High Wind Watch 8, NWS Anchorage, AK

873 
WWAK72 PAFC 211300
NPWALU

URGENT - WEATHER MESSAGE
National Weather Service Anchorage AK
400 AM AKST Sat Dec 21 2019

AKZ185-211400-
/O.CAN.PAFC.HW.A.0008.191222T1800Z-191223T0900Z/
Eastern Aleutians-
Including the cities of Unalaska and Nikolski
400 AM AKST Sat Dec 21 2019

...HIGH WIND WATCH IS CANCELLED THROUGH SUNDAY EVENING...

Winds should stay below 75 mph, as strongest winds are now 
expected to stay north of the Eastern Aleutians. 

$$

AKZ187-220200-
/O.CON.PAFC.HW.W.0013.191222T0700Z-191223T0100Z/
Central Aleutians-
Including the city of Atka and Adak
400 AM AKST Sat Dec 21 2019

...HIGH WIND WARNING REMAINS IN EFFECT FROM 10 PM THIS EVENING TO
4 PM AKST SUNDAY...

* WHAT...West winds 45 to 55 mph with gusts up to 85 mph 
  expected.

* WHERE...Central Aleutians.

* WHEN...From 10 PM Saturday to 4 PM AKST Sunday.

* IMPACTS...High winds may move loose debris and damage property.
  Travel will be difficult.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

People are urged to secure loose objects that could be blown
around or damaged by the wind. 

&&

$$

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

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
755 AM AKST Fri Dec 20 2019

.ANALYSIS AND UPPER LEVELS...
An arctic airmass has moved into southwest Alaska but has
met resistance from the Alaska Range. Where the skies were clear
over night, radiational cooling occurred and a number of locations
in southcentral dipped into the teens and single digits. The
thermal gradient is pretty stark on each side of the Alaska Range.
As of 4 AM the temperature in Skwentna was 10 degrees Fahrenheit
while the temperature was -35F at McGrath. On satellite imagery,
there is an elongated cloud shield from NE Russia that crosses the
Bering Straight, clips Western Alaska and the Eastern Aleutians.
Light precipitation from this frontal boundary has been detected
on the Bethel Radar (PABC) near Kipnuk and Toksook Bay.
ASCAT/advanced scatterometer has detected gale force winds in the
Bering associated with this low pressure system. Last but not
least, there is a 980mb low southwest of Sitka with an inverted
trough extending northward into Prince William Sound. The
Middleton Island Radar (PAIH) has detected showers south of
Chenega and showers near the Copper River delta associated with
this feature.

&&

.MODEL DISCUSSION...
Models remain in good synoptic agreement through Sunday. The
ensemble members of the GFS continue to be tightly grouped
through 12z Sunday but then divergence emerges with the ensemble
members. Both the ensembles and the deterministic models, indicate
a major pattern change next week for southcentral Alaska.

&&

.AVIATION...

PANC...VFR conditions and light winds are likely to persist.
However, there is the potential for fog and low stratus to again
form along the Knik Arm later this morning. If this does occur, a
light northerly wind may transport any fog / low stratus into the
aerodrome. Confidence in this is low, however, kept VCFG to the
TAF package for PANC.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

Generally dry and gusty offshore flow will continue through
Saturday. Cold advection across Southcentral will continue strong
thermal and pressure gradients through today which has giving
rise to strong outflow conditions across the western Gulf, coastal
locations along the northern Gulf, as well as, local gap flows
inland. Winds will diminish some today, but will strengthen again
late tonight and into Saturday as cold air pours over the
mainland. Temperatures are expected to fall below zero in many
places across Southcentral tonight with the coldest readings in the
minus 30s in the Copper River Basin. The one thing that could push
temperatures to the warmer side tonight and Saturday west of the
Copper River Basin would be if an upper wave moving into the area
thickens the cloud cover.

&&

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

A front is moving into Southwest Alaska this morning. Light snow
is ongoing across much of the Kuskokwim Delta west of Bethel. the
snow will continue moving east through the morning, with 1 to 3
inches of snow possible for most of the Kuskokwim Delta. The front
will weaken rapidly as it tries to cross the Kuskokwim Mountains.
The portion of the front moving across Bristol Bay will continue
into the King Salmon area late this afternoon and evening, with an
inch or so of accumulation possible. Elsewhere, snow showers
producing not much more than a dusting of accumulation are
possible through the Lower Kuskokwim Valley this evening.

Behind the front, snow showers will move in from the Bering on a
reinforcing cold air mass. However, with lingering cloud cover
from the front persisting, temperatures are not expected to
respond much. Thus, expect more of the same temperature-wise, with
temperatures staying sub-zero over the Lower Kuskokwim Valley,
with single digits and teens possible for highs over the Kuskokwim
Delta and Bristol Bay.

By Saturday, the winds will slacken off and eventually turn
southeasterly by the afternoon along the coast. This will end the
threat of snow showers away from the mountains. The southeasterly
winds are in response to the next much stronger front which will
move into Southwest Alaska on Sunday. Unlike the current front,
the one on Sunday will have much more moisture with it, but track
into the area from the south. Despite the moisture and warmer air
with it, near the surface, the winds will remain out of the
north, keeping cold air in place. Thus, precipitation type will
not be an issue with this as we can confidently say everything
will fall as snow. With that said, how much moisture can be wrung
out as snow and if there is an easterly downslope component
cutting into the snowfall totals around King Salmon are questions
that remain to be answered in future forecasts. What can be said
right now is that this does not look to be an event that will
produce large amounts of snow. The primary area that will get
snow out of this will be along Bristol Bay, as the front stalls
out before getting to spread much moisture any further north.
Behind the low another temperature plunge with a reinforcing shot of
Arctic air is expected going into the start of the upcoming holiday
workweek.

&&

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

High pressure over the western and central Aleutians this morning
will rapidly translate east as a rapidly strengthening low follows
behind the high. The low will start to make its presence known
across the Western and Central Aleutians tonight. In advance of
the low, warm air on strong southeasterly winds will produce
moderate rain with gusts up to 65 mph over Adak and Atka. To the
north and west of the low, Shemya and the western Aleutians should
mainly be snow for this low. With the center of the low tracking
well east of Shemya, the island is unlikely to experience high
winds, though gusty winds, frequent snow showers, and temperatures
around freezing won't make things pleasant there by any means. The
center of the low will track west of Adak Saturday morning. Behind
the low, very strong westerly winds will transport colder air over
the area. However, it's the winds that will be the primary weather
story. Since the low will still be strengthening through the day
Saturday, hurricane force wind gusts are likely across the Rat and
Andreanof Islands, including Adak and Atka. Those winds will hold
off in Adak and Atka until Saturday night. Thus, a High Wind Watch
has been issued for the central Aleutians. As the low center slows
and turns eastward, the high winds will impact Atka through much
of the day Sunday.

With the cold air wrapping around the south side of the low on
strong westerly winds, precipitation will change over to snow.
However, before the coldest air gets there, the snow will largely
end. Thus, it appears most of the snow, or rain/snow mix, will
fall before the strongest winds get there. This separation in time
greatly reduces the threat for blizzard conditions. With that
said, frequent snow showers over the Western and Central Aleutians
will reduce visibilities in the very strong winds to 1 mile at
times.

The low will approach the Pribilof Islands on Sunday, as it begins
to weaken. Since the Pribilofs will stay on the warm side of the
low, hazardous weather is not expected. However, strong winds and
seas are likely in the area. The weakening low center will track
south of the Pribilofs Sunday afternoon and evening, but strong
winds with frequent snow showers may potentially impact the Dutch
Harbor area in that time frame as well.

&&

.MARINE (Days 3 through 5)...
A storm force low will track from the western Aleutians to the
southern Bering Sea Saturday into Sunday. Expect widespread storms
and gales over the Bering and Aleutians, with the strongest winds
on the south side of the low, i.e., near the Aleutians with 40
foot combined seas possible. Farther east, Arctic high pressure
inland will facilitate strong offshore flow along the North Gulf
Coast. Expect gusty winds over the Barren Islands and out of the
Copper River Delta, Resurrection Bay and in the Valdez
Narrows/Valdez Arm Sunday. Conditions will become more benign
Monday into Tuesday... the Bering low will weaken and move inland,
and several weaker lows will develop in the Gulf.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Beginning the extended period forecast on Sunday, the regional
upper air pattern will already be undergoing a rather dramatic
change as the mainland will be dominated by arctic troughing. This
is a huge change from the last several months (arguably, the
last year and a half) which has seen incredible and unprecedented
anomalous upper level ridging. Over the Bering Sea, there will be
a weakening storm force low with the front moving into the Gulf
of Alaska as a triple point low by Sunday afternoon and evening.
Besides below average temps over the entire Mainland, expect
increasing threats for accumulating snowfall as these warm fronts
move up along the North Gulf Coast, in conjunction with an arctic
trough over the western half of the Mainland. By Monday, large
enough differences among the global models lends to increasing
disagreement with the placement of a mainland arctic trough, which,
as usual, dictates snowfall potential inland. The ECMWF is most
bullish developing an arctic trough farther south across Southwest
Alaska whereas the GFS and Canadian develop it farther north, which
effectively allows for more southeast cross-barrier flow and warmer
temps. The ECMWF would result in colder temps lasting all week,
along with much higher chances for accumulating snow across large
swaths of the Mainland. The GFS and Canadian also support snow, but
would be more localized and harder to predict in their projected
patterns. The takeaway: wintry weather is here for the Christmas
holiday week and the potential for accumulating snowfall exists
across the entire southern Mainland region. Expect an active low
track along the Aleutian Chain as well as colder air shunts the
storm track southward.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Watch 187.
MARINE...Storm 413 412 173 175 176 177 178. Gale 121 127 130 131
132 138 351 352 170 171 172 174 179 411 414. Heavy Freezing Spray
181.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...RC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JW
MARINE/LONG TERM...MM/JA