Gale Warning 611, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
500 PM AKST Sat Nov 21 2020

.ANALYSIS AND UPPER LEVELS...

Satellite shows low pressure just south of St Matthew Island with
a front extending into Southwest Alaska. Another low is  near the
Barren Islands and is weakening as it moves up Cook Inlet.

Radar imagery shows rain and snow bands moving northwestward
across the Kenai Peninsula and Prince William Sound with a few
stray bands of rain/snow moving across southern Cook Inlet. Radar
imagery also shows showers moving across Bristol Bay with snow
farther north near Iliamna. And some rain and snow showers across
the Kuskokwim Delta region. Temperatures are in the lower to mid
30s across Southwest Alaska but colder in the teens and twenties
as you head inland across the lower Kuskokwim valley. From Kodiak
Island to Homer area temperatures are in the upper 30s with some
areas of light rain reported, farther north lower to mid 30s
across Seward and Kenai up to Portage and Whittier with rain and
snow reported across this area. While the Anchorage and MAT-SU
valleys are in the mid 20s to near 30. Much colder in the Copper
River Basin where single digits to below zero are reported. Gusty
winds across the MAT valley and decent down inlet flow from the
north and northeast from Anchorage to Kenai.

&&

.MODEL DISCUSSION...

Models are in better agreement through Monday, and confidence is
increasing as the details begin to emerge. The biggest issue are
models are starting to pickup on possible Hurricane force winds in
the southwest quadrant of the low tracking across the Gulf on
Monday, for now we went with high end storms, but this will need
to be monitored closely.

&&

.AVIATION...
PANC...VFR conditions becoming MVFR with light snow near or after
midnight. Winds will become southeast this afternoon and increase
with gusts up to 20 knots as the front moves across the area
tonight. Some light snow accumulations are possible overnight
through the morning hours. Expect VFR conditions to return by
mid- day on Sunday.

&&

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

Rain/snow showers near the coast will taper off through the
evening as a low moves over Cook Inlet. Brief snow showers are
possible across Anchorage and the Matanuska Valley early Sunday
morning as this low weakens. Mostly cloudy skies and high
temperatures near freezing are expected Sunday. Snow showers will
remain possible near higher terrain.

A deep low and its associated front will track into the western
Gulf late Sunday evening. Strong easterly winds and periods of
heavy rain are expected in Kodiak City through Monday morning.
Snow may potentially mix with rain in the associated northerly
winds on the backside of the low. However, given both relatively
warm air and sea surface temperatures, any accumulation would be
minimal. As the front quickly approaches the coast early Monday
morning, snow is expected across much of the southern Kenai
Peninsula and western Prince William Sound. Minimal accumulations
are likely before precipitation changes to a mix or all rain
through the day Monday. One notable exception will be Turnagain
Pass where all snow is expected and gusty easterly winds may
reduce visibility during the early morning hours. The low will
weaken and depart to the east by Tuesday, yielding more benign
conditions as a ridge builds in its wake.

&&

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

Weather is quiet save for some lingering cloud cover and showers
present from a decaying lower pressure to the southeast near
Homer, AK. This will change for the AKPEN and Bristol Bay tomorrow
evening. The low pressure system we have been forecasting is now
skirting the south side of the Aleutians and will arrive on the
south side of the AKPEN tomorrow night. Our model guidance for
this low has come into better agreement today, so we have
increasing confidence in the forecast for this system. We are
expecting 2-4 inches of snow for Bristol Bay and gusty winds with
this system. Temperatures should remain warm enough to keep snow
wet and heavy enough from being blow around. Gusty winds on the
backside of the low will produce storm force gusts through passes
on the AKPEN. This system exits late Monday and Tuesday looks
quiet for Southwest AK.

&&

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

The Bering Sea and Aleutians are quiet to start this evening's
forecast, with just some westerly flow and cold air associate
cumulus clouds. This however will soon change with two lows moving
into the Bering over the next few days. The first low is now
visible on satellite moving towards the Aleutians. This low will
move northeast and impact the Eastern Aleutians tomorrow night,
bringing rain, snow and gusty northerly winds behind it.

The second system is a low moving into the Bering from Kamchatka
on Monday morning. It's front will be strong enough to have storm
force winds as it enters the Western Bering. It will weaken as it
moves across the Bering through Tuesday, but will stay strong
enough to maintain storm winds until it reaches the Central
Aleutians. These winds will be southerly, meaning strong warm
advection will be in place ahead of the front, which will warm
temperatures and shift precipitation to rain for the Bering.

&&

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

Gulf of Alaska:

Good confidence with overall pattern but some uncertainty remains
in the details during the 3-5 day timeframe. Gales decrease to
small crafts by Tuesday afternoon as the low departs into the
southeastern Gulf and high pressure briefly moves over the area.
the next front enters the Gulf Wednesday with Gales likely. A low may
form along this front Wednesday near the Shelikof Strait but low
confidence on the timing and track of this low. This front will
weaken Thursday morning as it moves inland.

Bering Sea:

Fairly good confidence as a front with high end Gales moves across
the central and eastern Bering Tuesday. This front weakens as it moves
into Southwest Alaska Wednesday morning. Late Tuesday a low may
develop along the front near the eastern Aleutians and move into
the eastern Bering or Bristol Bay region. However low confidence
in track and strength as models are all over the place. Another
low with at least Gales will move towards the western Aleutians by
Thursday afternoon, but lower confidence with strength and track
of this low. It is certain that an active pattern will continue
through Thursday across the Bering.

&&

.LONG TERM FORECAST (Days 4 through 7...Wednesday through
Saturday)...

A highly amplified pattern to start the period will transition to
a more zonal like pattern across the Bering and Gulf by Thursday
morning with a series of lows/fronts riding west to east along
the upper level jet near the Aleutians and tracking into Southwest
and Southcentral with increasing chances of snow through the
period.

Wednesday a strong front extending from Southwest Alaska and into
the Gulf will move into Southcentral late Wednesday into Thursday
and weaken. This front will produce a large area of rain and snow
for Southcentral. A triple point low may form along the front
near Shelikof Straight and track into Cook Inlet late Wednesday,
however some uncertainty with track and strength of this low. A
weaker low is expected to move across the Gulf Thursday and Friday
with minimal impacts. Another strong low pressure system will
moves into the Bering and Aleutians with an accompanying front
moving south of the Aleutians and into the Gulf on late Friday
into Saturday. However lots of uncertainty on track of this
system. It does look certain that an active pattern will continue
through Saturday for much of the forecast area.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 119 136 137 139 140 150 160-172 174 177 178 180
		 STORM 120 130-132 138 155
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHCENTRAL ALASKA...AP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BB
MARINE/LONG TERM...RC