Small Craft Advisory 865, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
401 PM AKST Thu Nov 12 2020

.ANALYSIS AND UPPER LEVELS...
A broad upper low is over Southcentral/Eastern Bristol Bay and is
moving eastward. Bands of snow and rain showers, associated with
this feature, extend from Bristol Bay to across much of
Southcentral and the Gulf of Alaska. Instability showers with cold
advection on the backside of the low center are evident by the
presence of open cell cumulus extending from the Eastern Bering
Sea, across the AK Pen, to south of the Gulf of Alaska. Strong
west to northwest winds is also present in these areas.

&&

.MODEL DISCUSSION (short term through day 3)...
Models are in generally good agreement and reasonable through the
short term over Southcentral. The main concern will be outflow
wind conditions, so will be leaning toward higher resolution
models and hand edits.

Out west, models diverge significantly on the positioning of a
strong low heading toward the Western Aleutians Sunday. However,
all of the available models are pointing toward at least southerly
gales over the Western Aleutians/West Bering Sea Saturday night
into Sunday.

&&

.AVIATION...
PANC...MVFR/IFR ceilings and visibilities with areas of fog and
low stratus are expected through early tonight with some
potential improvement to mainly MVFR conditions Friday. Light
winds will prevail.

&&

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

A broad low in the Gulf is leading to light rain showers near the
Copper River Delta through this evening, with flurries persisting
across Southcentral and the Kenai Peninsula. These showers will
gradually taper off overnight. A pattern change is expected into
the weekend, and relatively higher pressure developing to the
north combined with the aforementioned Gulf low will lead to
northerly flow. This will bring a clear, dry pattern to much of
the region. Gusty winds will develop through mountain gaps,
especially towards the end of the weekend. However, given the
lack of upper level forcing, these are not expected to be overly
significant.

&&

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

A broad upper level trough travels south across the Bering Sea
and the Southwest through Saturday morning. Light snow showers
are expected across the most of the mainland, with the heaviest
amounts confined to the higher elevations, particularly as the
trough passes through. The Kuskokwim Valley may see less than an
inch of snow accumulation through tonight, and anywhere from 1-3
inches in the mountains. Additionally, this front will bring
northerly flow and much colder air so expect a drop in
temperatures over the next few days. Drier conditions should
arrive Saturday evening ahead of a ridge tracking east across the
Bering. Northerly flow will persist across the Southwest mainland
ahead of the ridge through Sunday.

&&

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

Primarily westerly flow expected through tonight as a broad upper
level trough makes its way south towards the Aleutian Chain. By
Saturday morning, the trough exits to the North Pacific and flow
behind it transitions to northerly. At the same time, ridging
forms out in the Western Aleutians and quickly pushes east, thus,
flow will remain northerly ahead of this ridge through Sunday.
Expect significant cold air advection to accompany this. A low
approaches the Western Aleutians Sunday evening. Models are in
disagreement on the low center, which will determine if storm
force winds will be a factor. So far, models keep storms to the
south and just skim the Central Aleutian coasts. This setup will
continue to be monitored over the next couple days.

&&

.MARINE (Days 3 through 5: Sunday through Tuesday)...

Gulf of Alaska:

Gusty northwesterly gale force winds over Kamishak Bay and the
Barren Islands will continue through the day Sunday before
tapering off Monday morning. Small craft winds will linger during
the day Tuesday across the Gulf waters before a low begins to
retrograde westward across the northern Gulf. There is low
confidence with this system, but gusty northerly flow is looking
increasingly likely across the northern Gulf waters beginning
Tuesday afternoon.

Bering Sea:

There is increasing confidence that a storm force low will enter
the western Bering Sunday morning, forcing a ridge eastward. Gale
force northerly winds over the eastern Bering will last through
Sunday before diminishing Sunday night. The low will track
eastward, spreading storm force winds across the Bering waters
through Monday. There is increasing confidence gale force winds
will persist across the Bering waters through Tuesday as this
broad complex low gradually lifts northward.

&&

.LONG TERM FORECAST (Days 4 through 7: Monday through
Thursday)...

The long terms starts with a large, amplified upper level ridge
in place over the eastern Bering and extending over the western
mainland. Upstream, a well developed surface low over the central
Aleutians will bring warm southerly flow and rain to the Aleutian
Chain Monday into Tuesday. By Tuesday morning, a strong upper
level low originating from over Siberia quickly pushes eastward
and phases with the remnant upper level energy from the Aleutian
low. By Tuesday night, a broad complex low will be in place across
the Bering Sea with an ample supply of cold air filling in on the
backside. Upper level shortwaves embedded within this low will
eject eastward across the southern mainland beginning Wednesday
night. Although model solutions show great timing discrepancies,
this pattern sets the stage for an active weather pattern ahead
with the potential for development of several areas of low
pressure.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning: 351,352,130,131,132,138,150,155,160.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BC
SOUTHCENTRAL ALASKA...AP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KM
MARINE/LONG TERM...KO

SPECIAL WEATHER STATEMENT...CORRECTED
National Weather Service ANCHORAGE AK
259 AM AKST Fri Nov 13 2020

AKZ145-150100-
Susitna Valley-
Including the cities of Talkeetna, Willow, and Cantwell
259 AM AKST Fri Nov 13 2020

There is a freeze up ice jam on the Talkeetna River which is
currently causing flooding of two residences in East Talkeetna
along Mercedes Drive. Be alert for changing conditions as water
levels will fluctuate as the ice jam shifts.

In the event that flooding becomes worse, notify the Talkeetna
Fire Chief and/or the Matsu Borough.