Small Craft Advisory 785, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
408 AM AKDT WED OCT 5 2016

.ANALYSIS AND UPPER LEVELS...
Quiet weather continues over much of southern Alaska this morning
with surface high pressure in place over much of the area and a
fairly stagnant upper level weather pattern as well. A very weak
upper level disturbance is helping form an altostratus deck from
the Kenai Peninsula northward through the Susitna Valley, though
the 00Z Anchorage sounding shows there's more than enough dry air
in between to prevent any potential precipitation from being a
problem. An area of much lower stratus is also noted over the
southern Kenai Peninsula as well, as radiational cooling helps
allow for condensation of available water vapor in the air. The
developing cloud deck has squelched further temperature drops as
it has drastically limited the effectiveness of the radiational
cooling process.

For Southwest Alaska, an upper level front is slowly pushing
eastward through Bristol Bay and the Kuskokwim Valley. Plenty of
dry air in that area is keeping any precipitation echoes confined
to locales near the coast, especially west of Bethel. The cloud
cover is holding temperatures in the 40s from the Kuskokwim Delta
southwestward through Bristol Bay. The winds are also light with
no operationally significant surface features to key in on.

All of the interesting weather action is occurring out over the
Bering Sea and Aleutians this morning as a strong low south of
Attu and Shemya approaches the western Aleutians. Gale force winds
are being reported from Shemya and Attu eastward though the
central Aleutians. Several persistent thunderstorms are producing
lightning between Shemya and Adak as a more unstable air mass
wraps around the low pressure center. The low is drawing its
energy from a 90 kt jet streak positioned ahead of a digging
trough in the upper level flow. Behind the trough is a much
stronger 150 kt jet streak moving out of Russia and northern
Japan, which will be the animus for potentially stronger
extratropical development in a couple days.

&&

.MODEL DISCUSSION...
Models remain in good agreement with no impactful discrepancies
through the end of the week. Guidance continues to agree on
keeping Southcentral Alaska in more of a dry and warm pattern
through the end of the week, as ridging continues to build into
and persist over the area. Whereas out west, the models continue
to remain in strong agreement with a low-end storm force low
moving into the Bering Sea Today and Thursday. Models also remain
in good agreement with the strength and track of the post-
tropical remnants of former Super Typhoon Chaba as starts to
impact the Western and Central Aleutians Thursday Night into
Friday, then track into the Central Bering by Saturday morning.
Forecast confidence remains high throughout the short-term.

&&

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

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
One last upper level short-wave over Southcentral will exit to
the south today through tonight, helping to clear out most of
the remaining clouds. A few clouds may linger across the far
southeast Copper River Basin with an upper low sitting near
Yakutat. Wednesday through Wednesday Night a ridge over northern
Alaska will merge with a building ridge ahead of the strong
Aleutian low. The end result will be a strong blocking ridge
centered over Mainland Alaska. This will provide Southcentral with
a prolonged period of clear and dry weather with temperatures
fairly close to seasonal norms.

&&

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

A weakening and shearing out front will keep isolated to scattered
showers along the Kuskokwim Delta coast this morning before
diminishing. The main story, thereafter, will be strengthening
high pressure aloft through Friday as a strong blocking high forms
over interior Alaska. Skies will clear out tonight and Thursday as
the low level flow becomes more southeasterly and the high builds
in aloft.

&&

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

A low end storm-force low and associated warm front is moving
slowly east across the western and central Bering Sea this
morning. The front will move toward the Pribilof Islands this
evening then stall and slowly weaken across the Eastern Aleutians
through Thursday evening. Some local gusts to 45-60 MPH will
occur from Atka to the Pribilofs and Unalaska as the front moves
over.

Attention quickly turns to the western Bering Sea as the remnants
of former Super Typhoon Chaba undergoes strong extratropical
transition Thursday before moving into the Western Aleutians
Thursday evening as a storm force warm seclusion. The main impact
will be winds close to 55 knots and seas to 40 ft along the
Pacific side across parts of the Western Aleutians.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Guidance continues to get a better handle on what the remnants of
Super Typhoon Chaba will do as it approaches the Western
Aleutians. With all the models holding strong high pressure over
mainland Alaska from Thursday through the weekend, they all keep
the remnants of Chaba well to the west of mainland Alaska. It
looks to move into the central Bering late Friday and then turn to
the northwest as it weakens through the weekend. There is also
better agreement with the winds associated with this storm that
look to bring storm force winds to marine areas on the Pacific
side of the Western Aleutians Thursday night and Friday. For
mainland Alaska the aforementioned high pressure will keep the
skies mostly clear through the weekend.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Storms...173-176 412 413
 Gales...155 165 177 178-181 185 414.

&&

SYNOPSIS AND MODEL DISCUSSION...TP
SOUTHCENTRAL ALASKA...SB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
LONG TERM...DEK