Area Forecast Discussion
Issued by NWS Anchorage, AK

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795
FXAK68 PAFC 170059
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
459 PM AKDT Mon Oct 16 2017

.ANALYSIS AND UPPER LEVELS...
A strong zonal subtropical jet (175kt at 300mb) is centered south
of the Aleutian chain, maintaining a storm track over the
southern tier of the Alaska region. A deepening low along the
western Aleutians has occluded and is about to become vertically
stacked. Expect triple point development as the more favorable
dynamics shift downstream. Gale force winds are being observed in
Atka and Adak out ahead of the warm front, with a few gusts up to
storm force. Satellite scatterometer winds indicated storm force
winds in the cold sector of this system to the south of the far
western Aleutian islands.

Looking downstream of this storm, quiet conditions dominate most
of the rest of the forecast area from the eastern Bering and
Southwest Alaska to Southcentral and the Gulf. There are some weak
features to speak of. An upper level short-wave approaching the
Southwest Alaska coast is producing a few showers out ahead of it.
Over in the Gulf, a weak vertically stacked low over the northern
Gulf is slowly exiting to the east, with a few showers wrapping
westward across southeast Prince William Sound.

&&

.MODEL DISCUSSION...
Models finally seem to have a good handle on the storm along the
Aleutians and show a similar solution as it heads eastward. There
are some minor differences with triple point low development south
of Kodiak Island Tuesday morning and continuing as the low
crosses the southern Gulf Tuesday night. The 12Z NAM is the only
real outlier with a farther south position of the occluded front.
The other solutions show the same general idea and lead to
increasing confidence in a Gale force front affecting the Gulf and
Kodiak Island waters.

&&

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

&&

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

The pattern has remained fairly stagnant over the last couple of
days with persistent cooling temperatures, offshore flow, and
clearing skies over most of Southcentral. Overnight lows will
continue to cool a few degrees lower each night as the atmosphere
decouples. The exception to this remains the Prince William Sound
area eastward, where southerly flow ahead of a weak northern Gulf
low is pushing a maritime airmass inland. The low will drift
southeastward and dissipate tonight, bringing an end to most of
the residual showers lingering along the coast. There is a chance
a few light showers could move into western Prince William Sound
tomorrow if the low takes a little longer to dissipate, however
the general model consensus favors a drier solution. Offshore
winds throughout the Gulf Coast will briefly slacken overnight
through tomorrow morning as the pressure gradient weakens with the
departure of the low.

Tuesday morning, a front associated with a North Pacific low will
swing into the southwestern Gulf. This will spread rain and a
swath of small craft to gale force winds from the Alaska
Peninsula and Kodiak Island area through the southcentral Gulf of
Alaska Tuesday. The front will pivot through the Gulf Tuesday
night and exit to the northeast Pacific Wednesday, keeping it`s
associated precipitation to the south of the northern Gulf Coast.
Increased cold air advection behind the low will lead to gusty
offshore winds through terrain gaps throughout the northern and
western Gulf Coast Tuesday night through Wednesday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
Mostly clear and cool weather will persist over southwest tonight
as a transitory shortwave ridge briefly builds overhead. Fog will
likely develop again in the morning hours over the Kuskokwim
Delta and River Valley with light winds and ample moisture at the
surface. A strong low over the Aleutians will stay to the south
keeping the area mostly dry, though cloud cover from the system
will overspread most locations tomorrow. Northerly flow on the
backside of the low will draw cold air south on Wednesday leading
to colder temperatures and the development of instability
rain/snow showers during the day, especially near the coast.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
The main focus for the forecast period will be a storm force low
currently centered just north of Adak. This system is being
supported by a very strong westerly 185 kt jet to the south over
the Northern Pacific, and will guide the storm center east across
the Aleutians and eventually southeast into the open Pacific
waters by Wednesday. Main impacts from this system tonight and
tomorrow will be strong gale force southeasterly winds associated
with the warm frontal passage and storm force northwesterly winds
on the backside of the storm, which will be enhanced by cold air
advection from the north. On Wednesday the system will have
departed the region as cold northerly flow overtakes the Bering
with an upper level ridge building in from the west. The next
system approaches the Western Aleutians by Wednesday afternoon.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The mid and long term forecast beginning Wednesday night has cold
outflow winds over the southern mainland and a low tracking east
along the Aleutians. There is good agreement amongst the models
with this low until it moves into the Gulf Friday night. At this
point there are differences in how it approaches the southern
mainland. Some of the solutions bring the majority of the
precipitation to the north Gulf coast while downsloping over the
northern Cook Inlet area. However, there are some solutions that
would bring snow to the Anchorage area. At this point there
remains too much uncertainty for a high confidence forecast one
way or the other.

By early next week there is some agreement that the remnants of
Typhoon Lan could track towards the western Bering, but there
remains huge differences on its strength and position.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale 132 150 155 165 170 171 172 173 175 178 351 352 411
         413 414.
         Storm 174 176 177.
&&

$$

SYNOPSIS AND MODEL DISCUSSION...SEB
SOUTHCENTRAL ALASKA...RD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KVP
LONG TERM...DWK



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