bering and over Bristol Bay. A low level
jet will develop between these two features and support near gale
force winds and cold air advection. This will keep the lower
boundary layer well mixed and prevent fog from being too widespread
or dense.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The models are still struggling with the timing as the closed
upper level low over the Chukchi Sea as it drops southward into
the Southwest Alaska region by Thursday morning. While the
associated longwave trough continues to move eastward through the
Southwest Alaska area into the Gulf of Alaska by Wednesday evening.
The GFS model is the outlier with these synoptic features, and
very progressive with its speed of this system as it tracks eastward.
By Thursday evening the aforementioned closed upper level low is
located over the western Gulf before moving to the lower
Southeast Panhandle by Friday afternoon. Another shortwave
upstream drops down off the Eastern Russia region into the
Southwest Alaska area. This synoptic feature moves eastward before
developing into a closed upper level low over the northern Gulf
by Sunday evening before elongating, and extending into the lower
Southeast Panhandle region by Tuesday morning. As these
aforementioned synoptic features track through the AOR, look for
the shortwaves to produce a showery weather regime. Therefore, the
forecast confidence is below average with the continued timing,
and intensity issues with the closed upper level lows/troughs.
Otherwise, look for continued cooler, and wet conditions through
the early part of next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

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