Winter Storm Watch 6, NWS Anchorage, AK

022 
WWAK41 PAFC 160105
WSWAER

URGENT - WINTER WEATHER MESSAGE
National Weather Service Anchorage AK
405 PM AKST Mon Nov 15 2021

AKZ141-160215-
/O.CAN.PAFC.WS.A.0006.211117T0300Z-211118T0300Z/
Copper River Basin-
Including the cities of Glennallen, Eureka, McCarthy, Paxson, 
and Slana
405 PM AKST Mon Nov 15 2021

...WINTER STORM WATCH FOR AREAS SOUTH AND EAST OF GLENNALLEN IS 
CANCELLED...

Light snow is still expected across the southern and eastern
Copper River Basin late Wednesday through Thursday. However, the
heaviest snow is now expected to remain east of the area. Minor
accumulations of 1-3 inches are still possible, but amounts will
likely remain below advisory or warning criteria. 

$$

AKZ145-161500-
/O.EXT.PAFC.WC.Y.0008.211117T1000Z-211118T2100Z/
Susitna Valley-
Including the cities of Talkeetna, Willow, and Cantwell
405 PM AKST Mon Nov 15 2021

...WIND CHILL ADVISORY NOW IN EFFECT FROM 1 AM WEDNESDAY TO NOON
AKST THURSDAY...

* WHAT...Very cold wind chills expected. Wind chills as low as 
  50 below zero.

* WHERE...Broad Pass.

* WHEN...From 1 AM Wednesday to noon AKST Thursday.

* IMPACTS...The dangerously cold wind chills could cause 
  frostbite on exposed skin in as little as 10 minutes.

* ADDITIONAL DETAILS...Winds to 25 mph with gusts up to 40 mph
  combined with temperatures between 10 and 25 below through Broad
  Pass will cause dangerously wind chills both overnight Tuesday
  into Wednesday morning and Wednesday night into Thursday 
  morning.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Use caution while traveling outside. Wear appropriate clothing, a
hat, and gloves.

&&

$$

http://www.weather.gov/afc

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
505 PM AKST Sun Nov 14 2021

.ANALYSIS AND UPPER LEVELS...

A potent low is currently located over the central Gulf and
continues to track southeastward towards Southeast AK. This low is
responsible for increasing the offshore gradient, especially in
the typical locations of Whittier and Seward. This has also led to
some blowing snow and visibility to 2 miles in Whittier early
today. Patchy fog and low stratus plagued areas of the Matanuska
Valley, Anchorage Bowl, and Kenai Peninsula this morning before
seeing it burn off some this afternoon. Temperatures dropped as
low as -15F in the Copper River Basin overnight. The thermal
gradient that has developed from this cold airmass inland vs the
still-warm SSTs over the Gulf (~45F) is helping to induce some
gusty winds through the gaps as well. Places like Thompson Pass
are already gusting to 45 mph.

A ridge of high pressure at upper levels is building over the
eastern Aleutians and Alaska Peninsula while an upper level low is
located over the western Bering. As the low progresses eastward,
the leading frontal boundary continues to produce gale-force
gusts and light rain along the Aleutian Chain.

&&

.MODEL DISCUSSION...

Models remain in remarkably good agreement with the overall
pattern and major synoptic features. The struggle for today's
forecast has been the timing of the fog/stratus burn off. Any
redevelopment of the fog/stratus tonight should be more limited
with a continued offshore gradient and another day of drying. We
still can't rule it out completely, so hand edits were use to
address this concern. The other main area of focus centers on a
strong upper level low dropping from the Interior of AK south
across the AK Range Wed (into Thu). The important thing to note
here is that all the models AGREE on this synoptic pattern. There
are actually very few differences between the models at this time,
which results in high forecast confidence. Much of the time for
the next several forecast packages will be spent refining the
details for this upcoming pattern.

&&

.AVIATION...
PANC... Fog and stratus will continue to lurk near Knik Arm. While
conditions should be able to remain VFR with light N-NE winds
through the daylight hours, a chance remains that stratus/fog
could move back in overnight. The odds of this are less than Sun
morning, but confidence is only low to moderate in any exact
timing or restrictions.

&&.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Tonight through Wednesday)...

High pressure over the area will be the name of the game for the
next several days. As the upper arctic low descends south from
mainland Alaska Tuesday night through Wednesday, the forecast for
further cooling and gusty gap winds will need special attention as
the pattern develops with time. Although the upper-level
vorticity appears quite energetic on the western and southern
portions of this low, its overall placement leaning more west will
limit any further cooling and higher gap winds through the Copper
River Basin to the North Gulf coast, at least initially.
Consequently, Valdez and Thompson pass winds will be a little more
tricky as the upper level winds oppose the direction of the
surface gradient. None the less, with the cold air mass in place,
expect winds to be gusty at times. Given the location of the
vorticity max along with tropospheric folding and topography
around the western Gulf, winds out of the Barren Islands will near
the upper end of storm force with hurricane force gusts and
increase the potential for heavy freezing spray. Any snowfall
around the southern Kenai peninsula (Seldovia area) could lower
visibilities.

Localized winds and any fog will be the only factors that could
keep the temperatures slightly higher, but for most areas, the
combination of clear skies, light winds, a deep snowpack, and a
persistent and cooling air mass will allow many areas across
interior Southcentral to see temperatures drop to 20 to 30
degrees below average, which will mean 20 to 30 degrees below zero
for the coldest areas of the Copper River Basin. Any wind could
result in wind chills as low as 30 to 40 below. Temperatures over
the remainder of Southcentral are likely to be around 15 degrees
below average.

&&

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

Cold and clear conditions continue as surface high pressure
persists over Alaska. A warm front, extending from a low in the
Bering Sea, will approach Southwest tonight into tomorrow morning.
Increased winds associated with this front will allow warmer air
from aloft to mix downward, mitigating cooling at the surface.
While skies will remain mostly clear, cirrus clouds ahead of the
front will also reduce nighttime radiational cooling. As such,
tonight's nighttime lows are expected to dip no lower than single
digit negatives.

Temperatures return to a downward trend Tuesday as an upper level
polar low moves southward from the Arctic Ocean into Alaska.
This upper level low combined with surface high pressure over
land will draw cold, Arctic air into the Southwest. Minimum
temperatures will once again dive into the double digit negatives
Monday and Tuesday night. The coldest temperatures will be in the
Lower Kuskokwim Valley Tuesday night, where temperatures of -20F
or lower are expected. As this cold, dense air funnels through
lower terrain and towards the coast, the combination of near-
freezing sea surface temperatures, stronger winds, and subzero
temperatures could lead to freezing spray offshore.

&&

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

Unsettled conditions are in store for the Bering Sea and the
Aleutians as the active storm track brings several lows through
the Bering Sea. The first low is currently pushing a warm front
across the Eastern Aleutians and AKPEN, where it will bring light
to moderate rain and southerly winds. Cold air wrapping around the
back side will produce gale-force winds and the potential for
rain showers as it moves along the Western and Central Aleutians.
Conditions become more benign Monday evening as the low crosses
the AKPEN and another low forms in the North Pacific at the triple
point.

For Tuesday and Wednesday in the AKPEN, the newly formed triple
point low will draw cold, Arctic air southward from the interior.
This will drive gusty gap winds and bring the potential for
freezing spray south of AKPEN. Along the Aleutian Chain,
conditions on Tuesday and Wednesday will be influenced by another
incoming warm front and the ridge preceding it. The ridge will
bring partly cloudy skies and lighter winds as it transits across
the Chain. Behind it, a warm front extends off a low near the
Kamchatka Peninsula. With weak upper level support, rain chances
and winds will diminish by the time the front approaches the
Eastern Aleutians Tuesday night.

&&

.MARINE (Days 3 through 5: Wednesday through Friday)...
Gulf of Alaska...On Wednesday, a digging trough will push cold,
Arctic air offshore, driving strong winds out of gaps along the
Gulf coast and contributing to the formation of a low in the
northern Gulf. These gap winds will reach storm force and produce
heavy freezing spray, especially in the vicinity of Kamishak Bay
and the Barren Islands. Mariners should take heed of this freezing
spray potential as it could be an extreme event. The only variable
that is not ideal for freezing spray is still warm SSTs across
parts of the Cook Inlet. Winds will diminish through Friday as
the low and upper- level trough move into the eastern Gulf. Seas
remain below 20 ft.

Aleutians/Bering...Localized areas of gales are possible near the
center of a low in the western Bering/Aleutians on Thursday. Its
front pushes northward and may develop a more widespread swath of
gales in the western and central Bering Thursday night. Seas
remain below 20 ft.

.Long Term Discussion (Days 4 through 7: Thursday through Sunday)...

Confidence is increasing that an upper-level low digs over
Southcentral, dropping into the Gulf by Thursday, leading to a
blast of cold, Arctic air for southern Alaska. Temperatures look
to reach their coldest on Thursday night, when most of the
southern mainland could see temperatures 20 to 30 degrees below
normal in locations where skies remain clear. Cold air advection
will also enhance gap winds, keeping temperatures warmer in those
coastal areas with increased mixing. A low in the Gulf on Thursday
may squeeze out some lingering moisture along the north Gulf
coast in the form of snow. Elsewhere, conditions are dominated by
Arctic high pressure, so little precipitation and mostly clear
skies are expected through the end of the week.

Model guidance is in good agreement that both the Gulf low and the
upper- level low will eject eastward by Saturday, with offshore
flow weakening through the weekend. Guidance diverges beyond this
point with the next trough digging southward across the state. How
far west the trough is located, ranging from the eastern Bering
to over Southcentral in various model solutions, will have an
impact on temperatures this weekend. The GEM keeps temperatures
well below normal with a further east solution, while the GFS and
EC place the trough further west, allowing a weak ridge to pass
aloft and low-level southerly flow allowing a warmer air mass to
slowly work its way in over parts of the Southern mainland.

Out west, a high amplitude ridge persists over the eastern Bering,keeping
the storm track in the western and central Bering through at
least Friday night. Models tend to break down this ridge over the
weekend as a result of the second digging trough, with the GFS and
EC bringing colder air streaming over the Bering from the Alaska
mainland.

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 127 177 178 185.
	 	 Heavy Freezing Spray Warning 140 160 180 181.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MSO
SOUTHCENTRAL ALASKA...AP/VR
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KC
MARINE/LONG TERM...CQ