Small Craft Advisory 196, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
410 PM AKST Thu Feb 27 2020

.ANALYSIS AND UPPER LEVELS...

An upper trough and associated surface low moving eastward over
the Gulf are still kicking off a few snow showers along the
eastern Gulf Coast. Generally fair skies were observed elsewhere
across Southcentral and across much of the southern Mainland.
Gusty outflow winds associated with the retreating low over the
Gulf were observed over the eastern Kenai Peninsula. A broad upper
through and weakening surface lows extended from west of Attu to
over the eastern Aleutians. Satellite imagery shows the early
stages of development of a surface low along a broad frontal
boundary over the western north Pacific.

&&

.MODEL DISCUSSION...
The most notable model difference occur Friday and Saturday with
the next low brewing over the western Pacific. This system
develops under a fairly strong upper jet and heads into the Bering
Sea later Friday. Center positioning of low is still in question,
but confidence at this point is moderate to high on gale to storm
force wind potential across the Aleutians and Bering Friday into
Saturday. Accumulating snow potential still looks reasonable for
Saturday and Saturday night from Bristol Bay to portions of
Southcentral.

&&

.AVIATION...
PANC...Generally VFR conditions are expected through this evening.
There is a possibility of IFR/LIFR ceiling and/or visibilities in
fog Friday morning. Light winds should prevail over the next 24
hrs.

&&

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

Clear and dry conditions will prevail across much of Southcentral
through the first half of Saturday as a ridge of high pressure
builds across the western half of the state. For the Copper River
Basin and Delta, scattered cloud cover and the threat for an
isolated to scattered snow shower will remain in the forecast
through early tomorrow morning as a weak shortwave dives across
the eastern half of Southcentral overnight. With the ridge
situated over the interior and a surface low lingering in the
eastern Gulf, gusty northerly outflow winds will persist along the
immediate coast. With mainly clear and dry conditions for most of
the region, temperatures overnight tonight and tomorrow night
will drop to near zero around Cook Inlet to well below zero across
the Susitna Valley, interior Kenai Peninsula, and Copper River
Basin. High temperatures the next two days will range from the
single digits in the Copper River Basin, to lower to mid 20s from
Cook Inlet north to the Susitna Valley, to lower to mid 30s for
Kodiak City.

A frontal system is slated to enter the western Gulf late Friday
night, first impacting Kodiak Island with a mix of rain and snow
and gusty southeasterly winds. This system will then move toward
the central and northern Gulf for Saturday with a new triple-
point surface low developing, bringing widespread snowfall across
Southcentral late Saturday through Sunday. As the low tracks
toward Prince William Sound, a brief period of southeasterly gap
winds will develop from Passage Canal through Turnagain Arm. Right
now snow amounts look light across Cook Inlet and The Mat-Su
Valleys through Sunday, with a general 3 to 6 inches expected and
some areas of blowing snow in gap locations and along the
immediate Cook Inlet coast.

There is still some uncertainty regarding timing and position of
the developing low late Saturday into Sunday. Any shift in the
track will affect winds and snow amounts, especially along Cook
Inlet and the Anchorage Bowl. Stay tuned for updates.

&&

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

Generally clear conditions and weak offshore flow are expected
across Southwest Alaska through early Saturday. The next impactful
weather event for Southwest will be an approaching front
associated with a deep Bering low. This front will arrive to the
coast by Saturday morning. Gusty southeasterly winds and snow are
expected along Bristol Bay coastal locations for Saturday. This
combination of wind and snow may cause reduced visibility at
times. By Saturday afternoon, precipitation types become a little
less certain along the Alaska Peninsula, however current thinking
is that temperatures will warm enough to change snow over to a
rain/snow mix, and likely all rain by Saturday evening, especially
over the southern Alaska Peninsula. By Sunday, conditions are
still expected to remain unsettled as colder northerly flow
returns, allowing any lingering precipitation to change back over
to snow, especially over the Kuskokwim Delta coast.

&&

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

An active weather pattern across the Bering is expected for the
end of the week. By Friday morning, a leading front associated
with a deepening, storm force low approaches the western
Aleutians. Gusty southeasterly winds and a rain/snow mix is
expected initially as this front moves in across the Aleutian
Chain Friday morning. As warmer southerly flow works its way in, a
change to all rain is expected during the first half of the day
Friday. A Winter Storm Watch remains in effect for Shemya and
Amchitka from Friday afternoon through Saturday afternoon, where
precipitation is expected to remain all snow at this time.

By Friday evening, southwesterly storm force winds will move in
over the Rat Islands as the low center gradually lifts northward
into the western Bering. While the low looks to remain nearly
stationary for Saturday, northerly flow on the backside of the low
will allow colder air to wrap around. This will keep gusty
northerly winds in place for the western Aleutians through most of
the weekend.

Meanwhile for the rest of the Bering, the leading edge of the
front progresses eastward. By Friday evening, southerly gale force
winds will reach the Pribilofs and central Aleutians, and by
Saturday morning, this now weakening front will reach the eastern
Bering. As this front moves eastward, precipitation is expected to
spread across the Chain with snow possible at the onset, however
a quick transition to rain/snow mix and then all rain is likely.

&&

.MARINE (Days 3 through 5 Sun through Tue)...
Gale force winds will continue around the low in the western
Bering on Sunday then diminish to small craft range Sunday night.
Gales are expected from south of the Alaska Peninsula through the
Gulf Sunday and Sunday night associated with a low in the northern
Gulf. Winds are expected to be near storm force in the offshore
waters of the Gulf Sunday evening.

&&

.LONG TERM FORECAST (Days 4 through 7 Mon through Thu)...
An upper level trough will dig into southern Alaska Monday and
Tuesday then slide east Wednesday and Thursday, with the axis near
the Canadian border Thursday afternoon. High pressure over
extreme northeast Russia on Monday will slide eastward behind this
trough, pushing into the western Bering on Tuesday and into
western Alaska by Thursday. The Ensemble means are in fairly good
agreement, but the deterministic models are all over the place on
the details. Therefore the forecast confidence past Tuesday is
rather low.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Storm Watch 191.
MARINE...Gale Warning 127 155 165 170 171 172 173 174 176 178 179
185 412 414.
Storm Warning 175 177 411 413.
Heavy Freezing Spray 129 130 412 414.
FIRE WEATHER...NONE.

&&

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