Small Craft Advisory 753, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
815 AM AKDT Sat Oct 3 2020

.ANALYSIS AND UPPER LEVELS...

Similar pattern, once again, remains in place this morning with
the ridge over western North America (slowly weakening) and a
broad trough across the North Pacific. There are signs that the
pattern is beginning to shift, however, as water vapor imagery
shows the flow across the North Pacific more west to east (zonal).
For the past week or so, the pattern has been very amplified or
meridional and now things are beginning to change. The current low
that affected the region today continues to move northwestward
towards Norton Sound. Another front is currently lifting northward
through Southcentral this morning in association with the low
over the Yukon-Kuskokwim Delta. As a result, gusty southeasterly
Turnagain Arm winds are blowing across west Anchorage, especially
near the airport, as well as the Anchorage Hillside. Palmer is
also reporting gusty southeasterly winds out of the Knik River
Valley now that the front has lifted through. Rain showers
continue to occur throughout the southern Mainland, as shown on
current radar imagery, with the typical locations on the leeward
side of the mountains being downsloped and other locations
receiving upslope.

The Bering Sea and the Aleutian Chain remain in a relatively quiet
pattern this morning as the jet stream remains well south of the
region. Therefore, the storm track is kept east of the region. The
cold air aloft has basically all been eradicated now with mostly
stratiform cloud cover with some breaks across much of the Bering
Sea and the Aleutian Chain. Multiple upper level shortwaves
moving around the backside of the current low over the Y-K Delta
are keeping occasional showers over the Bering. Therefore, these
will be more lift driven rather than the unstable case yesterday
when cold air was flowing over the Bering and picking up
moisture.

&&

.MODEL DISCUSSION...

Model guidance generally remains in good agreement on the synoptic
scale features out through 3 days. The next storm system is coming
into better agreement on the latest model runs this morning with
the typical subtle differences between models on the exact track
and exact intensity. For the most part, though, there is much
agreement as compared to previous days and we now have higher
confidence in the forecast. The EC remains the furthest east with
the storm track this morning while all the other models (GFS, NAM,
and Canadian NH) are almost in lockstep with each other.

&&

.AVIATION...
PANC...VFR conditions will persist. Gusty southeast winds will
persist through this evening before diminishing. Some rain showers
are possible this morning that may result in a cloud deck of
5000ft, therefore, only hinted at this but didn't make it a solid
cloud deck. As the next system approaches, expect a wind shift to
out of the north for Sunday morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Monday)...

The strong low dominating the Gulf over the last couple days
has weakened significantly, exited the Southcentral area, and
is slowly making its way across the Southwest today. Multiple
embedded shortwaves are rotating around the now broad upper low,
keeping rainfall along the Southcentral coast today and tonight.
As a result, the threat of flooding for the Seward area and Kenai
River near Cooper Landing will continue.

By Sunday morning, another deep low enters the southern Gulf.
Models have been struggling with the path of this system over
the last couple days, but have since come into better agreement,
placing it just east of Kodiak Island today. This is an ideal
setup for strong winds over the western Gulf and southern Cook
Inlet, including widespread gales and a period of storm force
winds on Sunday. Thus, synoptic winds were increased from the
previous forecast - with emphasis over the Gulf and coastal
waters. The majority of the impacts associated with this low
will be marine related, specifically with regard to winds.
However, the coastal regions will see heavy rainfall by Sunday
afternoon, diminishing to light rain by mid-morning on Monday.

Downsloping will not be an issue with this low, as the more
easterly track will produce a more northerly/northeasterly low
level flow over Southcentral on the north side of the low. Thus,
those areas which have been dry with the current storm will
likely see some periods of light rain on Sunday. There remains,
however, some uncertainty with the path of this low. Should this
system track further east (as at least one model shows), winds
along southern Cook Inlet and the western Gulf may end up weaker
than currently forecast. Additionally, with a more easterly track,
Anchorage and the Mat-Su Valley would remain dry.

&&

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

A broad low moving northward is bringing widespread showers to
much of Southwest Alaska. Highest totals are expected around
Bristol Bay in southwest flow as the low departs, though amounts
will remain minimal. Showers will taper off midday Saturday as
slightly drier air builds in, however slight precipitation
chances will persist under a series of upper level shortwaves.
Temperatures will gradually fall through early next week.

&&

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

Showers will persist through the weekend in a general northerly
flow. High pressure will build over the western Aleutians Sunday
into Monday leading to calm conditions. Gusty winds out of bays
and passes may occur Sunday between Unalaska and Adak between
relatively strong high and low pressure.

&&

.MARINE (Days 3 through 5/Monday through Wednesday)...

Bering/Aleutians

Light northerly flow continues across the central/eastern
Bering/Aleutians on Monday. Winds flip to southerly and increase
to small craft levels for the western Aleutians late Monday due to
an approaching Kamchatka low. Early Tuesday, southeasterly flow
ramps up to gale force across the western Bering/Aleutians along
with widespread rainfall. This wind/rain spreads into the central
Bering/Aleutians by mid to late Tuesday. Early Wednesday, the
Kamchatka low migrates towards the western Bering, with westerly
small craft/low end gale force winds expected across the western
and central portions of the Bering/Aleutians, while eastern areas
see southerly winds pick up to near gale force along with
plentiful rain. By late Wednesday the low in the western Bering
weakens with winds transitioning to westerly and falling back to
small craft levels.

Gulf of Alaska

On Monday, a weakening low will be parked over Prince William
Sound early, with this storm system quickly heading interior and
diminishing by late Monday. As a result, southwesterly gale force
winds early on Monday, across the Gulf, should diminish below
small craft advisory levels by the afternoon/evening hours.
Generally light westerly flow then takes over for Tuesday and
Wednesday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The extended forecast pattern remains progressive through the
work week. The next storm to impact the Gulf of Alaska will lift
from the Pacific into Sunday/Monday. This will again bring
unsettled weather to Kodiak, but will mainly spare much of
Mainland Alaska. The forecast track continues to shift east,
sparing much of Prince William Sound and Seward from the past week
of rains. A barrier jet is likely to impact the coast during that
time, as winds turn offshore by Monday. Across the Bering, a
transient ridge will slide east through Wednesday. The next Bering
low will slide across the Kamchatka Peninsula and move SE towards
Bristol Bay by Friday. This storm track leaves a very low
potential for coastal issues through this time.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm Warning 119 130 139
Gale Warning 120 131 132 138
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MV
SOUTHCENTRAL ALASKA...KM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CJ
MARINE/LONG TERM...SS/BG