Small Craft Advisory 604, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
500 AM AKDT Sun Aug 9 2020

.ANALYSIS AND UPPER LEVELS...

There is a broad upper trough over much of the state of Alaska,
the Bering and over NE Russia. There are several organized and
weak lows embedded in the longwave trough. The most organized one
being the low in the Gulf Of Alaska. There is a jet core pushing
over Adak and a more potent jet core bisecting the Gulf Of Alaska
and SE AK. "Water Vapor" satellite imagery shows distinct dry air
intrusion over the southern Gulf Of Alaska to the North Pacific on
the back side of the frontal boundary. Also noteworthy, smoke
from the Siberian fires has moved into the Bering and is visible
on satellite imagery.

&&

.MODEL DISCUSSION...

For initialization purposes, compared several ASCAT (advanced
scatterometer) passes to winds projected by the models and both
the GFS and NAM did well pinging into the gales in portions of the
Gulf Of Alaska. The global models and the NAM retain decent
consensus wit the placement of the synoptic features the next 48
hours over the GOA, North Pacific and Bering.

&&

.AVIATION...
PANC...Overnight the ceiling fell below 5000 ft at both PANC and
PAMR. As of 11:53z the cig at PANC was at 5000 feet. The Kenai
radar (PAHG) was active overnight with showers over portions of
Cook Inlet and Turnagain Arm. Light rain will fall over the
aerodrome this TAF period. The models are suggesting light winds
for PANC until 00z Monday when westerly flow sets up.

&&

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

A strong low in the Gulf of Alaska is bringing gale-to-storm force
winds to the marine areas this morning and rainfall across the
north Gulf coast. The low is moving eastward quickly and will be
out of the area by this evening. While the surface low will
have weakened and moved inland by overnight tonight, the upper
level low will remain near the Alcan border which will keep a bit
of moisture around the Copper River Basin. This upper level low
will also leave some instability over Southcentral that will keep
some lingering showers around. As was the case yesterday, the
most unstable air will be over the Susitna Valley as there will be
enough breaks in the clouds to keep the potential for a few
afternoon and evening thunderstorms.

A new upper level low will dig into Southwest Alaska Monday and
then into Southcentral for Monday night into Tuesday. This will
bring some more showers into the region; especially from the
Kenai, Chugach, and Talkeetna Mountains eastward.

&&

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

Expecting a showery day today along coastal areas of Southwest and
the mountains of the AKPEN. An upper level trough is positioned
over the eastern Bering Sunday morning and is expected to move
inland throughout the day Sunday. Rainfall is primarily along the
system's cold front, which is not expected to push far inland due
to wind shear from a low over the Gulf of AK. As a result rain
should taper off after the front crosses the Kilbuck Mountains and
into the Middle Kuskokwim Valley. On Monday, a more impressive
trough will dig south from the Bering Strait, which should bring
another round of rain to the region. With greater upper level
support, rain is expected to be more widespread than on Sunday. By
Tuesday, flow aloft will transition to the northeast, which will
help to bring in a drier, warmer airmass from the interior.

&&

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

The main weather story for the Bering Sea and Aleutian Chain is
an upper level low moving east towards Shemya Sunday morning. It's
front is currently bringing small craft winds and rain to the
western Aleutian chain. This front will move east through the
forecast period, arriving over Dutch Harbor Monday evening. Recent
model guidance indicates a triple point low forming along the
front to the south of Dutch Harbor around this time. This should
lead to some heavier rain as it moves over the eastern Aleutians
Monday night and into Tuesday morning. Otherwise, the parent low
should slowly occlude over the western Aleutians through Tuesday
as it loses upper level support. This will bring low stratus and
light rain to most of the region to the south of Saint Matthew
Island, where shortwave ridging will keep winds on the lighter
side and devoid of rain through Tuesday.

&&

.MARINE (Days 3 through 5: Tue through Thu)...

Low pressure over the Gulf Tuesday afternoon weakens through the
evening hours. Looking to the west, models are in good agreement
with a low positioned northwest of Adak Tuesday afternoon. The
associated front, bringing widespread showers and small craft
advisory winds, will continue to push into the Southwest coast by
late Tuesday as the system slides eastward and weakens through
Thursday morning. Model confidence decreases Wednesday afternoon
as some models try to develop a weak low south of Kodiak Island,
which would continue into the Gulf through Thursday. However,
models agree that winds should remain below gale force throughout
the forecast period.

&&

.LONG TERM FORECAST (Days 3 through 7: Wed through Sat)...

A front moving in over Southwest Alaska on Wednesday afternoon
associated with a weakening low in the Bering will bring a chance
of rain showers to the region. However, models are struggling with
the position of the associated low and whether it will keep a
track farther south, which would keep a drier solution for the
Southwest coast with the majority of the precipitation over the
Alaska Peninsula. Meanwhile, over Southcentral Alaska, models are
hinting at an upper level wave moving into the region, which will
keep a widespread chance of showers in the forecast through
Thursday with this system. A low trying to develop over the Gulf
will bring the next chance of showers to the North Gulf Coast for
the end of the week into the beginning of the weekend. There is
still model uncertainty as to how far north this low and
associated front will move.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm 351. Gale 119 120 131.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CJ
MARINE/LONG TERM...ALH