Small Craft Advisory 868, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
456 AM AKST Mon Nov 5 2018

.ANALYSIS AND UPPER LEVELS...
Ridging over mainland Alaska still dominates, though it is
starting to collapse and begin its slow progression east. A
shortwave riding up over this ridge is reflected as a weak front
at the surface and is pushing through southwest Alaska, bringing
some light precipitation with it. Meanwhile, a strong low is
barreling into the western Bering Sea with storm force winds
behind its associated frontal systems. Finally, a pressure
gradient setup is present along the Chugach mountains is causing
strong localized winds. Offshore winds are present through
Whittier, Thompson Pass and areas around Valdez.

&&

.MODEL DISCUSSION...
Models continue to handle the overall pattern decently through
about midweek. They have been consistent on the incoming low into
the Bering Sea, so high confidence in the forecast with that
system. The latest run of models has them in better agreement with
the low moving into the Gulf of Alaska on Wednesday. Yesterday
there was disagreement between the GFS and other models in the low
track, but today all major model are showing the low moving into
the Gulf of Alaska, with an occluded front impacting the coast.
Therefore, confidence as increased with this system.

&&

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

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
High pressure will remain over the Southcentral mainland through
Tuesday afternoon. Dry and mostly clear conditions will continue
as a result. The surface pressure gradient will relax today,
allowing the gap winds to diminish and/or end. The upper level
high will move east Tuesday night as a trough approaches from the
west. A strong low on the southern end of the trough will move
into the southern Gulf Tuesday night. The leading front will bring
precipitation to Kodiak Island beginning late Tuesday afternoon
or early evening. Precipitation will surge northward to the Kenai
Peninsula Tuesday night, with the highest chances on the eastern
and southern portions of the peninsula.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Currently a flat upper level ridge extends from the Alaska
Peninsula to the northeast into Southwest Alaska. A weak warm
front along the Kuskokwim Delta coast which has been bringing
some very light precipitation will push very slowly east in
advance of the front moving into the eastern Bering but will stall
along the coast through this afternoon. The more organized
incoming Bering front will reach the Kuskokwim Delta coast this
evening and then swing inland over the Kuskokwim Delta late
tonight through Tuesday morning. The front will weaken and shear
apart as it continues east over the Greater Bristol area and
Kuskokwim Valley Tuesday afternoon through Tuesday night as as a
developing frontal wave to the south deepens and tracks into the
Southwest Gulf. Upper level troughing on Wednesday will keep
Southwest Alaska cool with isolated to scattered showers tapering
off from west to east as a transient ridge builds along the coast
Wednesday night in advance of the next Bering frontal system.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A strong Kamchatka low will bring a small swath of storm force
winds and broader area of Gales into the western Bering as it
tracks east today. Additionally, the cold air aloft and strong
instability accompanying the upper low will bring the potential
for some isolated thunderstorms along with it. The low will
become vertically stacked and then gradually weaken as it curves
to the northeast tonight through Tuesday. The next incoming
frontal system will reach the western Aleutians early Wednesday
morning, continue east to into the central Bering Wednesday
evening and reach the eastern Bering early Thursday morning.

&&

.LONG TERM FORECAST (Days 3 through 7)...

At the onset of the forecast period, there is a storm southeast
of Kodiak and an organized system east of Kamchatka. Models seem
to be improving and converging on both the low in the Gulf Of
Alaska and the new low in the Bering. There are some minor
differences with timing and intensity for both lows, but there is
a confidence boost for the longterm. Both of these storms will
bring another round of enhanced/gusty winds and a well organized
precipitation shield. Thursday the surface low for the gulf storm
will be just south of Middleton Island moving northeast. An
inverted trough will develop over Prince William Sound and into
the Copper River Basin. By Friday, the the surface low will have
rapidly weakened and pushed off to the east. In the wake of the
frontal passage ridging will build over the Gulf of Alaska. The
main weather producer with the the frontal boundary pushing across
the Aleutians/Bering and into southwest AK by the weekend. There
is a secondary impulse on the back side of the Bering low which
the models ping into.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Storm Warning 411.
Gale Warning 412, 413, 414, 177, 178, 179, 181, 185.

&&

SYNOPSIS AND MODEL DISCUSSION...BJB
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR
LONG TERM...PS