High Surf Advisory 1, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
644 AM AKST Tue Nov 6 2018

.ANALYSIS AND UPPER LEVELS...
The upper level ridge continues to be the main weather feature
for mainland AK. It is currently sliding eastward and is located
over eastern Alaska, extending up through the eastern Interior all
the way into the Arctic. Behind it, an upper level low with a
broad trough encompasses much of the Bering Sea and is approaching
the West Coast of the state. Another upper level low is moving
northeast through the North Pacific and approaching the Gulf of
Alaska.

The upper level high continues to keep temperatures cold at the
surface for much of Southcentral Alaska. Meanwhile, the broad
upper level trough is supporting a weak frontal system that is
pushing through Southwest AK, bringing rain and low ceilings with
it. The upper level trough is also supporting a stronger low out
in the Bering Sea that has gale force winds associated with it.

&&

.MODEL DISCUSSION...
Models are in good overall agreement for the next couple of days.
As the previous discussion noted, models are locked on the system
in the Bering, so a consistent forecast continues there. Models
differ from yesterday with the low moving into the Gulf of Alaska,
but have come into agreement enough to start to hone the forecast
for Thursday into Friday. All models are sending precipitation
into coastal areas of Southcentral, so we upped PoPs and QPF for
areas along the coast. Fine tuning will be needed over the next
couple days.

The next low in the Bering Seas presents the same difficulties as
yesterday, with the EC still moving the system farther south
faster than other guidance.

&&

.AVIATION...
PANC...VFR conditions and light winds will largely persist.
However, some low level stratus is lingering along Knik Arm and
pushing into the airfield this morning. The stratus is expected
to clear by late morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
High pressure will be over the mainland through tonight. This high
will slowly slide east as a trough approaches from the west. A low
approaching from the south will begin to interact with the trough
later today as it moves into the southwest Gulf. The leading
front will bring precipitation and increasing winds to Kodiak
later today, and the Kenai Peninsula tonight. The front will reach
the northern Gulf coast Wednesday morning, with the low at this
time southeast of Kodiak Island. The exact track of this low is
still up for debate, and precipitation amounts are still in
question. By Wednesday night the low becomes fully entrained in
the upper trough. The axis of the trough will be near Cook Inlet
by early Thursday morning, which puts much of Southcentral in a
favorable position for at least a chance of some precipitation.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The frontal system along the Kuskokwim Delta coast will swing
slowly inland today. The front will reach the Kuskokwim Valley
and Greater Bristol Bay area this afternoon and evening and then
stall overnight along a line running from Sleetmute to Dillingham.
As a surface low and accompanying frontal system move into the
western Gulf late tonight through Wednesday morning, the stalled
front will begin drifting slowly east while being reinforced
slightly as a deformation band along the northwest side of the
low. Upper level ridging will build in Wednesday night and shift
inland Thursday morning before the next incoming frontal system
reaches the coast Thursday afternoon and swings inland Thursday
night.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The surface low currently to the west of Saint Matthew Island will
continue tracking off to the northeast, reaching the Seward
Peninsula late tonight. Cool, unstable troughing with general
westerly flow across the Bering today will be briefly replaced by
ridging building in from west to east tonight through Wednesday
ahead of the next incoming frontal system. This front will reach
the western Aleutians early Wednesday morning, the central Bering
and Aleutians Wednesday afternoon and evening and the eastern
Bering Thursday morning. The strong associated parent low will
track into the western Bering Wednesday night bringing strong cold
air advection and an area of storm force winds with it to the
offshore waters.

&&

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

An active pattern will be on tap for the west domain Thursday to
Monday. At the onset of the forecast period, there is a storm
south of the Aleutian chain and a mature system with a triple
point low in the Bering. Additionally, there is a disturbance near
Kodiak. There are some minor differences with timing and the
tracks of of the lows as early as F72 and F96. However, as time
elapses, the differences significantly amplify. With the longwave
trough in place over the Bering and the North Pacific, we are confident
in the level of persistent unsettledness for the Bering, the
Aleutians and Southwest Alaska. However, given the lack of run to
run continuity there seems to be more uncertainty in the long term
for Southcentral Alaska including Prince William Sound. Waiting
for the details to flesh out beyond F96.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE....Gale Warning 411, 412, 413, 150, 177, 178, 181, 185,
351, 352, 119, 120, 131, 132.

&&

SYNOPSIS AND MODEL DISCUSSION...BJB
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR
LONG TERM...PS