Small Craft Advisory 854, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
507 PM AKDT Thu Nov 1 2018

.ANALYSIS AND UPPER LEVELS...
The upper level pattern today features a weakening omega block
with an area of high pressure in place over much of the state and
two areas of low pressure on each side: one over the Panhandle and
the other situated just south of the central Aleutians. A strong
upper level jet stretched across the North Pacific has max values
near 160 knots.

Satellite imagery shows mostly clear skies across Southcentral
with high clouds present over Southwest Alaska in advance of a
leading front associated with the 965 mb surface low near the
central Aleutians. As has been the case for the last couple of
days, low level stratus and fog persists in the Copper River Basin
in response to subsidence associated with the high pressure.

&&

.MODEL DISCUSSION...Models remain in good overall agreement over
the forecast area into the weekend. There is some minor differences
in the speed of the low in the Gulf of Alaska Sat and Sunday as it
moves eastward. This will be the main synoptic feature to watch
for on upcoming model runs.

&&

.AVIATION...VFR conditions and light winds will persist. There is
some fog lingering in Turnagain Arm and Knik Arm. With high
pressure building overhead conditions look ripe for expansion of
the fog overnight. However, with very weak flow, don't expect the
fog to move very far, so have kept any mention out of the
terminal forecast. Will keep a close eye on how this evolves this
evening and update if fog is growing more than expected.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...
Shortwave ridging will move in over Southcentral tonight, and
with weakening pressure gradients and cold high pressure in
place, this is a good setup for local valley fog as well as fog
along Knik Arm and down Turnagain Arm. While the Copper Basin has
completely cleared out, it is likely that at least some stratus
and fog will also develop overnight. Gap winds along the coast
will remain gusty into Friday morning then weaken.

An occluded frontal zone will move into the Gulf Friday morning
and spread rain and gale force winds into Kodiak before stalling
on the North Gulf Coast Saturday morning and falling apart.
Besides coastal rain and some higher elevation snow, the front
quickly moves east Saturday evening with drying and clearing
again by Sunday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
High pressure dominates southwest Alaska and is keeping most of
the cloud cover away. This will last until Friday morning when a
front will move into the Bristol Bay area from the southwest. The
front will stall over the area and bring precip around Bristol
Bay into Saturday night. The front will bring an influx of warmer
air to the coast resulting in precip being primarily rain.
Further inland temps will stay colder and snow is expected for
these locations. On Sunday a weak shortwave will move in over
southwest Alaska from the west and bring light snow showers to
the area.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
The deepening low south of the eastern Aleutians will continue its
track north towards the islands with its front beginning to impact
the central to eastern Aleutians. The front will make it to the
Alaska Peninsula tonight and to southwest Alaska Friday morning.
Strong winds will be associated with this system with storm force
winds on the Pacific side of the Alaska Peninsula tonight into
Friday morning. The low will stall near the eastern Aleutians
Friday morning and then push off to the east Friday afternoon as
it begins to weaken. As the low exits into the Gulf Saturday
morning zonal flow will move in over the Bering with just some
weak showers lingering.

&&

.LONG TERM FORECAST (Days 4 through 7/Monday through Thursday)...
The extended forecast still looks to have high amplitude ridging
over mainland Alaska, with a low in the Bering Sea this weekend
into early next week. One difference from yesterday is that the
GFS is no longer attempting to push the low in the Bering through
the high pressure over mainland Alaska. It has come into alignment
with the other major models, so confidence is now high the
solution long term will be calm weather for southcentral Alaska
under high pressure, with active weather in the Aleutians due to
low pressure there. Gale force winds will be likely in the Bering
with this low.

Toward the end of the forecast period (Wednesday through Thursday),
there is another low that tracks through the Gulf of Alaska
underneath the high pressure system over mainland AK. There is
some uncertainty with the track of this low, with some models
favoring a southerly track in open water, while others keep it
closer to the coast. The more coastal track would bring some
active weather along the coast of Southcentral AK. Right now, due
to the overall pattern, the southerly track looks more likely.
However, this does bear watching next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Storm Warning 150 155. Gale Warning 120 130 131 132 136
137 138 139 160 165 170 171 172 173 174 179 180.

&&

SYNOPSIS AND MODEL DISCUSSION...KO/EZ
SOUTHCENTRAL ALASKA...JA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
LONG TERM...BJB