Small Craft Advisory 643, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
548 PM AKDT Thu Sep 5 2019

.ANALYSIS AND UPPER LEVELS...
The upper level low center is now north of the Bering Strait and
extends south over the Alaska Peninsula and then far to the
southwest in the Pacific (to near 30N 170E). This is a very long
tap of moisture and can be seen well on IR satellite. Southwest
Alaska is under this moisture with Southcentral under the upper
level ridge. The jet stream at 250 mb is just to the south of the
eastern Aleutians and will be the focus for the development of
the next low to move into the region.

&&

.MODEL DISCUSSION...
Models are in good agreement and doing better overall than
yesterday. The feature from yesterday that they were struggling
with the most was the low that will develop along the front south
of the Alaska Peninsula Friday and models have all come into a
common solution with it. This solution does bring the low farther
east with a stronger pressure gradient over the southwest Alaska
so that has been accounted for in the new forecast packages.

&&

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

&&

.FIRE WEATHER...
The biggest fire weather concern will be for conditions in the
Copper River Basin, and specifically near the Tokaina fire, on
Saturday. The ridge will be near the AlCan border and bringing in
areas with temperatures approaching 70 and RH values under 30
percent. South to southeast winds will also blow through channeled
terrain in the Chugach Mountains and along the Copper River.

The Swan Lake fire is beginning to produce more smoke again
today(seen on visible satellite) under the sunny skies. The sunny
skies should be around through tomorrow before cloudier condition
return on Saturday.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3;
Tonight through Sunday evening)...

An upper ridge and associated high pressure will bring mostly
dry conditions across Southcentral through Saturday. Highs near 70
are possible over interior valleys. Farther west, a front will
gradually track over Kodiak Island Saturday morning bringing
moderate rain for much of the day. Gusty southeasterly winds are
likely west of the Barren Islands as well. The front is expected
to weaken as it moves to the east, although rain is likely for
the Kenai Peninsula coast early Sunday morning in persistent
southeasterly flow. A brief period of rain remains possible for
the Anchorage area Sunday morning as well given decent upper
level support, though will not last beyond midday as drier air
builds in from the west.

&&.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3/Tonight
through Sunday)...
Wet and windy weather is the big weather story for the next couple
days, particularly along the Southwest Alaska coast. A series of
lows will track northward along a frontal zone currently oriented
north to south across the eastern Bering Sea and southern Alaska
Peninsula. These will be supported aloft by an amplifying trough
and strengthening southerly jet. As these features move up the
front, the front will be pushed farther and farther to the east
and into Southwest Alaska.

For tonight into Friday, the bulk of rain and strongest winds
will be from the southern Alaska Peninsula (south of Port Heiden)
northward to the western portion of the Bristol Bay area (from
around Dillingham westward) and on up across the Kuskokwim Delta.
The wind and rain will then spread north and eastward across the
remainder of Southwest Alaska Friday afternoon through Saturday.

The latest model guidance has trended notably stronger with the
low moving up the front Friday afternoon through Friday night.
This will really intensify winds just east of the low track. Have
strengthened winds considerably in the latest forecast. While
there is some uncertainty in the low track, it appears the
strongest winds will occur Friday afternoon through Friday night
along the Alaska Peninsula from east of Cold Bay all the way up
to the vicinity of King Salmon and Naknek. Bristol Bay itself will
also see some of the strongest winds.

Strong pressure rises on the back side of the low will lead to a
quick shot of south to southwest winds along the Alaska Peninsula
Friday night and across Southwest Alaska on Saturday. Rain and
winds will then diminish Saturday night as the low exits to the
north. Another weaker storm system will enter the eastern bering
Sea on Sunday, with showers approaching the Southwest coast.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through
3/Tonight through Sunday)...
The weak low along the Aleutians today will exit to the eastern
Bering Sea on friday as a new system arrives in the western
Aleutians. This storm will track eastward along the Aleutian
Chain, reaching the eastern Aleutians Sunday as the next storm in
line arrives along the western Aleutians. None of these systems
look very strong - just your typical small craft to perhaps some
small areas of gale winds as they move through.

&&

.MARINE (Days 3 through 5)...

Beginning the extended marine forecast period on Sunday,
conditions will be easing across all of the marine areas. Over the
Gulf of Alaska, a ridge will be moving east and weak SE winds will
be prominent through Tuesday. West across the Bering, multiple
areas of low pressure will weaken, giving way to light northerly
flow west of 180. Closer to SW AK, winds around a decaying low
will be southwesterly generally south of the AKPEN. These winds
should remain at small craft levels or lower, while winds in
Bristol Bay and along the western coast will be southerly and
remain sub gale through Tuesday.

&&

.LONG TERM FORECAST (Days 4 through 7)...

Beginning the extended period forecast on Sunday evening, high
pressure will keep benign weather locked in east of the Chugach
and Talkeetna mountains. Areas from Kodiak through the coastal
areas of Prince William Sound will see some showers come to a
close on Sunday as weak ridging builds from the south. The next
front will bring showers to all of the coast from Monday evening
on. Across the western coast, cooler and wetter conditions will
remain a mainstay well into next week. A transient ridge is
expected to build across the western Aleutians through the middle
of the week as long term solutions are pointing towards a strong
storm moving into the western Bering around Thursday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gales 150 155 160 165 180.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...AP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...SEB