Small Craft Advisory 619, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
544 AM AKDT Mon Aug 17 2020

Corrected Southwest Alaska and Bering Sea/Aleutians discussion

.ANALYSIS AND UPPER LEVELS...

The ridge that has been sitting from the Eastern Bering to most
of the AK mainland for the past few days is now taking on more of
an omega/blocking formation with closed and stacked circulations
socketed in place both upstream over the Bering Sea and downstream
in the AK Gulf. The ridge axis has remained far enough west to
prolong the clear and warm spell for most of the mainland, and
much of the Mat-Su valley and Bristol Bay inland areas handily
breached 70F once again Sunday afternoon. The occluded front
extending from the Bering low has stalled from near St Matthew
Island to Unalaska and weakened with plenty of low cloud coverage
continuing over the Aleutians just south of the Bering low.

Winds this morning have become much lighter and variable across
most of the region as the Gulf low has pulled away from the coast
and allowed the NW-SE pressure gradient to collapse. Warm valley
conditions are fading a bit faster than the previous couple
nights with the lack of any northerly flow at the lowest levels
letting radiational cooling have a stronger influence on the
surface layer conditions. Most inland areas remain nearly cloud
free, but dense marine fog over the Kuskokwim Bay & Bristol Bay is
managing to creep up and develop near the coastline. Otherwise,
the streak of warm, dry and fair inland weather continues for the
time being.

&&

.MODEL DISCUSSION...

There are no new surprises on this forecast package. In the next
two days, the synoptic models show superb performance except when
handling the emerging circulation beneath the frontal boundary
over the North Pacific tonight. This is not a new issue, however,
latest solutions have shifted this next circulation farther
southeast of Kodiak before the ECM and GFS finds a common ground
as early as Thursday night.

&&

.AVIATION...
PANC...The models suggest Turnagain winds to increase tonight,
which will upped winds near PANC to at least 10 to 15 mph with
gusts near 20 to 25 mph. Winds will gradually diminish to 10 mph
by early Tuesday morning. The potential for showers near PANC is
feasible, but VFR conditions will prevail through the period.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (through Tuesday)...

The trend over the next couple of days will be toward cooler
temperatures, higher RH values, and increased chances of showers.
That said, temperatures will still peak into the 70s inland today
before a downturn on Tuesday. A weak easterly waves moves slowly
west across Southcentral tonight and Tuesday bringing increased
chances of showers and cooler temperatures. Stability indices
will likely support isolated wet thunderstorms over the western
Copper River Basin on Tuesday afternoon and evening. Broad
offshore flow with locally gusty gap winds have diminished with
the trend now toward coastal seabreezes. As the coastal ridge
builds this evening expect a brief period of gusty east-southeast
winds across Turnagain Arm, Knik River winds, and and southerly
winds along the Copper River. These winds should diminish
overnight tonight. The Turnagain Arm wind is expected to bend into
South and West Anchorage this evening before diminishing.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...

Portions of the Yukon-Kuskokwim Delta to the AKPEN have fog this
morning and the expectation is that it will mix out later this
morning. A couple of spots may hold onto it longer. The upper
level ridge is in place and will continue to influence the
weather across Southwest Alaska for today. Expect more dry and
warm weather. As time elapses, an upper level disturbance will
move westward across the southern Alaska and northern Aleutian
ranges which will enable showers to develop over the Kuskokwim
Mountains, northern Bristol Bay, and the Middle Kuskokwim Valley
on Tuesday. Because the ridge has been in place for awhile, the
antecedent airmass is parched and it may take a little longer for
the atmospheric column to become saturated than the models are
suggesting. The timing on Tuesday may be adjusted and some
locations may just get a trace of precipitation.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...

There is a 995 mb surface low in the Western Bering. This low is
slowly going to push eastward but it is weakening. This system
will continue to bring small craft winds and light showers to
portions of the Bering Sea. There will definitely be showers along
the chain. By the middle of the week, an upper level ridge will
build into the region. However, the ridge will bring the usual
low stratus/patchy fog.

&&

.MARINE (Days 3 through 5/Wednesday through Friday)...
The only feature of interest is a low tracking through the
eastern Gulf Thu through Fri. The current forecast indicates
sub-small craft winds. However, some model solutions suggest the
chance for small craft winds (or even low ends gale force winds)
may clip the offshore areas Thursday night into Friday.

&&

.LONG TERM FORECAST (Days 4 through 7/Thursday through Sunday)...

Looking ahead to later this week, models have been consistent
with two main features over the area. The first is an upper level
ridge in place over the Bering and the second is an upper level
low over the Gulf. By Friday, a Kamchatka low forces the ridge
eastward toward the Mainland, creating a more amplified pattern
for the weekend. As the ridge builds in Friday afternoon bringing
fair conditions to Southcentral, the Kamchatka low upstream will
drive a front across the Bering Saturday, bringing rain and
southerly flow to southwest Alaska. As the associated upper level
trough pushes eastward, increasing cloud cover and chances for
rain will arrive to Southcentral late Sunday.

&&

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

&&

SYNOPSIS AND MODEL DISCUSSION...AS/CB
SOUTHCENTRAL ALASKA...BC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PS
MARINE/LONG TERM...KO