Small Craft Advisory 629, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
408 AM AKDT Thu Aug 16 2018

.ANALYSIS AND UPPER LEVELS...
The longwave pattern features a deep trough covering most of
mainland Alaska and the Aleutians. There is a dome of high
pressure that has begun to move out of NE Russia and into the
Central Bering. There are numerous weak shortwaves across
Southcentral, the interior of Alaska and over Southwest Alaska.
The most organized disturbances are near the AKPEN and south of
the Central Aleutians. The West Pacific to the North Pacific
Corridor has become very dynamic. The radars on Kenai and
Middleton Island continue to ping into weak returns/light
precipitation.

.MODEL DISCUSSION...
Models have come into better agreement with the series of storms
in the West and North Pacific. The GFS/NAM are in good agreement
at both the surface and at 500 mb. The model consensus is more
cloudy/wet weather for Southcentral Alaska, Kodiak and the AKPEN
for today. Friday is still on track to be the driest day of the
week for the Anchorage Metro Area with the possibility of the dry
conditions lingering into Saturday.

&&

.AVIATION...
PANC...VFR conditions expected. The pattern is going to remain
unsettled, expect clouds and pockets of precipitation for PANC for
the forecast period. The Kenai Radar/PAHG has detected a band of
precipitation over the northern Cook Inlet.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Widespread showers currently around the Cook Inlet region should
wane this morning as the upper low shifts northeastward. However,
weak stability, abundant moisture, and lingering cyclonic flow
will keep at least a chance of showers through the morning and
early afternoon. The best chance for showers this morning will
remain around the north Gulf coast, more under the influence of
the upper low. The same conditions will stick around through the
afternoon and evening hours, but forcing in non-existent, which
will lead to diurnal instability. The resultant shower activity
will mainly be focused near the mountains, but a stray shower
can't be counted out in most areas. Friday will be drier,
including a reduction in cloud cover and sunshine making a cameo.
The next real weather maker will be a front approaching from the
southern Gulf over the weekend. Temperatures will be right around
climatological normal and winds relatively light for the forecast
period.

&&

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

Low pressure southwest of Cape Newenham will continue to slowly
drift south through the eastern Bering today. The weak onshore
flow with this system will keep coastal regions of Southwest
Alaska and the Alaska Peninsula cool and showery with a few breaks
of sunshine for interior locations. Weak ridging will build over
SW AK for Friday as the low moves into the North Pacific and
becomes absorbed by a second system moving north. Areas of fog are
possible Friday morning under this ridge with light winds and
lingering low-level moisture. Clouds and precipitation will begin
to overspread the Alaska Peninsula Friday as a front associated
with a developing area of low pressure pushes over the region.
East to southeast winds will also increase ahead of the low, with
gales developing along the AKPEN coast and in Bristol Bay by
Friday evening. Southeasterly gap winds will also increase Friday
and linger through Saturday evening. Rain will push into SW AK by
Saturday with some initial lee-side drying (downsloping) due to
the southeasterly winds. Winds and rain diminish for Sunday as
the front weakens.

&&

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

A compact, vertically-stacked low will continue to produce gusty
northerly winds and showers across the eastern Bering as it drifts
south toward Cold Bay. By Friday morning, this low will become
absorbed by a second developing North Pacific low. This system
will push a front towards the AKPEN bringing gale-force sustained
winds with storm-force gusts along the eastern Aleutians through
Saturday evening. This system will also have a deep sub- tropical
moisture fetch associated with it allowing for another round of
moderate to heavy rain across the Eastern Aleutians, Alaska
Peninsula, and eastern Bering through Saturday as the front lifts
north and weakens by Sunday.

Farther west, high pressure will dominate the weather pattern over
the central Bering and Aleutians through the weekend. Stable air
underneath this ridge will produce areas of low stratus and fog
across the central Bering and Pribilofs. A warm front associated
with a developing Kamchatka Low with move across the western
Aleutians Friday evening and into the western Bering Saturday,
bringing rain and gusty winds. Conditions will remain unsettled
over the western locales through Sunday as the trailing cold
front moves through.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The long term beginning Friday night starts with a North Pacific
low sandwiched between two ridges. The first ridge will be over
the eastern Gulf while the other is over the central Bering. There
is some discrepancy between the models on the exact position of
the low and subsequently its front, but the general consensus is
that the front will bring rain to the Alaska Peninsula and Kodiak
Island Friday night. Through the weekend the system will slowly
track north spreading rain to the southern mainland with the
heaviest amounts along the north Gulf coast and Alaska Peninsula.

Meanwhile out west, another system will push into the Bering over
the weekend as the central Bering ridge breaks down. Early next
week the upper level low centers of the two main lows look to
merge into a broad area of low pressure over the Bering with
ridging off to the east. This setup would keep a rainy pattern
for the region into mid next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...None.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...ML
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TM
LONG TERM...DK