Heavy Freezing Spray Warning 200, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
652 AM AKST Tue Nov 30 2021

.ANALYSIS AND UPPER LEVELS...

An upper level low with its corresponding surface low are
currently spinning over the northwest Gulf of Alaska. As a result,
this system is bringing a great amount of "warmer" air northward
as it displaces the deep Arctic air that has been sitting over
much of Alaska to the west. This can be seen when looking at the
water vapor loop and nighttime microphysics which show the main
upper level low that has been sitting over interior Alaska these
past couple days over the Yukon-Kuskokwim Delta. To the west of
this, northwesterly flow continues throughout much of the Bering
as very cold air continues to flow over the relatively warm water
surface of the Bering causing occasional snow showers for the
Pribilofs, Dutch Harbor, Cold Bay, and King Cove. King Cove has
been observing sustained 35 to 50 mph west-northwesterly winds
most of the night with gusts upwards of 68 mph or (59kts). These
snow showers continue to lower visibility to between the 1 to 3
mile range though an occasional heavier snow shower is reducing
visibility to as low as three quarter mile.

Looking back at Southcentral, as the surface low continues
spinning over the Gulf, northeasterly winds have made it into the
Matanuska Valley with Palmer gusting as high as 36 mph so far and
Wasilla gusting upwards of 45 mph as a tight pressure gradient has
taken shape. As a result, temperatures are MUCH warmer compared
to last night at this time in the mid 20s. Anchorage Ted Stevens
International Airport has also warmer dramatically from last night
with a temperature of 25 degrees and a 10 kt north wind. The only
below zero temperatures able to be found across Southcentral this
morning is in the Copper River Basin with Gulkana sitting at 2
degrees below zero. Cordova is currently the warmest spot with a
temperature of 39 degrees! Therefore, any precipitation falling
there is rain this morning. Further west, Whittier has also warmed
to as much as 35 degrees earlier in the evening but has since
cooled back to just above freezing with light snow being observed.
Homer is also observing snow with warmer temperatures this
morning as the low is pushing moisture over the mountains to the
east. Kodiak is now on the backside of the system with gusty west-
northwesterly winds and temperatures back below freezing as
colder air advects into the area.

Looking across Southwest, the coldest air across the southern
Mainland is currently across the Kuskokwim Delta where
temperatures are in the single digits and teens below zero. This
combined with gusty northerly winds is resulting in wind chills to
as low as 40 below zero. As a result, A Wind Chill Advisory
remains in effect this morning. Temperatures are also this cold
for areas such as Aniak and Sleetmute though winds are light and
variable. Light snow is currently falling across Dillingham and
interior areas of Bristol Bay this morning with temperatures in
the single digits below zero and single digits above zero making
it dry and powdery. Lastly, a frontal system can be seen on
satellite moving into the western Bering/Aleutians in association
with a North Pacific low.

&&

.MODEL DISCUSSION...

Models continue to be in good agreement on the evolution of the
synoptic features out through Day 3. Yet again, continuing on
with the rinse and repeat as this has been the story for the last
several days now is the nitty gritty details of the smaller scale
features. The forecast challenge remains with the timing and
progression of individual shortwaves which continue to make for a
very tough forecast regarding sensible weather across
Southcentral, especially regarding the Anchorage Bowl, northern
Kenai Peninsula, and Mat-SU Valleys area. As this low continues
northward and inland, models are struggling with resolving exactly
how the low will interact with the surrounding mountains and
such. Therefore, this package was mostly spent in the above areas
to continue fine tuning what may happen.

Out west, models are in good agreement on the evolution of the
pattern with persistent northwesterly flow, storm force system
moving into the western Bering later today. Any edits this package
were continuing to fine tune the gusts through bays and passes
along the Alaska Peninsula and continuing to fine tune the PoPs,
QPF, Snow amount for the Bristol Bay area today. See Southwest
section for more details. Models also agree on a much stronger
storm force frontal system moving into the western Bering/Western
Aleutians Wednesday night through late in the week.

&&

.AVIATION...
PANC...VFR conditions are expected to continue through around 18z
this morning before lowering to around 5000ft. Ceilings are
expected to lower further into the MVFR range around 21z as well
as visibility lowering to around 2-3SM as light snow is expected
to move over the terminal at this time. Light snow is expected to
continue through the remainder of the TAF package peaking between
01/03-12z when ceiling and visibility may drop to IFR conditions.
Conditions are expected to gradually improve back to MVFR
conditions after 01/12z. Winds are expected to remain generally
10kts or less throughout the TAF package.

&&

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

A vertically stacked low over the northern Gulf will lift northward
across Southcentral this afternoon through tonight. An upper
level low and trough digging southeastward across the Alaska
Peninsula this morning will move into the western Gulf this
evening, then lift northward toward Southcentral. These features
will cause persistent precipitation along the Gulf coast, with
periods of mostly light snow inland. The snow forecast for inland
areas from Anchorage to the Mat-Su and the Copper River Basin is
particularly challenging. The upper low which moves inland first,
opens up into a fairly diffuse trough. There is then some
uncertainty in the track of the stronger short-wave which
approaches late tonight. This makes it difficult to nail down the
timing and accumulation of snowfall. Nonetheless, most areas
should see some light snow and accumulation will generally be
very light.

The current storm over the northern Gulf has brought warmer air
with it and temperatures have steadily risen across the region.
While this has led to a changeover to rain in Cordova, all other
areas remain cold enough for snow. This will be short-lived
however, as Arctic air accompanies the trough crossing the Alaska
Peninsula, moving into the Gulf this afternoon then northward
across Southcentral tonight into Wednesday. This will change all
precipitation back to snow. The primary impact of the cold air
advection will be another round of strong gap winds across the
western Gulf and Kodiak Island. As the surface low heads inland
later today, winds blowing from Bristol Bay into Kamishak Bay,
will bend northward into southern Cook Inlet and Kachemak Bay.
This will bring another round of blowing snow and reduced
visibilities from Homer northward to Anchor Point, where a
Winter Weather Advisory has been issued.

The upper level low which settles over the northern Gulf tonight
will exit eastward Wednesday night through Thursday, allowing even
colder air to filter southward through the Alaska Range into
Southcentral. Temperatures will trend downward once again, with
sub-zero temperatures likely as we head to the end of the week.
The one wild card in how cold it gets will be cloud cover, as it
does look like a short-wave trough will dig south across the
mainland Thursday through Thursday night. Depending on its track,
there could be some clouds out ahead of it which would slightly
moderate surface temperatures. Meanwhile, the deep cold air
combined with persistent pressure gradients will maintain gap
winds along the coast.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 2: Today
through Wednesday night)...

An upper level low situated over the Southwest coast is working in
tandem with a surface low in the Gulf to produce a band of light
snow draped across Southwest Alaska from just west of the
Kuskokwim Mountains to the southern Bristol Bay coast. This band
of precipitation is expected to continue to linger throughout the
day today. Snowfall associated with this band of precipitation is
expected to produce only slight accumulations, around 1 to 2
inches. Further bands of light snow associated with the Gulf low
may cross the Aleutian Range into eastern portions of the region
tonight through Wednesday, producing light accumulations for
Sparrevohn and Iliamna.

Cold northerly flow wrapping around the back side of the Gulf low
is currently keeping temperatures in the negative teens across
western portions of the Kuskokwim Delta region. Combined with
winds, this is producing wind chills near negative 40 which are
expected to continue through the day today before the pressure
gradient driving the winds begins to relax as the Gulf low pushes
further east. Cold northerly flow, however, will continue to push
across Southwest Alaska, shutting off the moisture stream and
resulting in lowering temperatures area-wide over the next
several days.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 2:
Today through Wednesday night)...

Blowing snow and gap winds will be the main impacts for the
eastern Aleutians and AKPEN through Thursday. Cold air wrapping
around the back side of a broad low in the Gulf will enhance snow
showers and gusty northwesterly winds across the eastern Bering
Sea. These conditions will combine to produce blowing snow
with visibilities dropping to as low as one half mile at times,
particularly along the Alaska Peninsula as far northeast as Port
Heiden through this evening. See the Winter Weather Advisory for
the Alaska Peninsula for more details.

As the low shifts eastward into the Gulf, the strongest cold air
advection will follow, resulting in intensifying gap winds
through the AKPEN beginning today. These winds, enhanced by a strong
upper-level shortwave will produce widespread gale force winds
with storm force gusts possible out of gaps along the AKPEN
through Wednesday night.

Out west, conditions will be dominated by a storm-force low
crossing the western and central Bering. This low is expected to
produce widespread gales and snow showers through the western and
central Aleutians through Wednesday night.

&&

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

Gulf of Alaska: There is high confidence a low pressure system
will linger in the Gulf while slowly weakening. Gale to storm
force winds are likely through the Barren Islands on Thursday.
Winds should subside below gale force on Friday.

Bering Sea/Southwest: There is high confidence a gale to storm
force front will move into the western Bering on Thursday,
extending east off of a deep Kamchatka low. The front is expected
to weaken below gale force once it reaches the Pribilof Islands,
but westerly gales are likely to develop behind the front. By
Saturday, confidence is moderate that another gale force front
will move into the Western Bering, but exact details where the low
center is expected remains low.

&&

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

Forecast confidence of a high amplitude, progressive pattern is
high through the extended period. Starting Thursday a low over
the Kamchatka Peninsula will pull a deep fetch of warm air and
moisture across the Bering Sea. The parent low is expected to
remain over Kamchatka, resulting in the front occluding by the
time it reaches the Alaska Mainland. Temperatures are expected to
remain cold enough for snow over the mainland as the front moves
onshore Friday night. This system will also help to push out/erode
away some of the arctic airmass that has lingered over the state
for the past two weeks.

Behind this first, weaker system is a much more significant push
of warm air and moisture. The primary low is expected to form east
of Kamchatka and rapidly deepen. Some model solutions have this
low developing into a bomb cyclone with widespread rain and warm
temperatures spreading east across the Bering Sea. The timing of
the occlusion will determine the primary precipitation type over
the southwest mainland, but at this time there looks to be a
decent chance for freezing rain over interior areas before the
cold air catches up and turns the precipitation back to snow. For
Southcentral this could be a very significant southwest to
southerly flow snow event. With a more stout cold airmass ahead of
the moisture and the warm air being rapidly pushed to the south,
widespread snow appears likely at the start of next week.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Special Weather Statement 161
         Winter Weather Advisory 131 121 181
   Wind Chill Advisory 155.

MARINE...Storm Warning 411 413 130
 Gale Warning 351 352 412 414 150 155 160 165 170 171 172 174 175
176 177 178 180 120 131 132 138
Heavy Freezing Spray Warning 414
150 160 165 180 181 185 130 131 137 138 139.

FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MV
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CQ
MARINE/LONG TERM...CJ

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
303 PM AKST Tue Nov 30 2021

AKZ161-011500-
Bristol Bay-
Including the cities of King Salmon, Dillingham, Naknek,
and Pilot Point
303 PM AKST Tue Nov 30 2021

...BLOWING SNOW FOR PORT HEIDEN THROUGH WEDNESDAY MORNING...

Blowing snow with reduced visibility is expected for the extreme
southwestern portions of the Bristol Bay coast, particularly Port
Heiden. Cold, Arctic air wrapping around the back side of a low
in the Gulf of Alaska is expected to enhance snow showers and
gusty northwesterly winds across portions of the eastern Bering
Sea. These conditions will combine to produce blowing snow with
visibilities dropping to as low as one half mile at times.

Northwesterly winds 25 to 35 mph can be expected near Port
Heiden, with gusts to 45 mph at times. Snow shower activity,
along with the threat of low visibility, should diminish through
the morning hours as a drier airmass moves into the area, though
gusty northwesterly winds will persist through Wednesday
afternoon.