High Wind Watch 6, NWS Anchorage, AK

249 
WWAK71 PAFC 011850
NPWAER

URGENT - WEATHER MESSAGE
National Weather Service Anchorage AK
950 AM AKST Sun Nov 1 2020

AKZ111-020800-
/O.UPG.PAFC.HW.A.0006.201102T0300Z-201102T1800Z/
/O.EXB.PAFC.HW.W.0012.201102T0300Z-201102T1800Z/
Matanuska Valley-
Including the cities of Palmer, Wasilla, Sutton, and Chickaloon
950 AM AKST Sun Nov 1 2020

...HIGH WIND WARNING IN EFFECT FROM 6 PM THIS EVENING TO 9 AM
AKST MONDAY...

* WHAT...Northeast winds 35 to 45 mph with gusts up to 65 mph
  expected.

* WHERE...Matanuska Valley.

* WHEN...From 6 PM AKST this evening to 9 AM AKST Monday. Gusty 
  winds will continue to increase through the day and peak during 
  the evening and overnight hours. While the winds will gradually 
  diminish on Monday, they will remain gusty through at least 
  Tuesday.

* IMPACTS...High winds could move loose debris, damage property, 
  and cause power outages. Travel could be difficult, especially 
  for high profile vehicles.

* ADDITIONAL DETAILS...Blowing dust may also accompany these 
  strong winds. Wind chills near zero will be possible.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

People are urged to secure loose objects that could be blown
around or damaged by the wind. Prepare for the possibility of
widespread power outages. Use caution if you must drive.

&&

$$

AKZ131-020800-
/O.CON.PAFC.HW.W.0012.201102T0000Z-201102T1800Z/
Northeast Prince William Sound-
Including the cities of Valdez and Thompson Pass
950 AM AKST Sun Nov 1 2020

...HIGH WIND WARNING REMAINS IN EFFECT FROM 3 PM THIS AFTERNOON
TO 9 AM AKST MONDAY FOR THOMPSON PASS...

* WHAT...Northeast winds 35 to 55 mph with gusts up to 80 mph 
  expected.

* WHERE...Thompson Pass.

* WHEN...From 3 PM this afternoon to 9 AM AKST Monday. Gusty 
  winds will continue to increase through the day and peak 
  during the evening and overnight hours. Winds will remain 
  gusty through at least Tuesday.

* IMPACTS...High winds may move loose debris, damage property, 
  and cause power outages. Travel will be difficult, especially 
  for high profile vehicles.

* ADDITIONAL DETAILS...In addition to the winds, very cold 
  temperatures will also accompany the wind bringing wind chill 
  values as low as 30 below zero, especially tonight into early 
  Monday morning. Wind gusts to 55 mph are expected at the same 
  time in the town of Valdez.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

People are urged to secure loose objects that could be blown
around or damaged by the wind. Prepare for the possibility of
widespread power outages. Use caution if you must drive.

&&

$$

For more information from the National Weather Service visit
http://weather.gov/afc

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
508 PM AKDT Sat Oct 31 2020

.ANALYSIS AND UPPER LEVELS...

High pressure associated with an Arctic air mass continues to
build across all of mainland Southern Alaska this afternoon. In
addition to the coldest temperatures most areas have seen this
season, the air mass is also enhancing strong gap winds. Peak
winds so far this morning have reached 50 mph in Thompson Pass.
Winds are also gusty through Seward and Whittier as well. A bit
of fog worked its way into Bethel earlier this morning but that
has moved and is now largely confined to right along the
Kuskokwim Mountains. The leading front associated with a low
moving into the Western Aleutians is causing small craft winds
through Shemya as well. Finally, a couple bands of lake-effect
/Inlet-effect snow are prevalent on satellite over the southern
Cook Inlet, extending just east and offshore of Afognak Island,
with another smaller one off the western end of Kodiak Island.

In the upper levels, a deep positively tilted trough with 506 dm
low is digging southward into the area. The center of low is
between Bettles and Fort Yukon. Ridging is in place over the
central Bering, with the aforementioned surface and upper level
low moving into the Western Aleutians.

&&

.MODEL DISCUSSION...

Model agreement remains very good with most of the solutions
tightly clustered in the overall large-scale weather pattern.
There is very high confidence that precipitation outside of a
local scale snow shower in the mountains, will be non-existent.
So the primary foci today will be on the upcoming strong winds
through many of the gaps, and the falling temperatures. Forecast
confidence is very high, with somewhat less confidence on the
peak strength of the upcoming winds. Temperatures will be largely
determined by how strong the winds are; the lighter the winds,
the colder the temperatures.

&&

.AVIATION...
PANC...VFR conditions will persist. Occasionally gusty northerly
winds are expected for the rest of today through tonight,
increasing further in intensity during the day on Sunday. The
winds will peak overnight Sunday night into Monday morning with
gusts to 35 mph.

&&

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

The forecast precipitation wise across the area will remain very
quiet through the next three days as a dry and very cold air mass
for the end of October/start of November moves through the
region. The next couple of days will feature mainly sunny and dry
conditions with winds being the main issue. Winds will continue to
blow through the typical gaps over the next couple of days while
this air mass moves through Southcentral. Winds have increased
across much of Southcentral today with winds occasionally gusting
to 15-25 mph in Anchorage south to Kenai to Homer. The winds have
also made it into Valdez with winds sustained 10-20 mph with
gusts as high as 40-45 mph. The low temperature forecast for
tonight remains in question as a result of the winds. Where windy
conditions prevail, temperatures won't drop all that much
(although there will be a wind chill). However, where winds are
light, temperatures will be able to drop into the low single
numbers and even below zero due to radiational cooling and the
very cold air mass overhead.

A potent upper level wave is expected to move through Southcentral
beginning Sunday afternoon and continuing into Monday morning. As
a result, winds are expected to increase throughout the day across
the Matanuska Valley, peaking Sunday night into Monday morning as
the upper level support will be in place as well as the very cold
air mass over the Copper River Basin to help push the air down the
Glenn Highway and into the Valley. A Special Weather Statement was
sent for this setup with sustained winds of 40-55 mph possible and
gusts as high as 65 mph. Due to the cold temperatures combined
with the wind, wind chills may reach as low as 10 below zero at
times.

Next, a High Wind Watch was issued for Thompson Pass for sustained
winds of 40-55 mph and gusts to 75 mph possible Sunday afternoon
to Monday evening. The one thing that warranted this watch is the
pressure gradient that will be setup across the region. A very
cold air mass and high pressure in the Copper River Basin and low
pressure over the Pacific will cause the cold air to drain through
the gaps and passes. There are some things working against this
such as southerly upper level flow and waning cold air advection.
However, felt pressure gradients were impressive enough to issue
the Watch.

Winds will also come up across the Anchorage Bowl especially for
Monday as the pressure gradient tightens across Southcentral.

&&

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

The potential of snowfall and very cold overnight temperatures
between 5 to 15 degrees Fahrenheit (and may be much lower than 5
degrees in some areas) are the highlights for Southwest Alaska in
the next few days. A shortwave just offshore of Hooper Bay will
race southeastward through Bristol Bay tonight. Meanwhile, another
separate shortwave connected to an upper level trough from Norton
Bay will dive southward across Southwest Alaska overnight tonight,
then across the AKPEN into the Pacific Sunday evening. The latter
shortwave could enhance snow over AKPEN starting Sunday. In
response to this upcoming feature, temperatures at 850 mb east of
Lime Village and north of Port Alsworth will drop to between -20
to -25 degrees Celsius starting Sunday morning if not sooner. Over
Bristol Bay, northerly winds with gusts up to 35 to 40 mph will
lead to an expanding area of freezing spray across Bristol Bay
and along the Alaska Peninsula. Overall, it'll be a relatively
quiet forecast period for SW Alaska.

&&

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

Gales from a frontal system over the western Aleutians will spread
across the central Aleutians Sunday and Sunday night. The Northwest
Pacific low connected to this frontal boundary will stay south of
the Aleutians through the forecast period, so it will be a quiet
forecast period once the gales exit from the area Sunday night
into Monday. A developing trough from the northern Bering could
elevate seas and weather on Tuesday, but it is too soon to
speculate what this next system would do. Stay tune and will
provide updates as future model runs become available.

&&

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

A reinforcing shot of cold air will dive southward across western
Alaska Tuesday, then across the Alaska Peninsula Tuesday night and
Wednesday. Gale force winds are likely across the Southwest Alaska
marine zones, while gusts on the south side of the Alaska Peninsula
could reach storm force. Some of these stronger winds will shift
into the Gulf on Wednesday, then slowly diminish Wednesday night
through Thursday.

Meanwhile, a deep low will track across the Kamchatka Peninsula,
pushing a strong front eastward across the Bering Sea and
Aleutians Tuesday through Wednesday and reaching the Southwest
Alaska coast on Thursday. The forecast largely reflects gale force
winds with this front. However, it is looking more and more like
there will be some storm force winds as the front crosses the
western to central Bering Sea.

&&

.LONG TERM FORECAST (Days 4 through 7/Wednesday through Friday)...

The long term forecast begins midweek with a persistent upper-
level, long-wave trough over the state with an upper-level ridge
cresting over the far western Bering and Aleutians. At the
surface, this translates to a strong ridge of high pressure
extending across interior Alaska and a surface trough stretched
out over the northern Gulf. This pattern has resulted in generally
clear skies and frigid temperatures due to the light northerly
flow ushering in arctic air and deepening the column of cold air
over much of the Southern Mainland. This has been the dominant
weather feature over the past couple of days and will remain the
trend into the latter half of next week. By Wednesday, a shortwave
diving south over the eastern Bering will track over the AKPEN,
resulting in an increase in snow showers from coastal Southwest
Alaska to the eastern Aleutians. A surface low is also expected
to spin up near Kodiak Island which will help enhance both the
thermal and pressure gradients, leading to an increase in
northerly gap winds along the AKPEN. This feature will slide
quickly to the south, entering the far southern Gulf by Wednesday
evening. However, the ridge over the interior will strengthen,
leading to the potential for increased outflow winds along the
Southcentral coast through late Thursday.

Guidance, however, is suggesting a pattern change may be in store
following the passage of the aforementioned shortwave.
Specifically, the long wave pattern looks to amplify and progress
eastward by the weekend as a deepening upper-level trough digs
over west Asia and shifts the upper-level ridge over the Aleutians
and trough over Mainland Alaska east. At the surface, this shift
will result in the surface ridge over the Aleutians sliding south
and east, allowing a deep low to spin up off of Kamchatka and lift
a front over the Bering toward Southwest Alaska by late Thu. This
solution would also increase the southwesterly flow and introduce
an increased chance for mixed precipitation along the Southwest
coast with snow over the interior. Guidance then suggests that
this front, or remnants of it, may attempt to work into Southcentral
by the end of the week as the ridge once over the Aleutians moves
to the Gulf and the ridge over the interior weakens and moves
farther east over the Yukon and Northwest Territories. There is a
bit of disagreement within the models, however. First, the EC is
not as amplified as the GFS and weakens the Kamchatka low and
associated front more quickly, with the front breaking apart
before it has a chance to move inland. Second, as the ridge moves
into the Gulf, there are strength and timing discrepancies with
the potential of another storm system spinning up and moving
toward the AKPEN for early next week. Nonetheless, the shift in
the pattern looks to bring a more southerly flow, warmer
temperatures, and increased chances for mixed precipitation to
Southwest Alaska by the end of the weekend. As for Southcentral,
there is also a chance for increased cloud cover and precipitation
by the end of next weekend. However, there is much less
confidence on this as any storm system would have to break down
the cold ridge currently in place. Models are notorious for trying
to break these stagnant ridges down too quickly. Nevertheless,
the shift in the pattern would result in a decrease in the
northerly flow and a slow warm up in temperatures both aloft and
at the surface across Southcentral by the end of next weekend.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Watch 131.
MARINE...Gale Warning 121 125 126 127 128 129 130 131 132 139 140
                      174 176 177 178.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...JW
SOUTHCENTRAL ALASKA...MV
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB
MARINE/LONG TERM...SB/MK/TM