Small Craft Advisory 349, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
446 AM AKDT Sat May 4 2019

.ANALYSIS AND UPPER LEVELS...
Several areas across Alaska are waking up to a showery pattern
this morning. Scattered rain showers across Southcentral can be
seen on radar imagery associate with an upper level shortwave
positioned over the AKPEN. A weak surface low in the Gulf south of
Middleton Island is also showing precipitation and increased
cloud coverage on IR satellite imagery. The central Aleutians and
Bering are seeing a stronger band of rain and gusty winds as a
front associated with a mature low, positioned over Shemya,
progresses eastward towards the eastern Aleutians and AKPEN
throughout the morning. Southwest Alaska is seeing a drier pattern
this morning, with isolated showers possible mainly near Bethel.

&&

.MODEL DISCUSSION...
The global models are in good agreement with the placement of the
synoptic features through Monday 12z. There are some minor
differences in the handling of the precipitation associated with
the next frontal boundary crossing the Bering and the Aleutians.
Some of these issues are timing related, but additionally, the NAM
looks more convective in the post frontal environment. The GFS
ensemble members at MSL pressure are tightly grouped through 12z
Sunday which is consistent with the operational runs of the
Canadian, GFS and ECMWF. The confidence level is above normal
through 12z Sunday.

&&

.AVIATION...
PANC...Looking at the latest GOES satellite image confirms
widespread cloud coverage over the northern portion of the Cook
Inlet and Anchorage Metro area. These are the remnants of a
decaying upper low and the clouds are at layered and at different
heights. As of 10z the cig at PANC was at 8,500 ft while the cig
at PAMR was at 6,500 ft. Expecting VFR conditions and light winds
will persist this TAF package.

&&

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

The shortwave moving through Southcentral Alaska front he
southwest is located in the Matsu-Valleys through Prince William
SOund early this morning. This will keep the majority of the
precipitation in the Copper River Basin for today. The cold air
aloft is evident with this wave as the snow level is low enough to
bring accumulating snow to the Chickaloon Pass area of the Glenn
highway. Eureka has reported numerous hours of snowfall with
visibility under one mile overnight.

The next front will move over Kodiak Island from the south
overnight and push into Southcentral Sunday. This front will bring
Gale force winds along the north Gulf coast and ample rainfall to
coastal regions. For Sunday, it looks like the cross-barrier flow
will be sufficient to cut off most of the rain on the leeward
side of the mountains. Strong Southeast winds are expected through
channeled terrain especially in the typical areas such as
Turnagain Arm, Knik River Valley and along the Copper River. It
also looks like gusty winds will make it into the Anchorage Bowl
Sunday into Sunday evening. On Sunday night, the downsloping
should lessen and rain will become more likely for the leeward
sides of the mountains as well.

&&

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

Isolated showers will continue over the Kuskokwim Delta/Coast as
southwest flow persists today. Farther south in the Bristol Bay
area, a ridge building over the eastern Bering has cut off
precipitation for the day with mostly clear skies. A low currently
centered roughly 150 miles southwest of Attu will slowly drift
eastward today into tomorrow. A triple-point low rotating around
the western periphery of that parent low will bring a transition
to wetter, windier weather Sunday. Expect gusty winds over the
Aleutian Range early Sunday, then as the meso low shifts northward
into Bristol Bay, winds will ramp up in Kamishak Bay and to the
northwest across the interior Bristol Bay region towards the
Kuskokwim Mountains. There's uncertainty with precipitation in the
lee of the Aleutian/Alaska Range; dry downslope winds should limit
precipitation, but expect upslope flow to enhance precip in the
Kilbuck/Ahklun Mountains and Nushagak Hills.
Southerly/southwesterly winds will diminish as the low progresses
towards Nunivak Island late Sunday into Monday.

&&

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

A mostly benign pattern is on tap for the next few days. A gale
force boundary over the central Aleutians will weaken to sub-gale
force this morning, and continue its trek eastward as the
associated low currently southwest of Attu progresses east.
Precipitation will continue along the front, with scattered
showers behind the front. Expect broad cyclonic flow over the
Bering through Sunday. Along the southern coast of the eastern
Aleutians and AKPEN, a triple point low will bring small craft
winds and seas as it pushes northward against the chain tonight.
Winds will shift to southerly and sub- advisory as the low moves
into Bristol Bay by mid-day Sunday.

&&

.MARINE (Days 3 through 5...Mon through Wed)...

A low that gradually moves along the Aleutian Chain this weekend
will eventually center itself over the Pribilof Islands by Tue
and will remain nearly stationary through Wednesday. This will
generate northerly flow and a showery regime over the western
Bering. On the eastern side of the low, southerly flow will
prevail over the Gulf. This will allow a series of North Pacific
lows to track into the Gulf through Wed. Easterly flow along the
northern Gulf coast will briefly generate gale force winds over
the Barren Islands and Hinchinbrook entrance Sun morning through
Sun evening, diminishing to small craft by Mon morning.
Thereafter, it looks like a series of lows will move through the
Gulf through Wednesday. Gale force winds are possible, especially
along the northern Gulf coast. Exact track and timing is not
certain at this time, but there is higher confidence this pattern
will be in place through at least mid-week.

&&

.LONG TERM FORECAST (Days 4 through 8...Tue through Sat)...

There is a high level of confidence that a pattern change will be
underway for next week across the northern Gulf coast and Kenai
Peninsula. The two main features that models reflect consistently
are an area of low pressure in place over the eastern Bering and
an area of high pressure over the southeastern Gulf. A cooler,
wetter pattern is very likely as both of these systems work to
advect moist southerly flow over Southcentral. However, there is
high uncertainty in the orientation of the upper level jet. This
yields much lower confidence in where the bulk of the moisture
will be directed and how much will be received. Generally,
unsettled weather conditions can be expected across the southern
Mainland through Saturday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale 130 131.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AH/PJS
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MM
MARINE/LONG TERM...KO