Small Craft Advisory 630, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
402 AM AKDT WED AUG 10 2016

.ANALYSIS AND UPPER LEVELS...

A large upper low over the the western half of mainland Alaska
remains stationary this morning, with numerous disturbances
bringing varying coverage of showers across the southern Alaska
region. A second upper low is moving slowly east over the central
Bering, with the strongest disturbance on the south side of this
low moving across the southeastern Bering and through the Eastern
Aleutians toward the Alaska Peninsula. An active jet streak
pattern persists from the western Bering and Western Aleutians
extending east mainly through the Pacific coastal waters and Gulf
of Alaska toward the Panhandle region.

&&

.MODEL DISCUSSION...

Models are good agreement through the short term, with better
agreement now for late week with the remnants of Tropical Storm
Omais moving east across the Bering Sea toward the Bristol Bay
region. The higher resolution models were favored for the first 48
hours or so in the timing of any gaps winds and showers. After
this, the forecast package leans more towards the GFS and ECMWF,
which are now in very good agreement for the late week period
across the Bering.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Moist southwesterly flow aloft will continue over the area into
Thursday as the upper level low remains over western Alaska. This
will keep a fairly cloudy and showery regime over the area, with
the best chances for precipitation over the Susitna valley area.
The system currently over the southeast Bering Sea and Alaska
Peninsula/Eastern Aleutians will round the base of the western
Alaska low early Thursday and work its way into south-central
Alaska during the day. This system will bring a period of
stratiform rain to the coast and increased chances of rain to most
of the south-central mainland later Thursday through Thursday
night.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The weakening stacked low remains stationary over the Lower
Kuskokwim Valley, and will continue to control the weather for
the next several days until the next system approaches the area
from the west Friday Morning. The current system will keep a
persistent moist southwest flow moving off the Bering Sea, and all
the way up against the Aleutian and Alaska Ranges. There will be a
enough instability to support isolated thunderstorms along the
Kuskokwim Mountains and Alaska Range this afternoon and evening.

Prior to the next system approaching from the west, much of the
Southwest mainland could see a brief break from the wet weather
on Friday morning, as the upper level low breaks apart and moves
out of the area. There will likely be plenty of cloud cover as the
flow will remain mostly onshore, along with enough residual
instability for one more round of isolated thunderstorms along the
Alaska Range Friday afternoon and evening. The next system looks
to start tracking inland by late Friday bringing more widespread
showers back to the area.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The forecast for the Bering Sea and Aleutians will be
characterized by two lows tracking through the area through the
rest of the week. The first is currently tracking eastward into
the Central Aleutians, and will dissipate as it moves over the
Central Aleutians today. The second system will be the remnants
of Tropical Storm Omais, and it will move into the western Bering
Thursday. As it tracks east through the end of the week its
impacts will be primarily confined to gale force winds and an
increase in rain over the Bering. The exception will be the
Western Aleutians that will see gale-force winds Wednesday night
into Thursday, while the winds for the Central and Eastern
Aleutians look to stay just below gale-force late Thursday and
Friday as the low passes.

&&

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

Heading into Saturday a Bering storm system, within a broad
longwave trough over Alaska and the Bering, slides to the
southwestern Gulf and continues slowly eastward through the
weekend. To the west, a north pacific ridge amplifies northward
toward the western Bering. This set up allows multiple shortwaves
to dive down from the northern Bering and then wrap around the
base of the the trough in the gulf. This synoptic regime keeps the
highest chances for rain and stronger persistent winds across the
eastern half of the Bering and along the Alaska Peninsula. The
gulf coastal areas will stay in a wetter pattern with inland areas
staying in a showery pattern. Models are in very good agreement
with this long range forecast so a blend of the GFS and ECMWF,
including ensemble means, was used to update the forecast Saturday
through Tuesday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES...177 178.
FIRE WEATHER...NONE.

&&

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