Gale Warning 410, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
438 AM AKDT Sat Sep 14 2019

.ANALYSIS AND UPPER LEVELS...

The strong upper level jet core and 500 mb low associated with
the widespread rain over the past couple days has moved well
south of mainland Alaska. A weak shortwave ridge in its wake is
bringing clearing skies this morning to much of Southwest Alaska,
while radar is still showing a few scattered showers over Prince
William Sound on the northern fringes of the departing surface
low. Another strong upper jet core in the western Bering is
leading to the development of a surface low which will bring
unsettled weather to the area this weekend.

&&

.MODEL DISCUSSION...

Synoptic models remain in good agreement in the short term. Though
there are subtle differences in the surface low's progression on
Sunday, confidence remains high regarding accumulating rainfall.

&&

.AVIATION...

PANC...VFR conditions are generally expected to persist through
Saturday morning. However, patchy fog is likely around the
airport which could possibly lead to brief periods of MVFR and/or
IFR conditions through approximately sunrise this morning. Light
winds will continue.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2/Today
through Sunday night)...

A weak ridge of high pressure will build
into Southcentral today. Weak short-waves moving over top of the
ridge will keep a few clouds and showers in the forecast,
primarily over interior areas of the Susitna Valley and Copper
River Basin. Otherwise, expect decreasing cloud with some
afternoon sunshine and above normal high temperatures in the lower
to mid 60s.

The dry weather will be short-lived, with progressive upper level
flow steering another storm eastward across the Bering Sea today
and into Southcentral on Sunday. This looks like a soaker for
nearly all of Southcentral with good upper level dynamics and a
abundant moisture feeding into this system. Rain will begin on
Kodiak Island late Saturday night and spread north and east
across Southcentral during the day Sunday.

Similar to the last storm, a triple point low will form over the
northwest Gulf. However, with the upper level low barreling
eastward, the surface low will follow suit, tracking eastward
across the northern Gulf. There will be some southeasterly gap
winds ahead of the low and front on Sunday. However, overall low
level flow does not look very strong and do not expect downslope
flow to play much of a role. In addition, with the relatively fast
movement of this system, wind directions will change quickly
throughout the day, minimizing the amount of time of cross barrier
flow in any given location.

Rain will gradually break up into showers Sunday night into Monday
as the storm exits to the eastern Gulf. The presence of a high
amplitude ridge upstream over the eastern Bering Sea will lead to
strong and gusty westerly winds across the western Gulf and
Kodiak Island beginning Sunday afternoon. Offshore flow will then
develop over Southcentral Sunday night, with locally gusty winds
along the Gulf coast and Prince William Sound.

&&

.FIRE WEATHER...

Most of Southcentral will see wetting rains with the next storm
moving in on Sunday. The Tokaina fire is one specific area which
may not see a wetting rain. There will be a bit of downslope flow
initially, then the best upper level dynamics will move quickly
through.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1-3: Sat-Mon)...

As the weak onshore flow and fog dissipates across the Kuskokwim
Delta and Southwest Alaska this morning, dry conditions and
clearing skies will give the region a break in active weather
today. The rainfall and stronger winds will make their return
tonight into tomorrow morning as a new front associated with a
Bering makes it way to the Southwest coast. This system, bringing
heavy rain at times, will move inland and weaken through Sunday
afternoon before quickly exits into Southcentral. A few showers
may linger around Southwest on Monday, but overall should remain
dry with cloud cover decreasing.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1-3: Sat-Mon)...

A low over the western Aleutians this morning will bring small
craft advisory winds as it moves across to the eastern Bering by
Sunday morning. Gale force winds are forecasted along the AKPEN
early Sunday before winds weaken into Monday morning.

The next system will make its way to the western Aleutians and
Bering by Sunday afternoon. Although there is less certainty in
the exact speed and strength of this storm, there is better model
agreement today that there will be small craft advisory winds
accompanying this system as it moves into the central Bering by Mon
afternoon.

&&

.MARINE (Days 3 through 5)...

Low pressure moving through the forecast area Sunday into Monday
will bring small craft advisory level winds and seas to the Bering
Sea. A low forming in the Gulf will bring gale force winds to the
Gulf on Monday. Monday night into Tuesday there is uncertainty
with a North Pacific low and whether it will hold in the North
Pacific or track north into the Bering. Confidence is low with
this system as there is large model disagreement on what the low
will do.

&&

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

The long term is steeped with uncertainty as the forecast heads
into Tuesday. The main factor that is creating uncertainty is a
cut off low south of the western Aleutians. Monday night into
Tuesday a trough will move through the Bering from west to east
and there is disagreement amongst the models on how this will
interact with the cut off low. Some of the models, including the
GFS, have the low phasing with the trough which will bring a
system over mainland Alaska resulting in widespread rain for
southern Alaska on Wednesday. However, other model solutions,
including the EC, have the trough moving through without impacting
the cut off low resulting in a significantly drier setup for the
southern mainland. Confidence with any of these solutions is low
with how widespread the various models solutions are.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AP
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...DK