Winter Storm Watch 16, NWS Anchorage, AK

076 
WWAK41 PAFC 210126
WSWAER

URGENT - WINTER WEATHER MESSAGE
National Weather Service Anchorage AK
426 PM AKST Mon Dec 20 2021

AKZ131-211430-
/O.UPG.PAFC.WS.A.0016.211221T1000Z-211222T0000Z/
/O.NEW.PAFC.BZ.W.0026.211221T1000Z-211222T0100Z/
Northeast Prince William Sound-
Including the cities of Valdez and Thompson Pass
426 PM AKST Mon Dec 20 2021

...BLIZZARD WARNING IN EFFECT FROM 1 AM TO 4 PM AKST TUESDAY FOR
THOMPSON PASS...

* WHAT...Blizzard conditions expected. Total snow accumulations of
  1 to 3 inches. Winds could gust as high as 70 mph. 

* WHERE...Thompson Pass.

* WHEN...From 1 AM to 4 PM AKST Tuesday.

* IMPACTS...Plan on slippery road conditions. Visibility reduced
  to one quarter mile or less at times.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A Blizzard Warning means severe winter weather conditions are
expected or occurring. Falling and blowing snow with strong winds
and poor visibilities are likely. This will lead to whiteout
conditions, making travel very hazardous. If you must travel,
have a winter survival kit with you.If you get stranded, stay
with your vehicle. 

For the latest road conditions call 5 1 1 or visit
511.alaska.gov.

&&

$$

AKZ101-211000-
/O.CON.PAFC.WW.Y.0071.000000T0000Z-211221T1000Z/
Anchorage-
Including the cities of Anchorage, Eagle River, Indian, 
and Eklutna
426 PM AKST Mon Dec 20 2021

...WINTER WEATHER ADVISORY REMAINS IN EFFECT UNTIL 1 AM AKST
TUESDAY...

* WHAT...Snow. Additional snow accumulations of 4 to 8 inches.
  Highest amounts are expected across East Anchorage, the
  Hillside, Eagle River and the Glenn Highway corridor.

* WHERE...Anchorage.

* WHEN...Until 1 AM AKST Tuesday.

* IMPACTS...Plan on slippery road conditions. The hazardous
  conditions could impact the morning and evening commute.
  Visibility reduced to one half mile or less at times.

* ADDITIONAL DETAILS...Freezing drizzle currently falling over the
  Anchorage Bowl will quickly change over to all snow by early
  this evening and become steadier and heavier. 

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Slow down and use caution while traveling.

For the latest road conditions call 5 1 1 or visit
511.alaska.gov.

&&

$$

AKZ111-211000-
/O.CON.PAFC.WW.Y.0071.000000T0000Z-211221T1000Z/
Matanuska Valley-
Including the cities of Palmer, Wasilla, Sutton, and Chickaloon
426 PM AKST Mon Dec 20 2021

...WINTER WEATHER ADVISORY REMAINS IN EFFECT UNTIL 1 AM AKST
TUESDAY...

* WHAT...Snow. Additional snow accumulations of 4 to 8 inches. 
  Highest amounts from Palmer north and east including Sutton to 
  Chickaloon.

* WHERE...Matanuska Valley.

* WHEN...Until 1 AM AKST Tuesday.

* IMPACTS...Plan on slippery road conditions. The hazardous
  conditions could impact the evening commute. Visibility reduced
  to one half mile or less at times.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Slow down and use caution while traveling.

For the latest road conditions call 5 1 1 or visit
511.alaska.gov.

&&

$$

AKZ121-210600-
/O.CON.PAFC.WW.Y.0071.000000T0000Z-211221T0600Z/
Western Kenai Peninsula-
Including the cities of Kenai, Soldotna, Homer, 
and Cooper Landing
426 PM AKST Mon Dec 20 2021

...WINTER WEATHER ADVISORY REMAINS IN EFFECT UNTIL 9 PM AKST THIS
EVENING...

* WHAT...Snow, mixed with freezing rain at times. Total snow 
  accumulations of 2 to 5 inches and ice accumulations of around 
  one tenth of an inch. Highest snow amounts from Sterling east.

* WHERE...Western Kenai Peninsula.

* WHEN...Until 9 PM AKST Monday.

* IMPACTS...Plan on slippery road conditions. The hazardous
  conditions could impact the evening commute. 

* ADDITIONAL DETAILS...Rain in Homer will transition to snow this
  evening. 

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Slow down and use caution while traveling.

For the latest road conditions call 5 1 1 or visit
511.alaska.gov.

&&

$$

AKZ141-211200-
/O.CON.PAFC.WW.Y.0071.000000T0000Z-211221T1200Z/
Copper River Basin-
Including the cities of Glennallen, Eureka, McCarthy, Paxson, 
and Slana
426 PM AKST Mon Dec 20 2021

...WINTER WEATHER ADVISORY REMAINS IN EFFECT UNTIL 3 AM AKST
TUESDAY...

* WHAT...Snow. Total snow accumulations of 4 to 8 inches.

* WHERE...Copper River Basin.

* WHEN...Until 3 AM AKST Tuesday.

* IMPACTS...Plan on slippery road conditions. Visibility reduced
  to one half mile or less at times.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Slow down and use caution while traveling.

For the latest road conditions call 5 1 1 or visit
511.alaska.gov.

&&

$$

http://www.weather.gov/afc

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
447 PM AKST Sun Dec 19 2021

.ANALYSIS AND UPPER LEVELS...

The weather over southern Alaska late this afternoon revolves
around a large North Pacific ridge that has its axis over the
eastern Bering Sea and northward toward the Bering Strait. The
250 mb jet stream is running up and over the northern part of the
ridge and then turns back toward the southeast bringing northerly
flow aloft over southcentral Alaska this afternoon and evening.
This is a fairly strong jet with speeds around 140 to 160 kts.
Ahead of this ridge, a shortwave is over the Copper River Basin
and heading toward the Alcan border. the subsidence behind the
shortwave and ahead of the amplifying ridge is keeping widespread
stratus over Coon Inlet through the Susitna Valley.

A strong surface low just east of Kamchatka is interacting with
the surface ridge over Southwest Alaska to bring in a strong
southwesterly flow for both the surface and aloft over most of the
Bering Sea which is increasing the amount of warm air flowing int
the region.

&&

.MODEL DISCUSSION...
Models are in good synoptic agreement in the Southcentral and
Southwest mainland Alaska regions into the middle of next week.
The main issue is with some important differences in temperatures
aloft which will impact precipitation- type, especially in
Southwest AK and the southern Kenai Peninsula. An example of this
can be seen with the MOS temperature for Homer on Monday. The
latest data for the GFS and NAM show a 14 degree difference in
expected high temperatures with one in the lower 30s and keeping
precip all snow and the other in the mid 40s with rain.

For the Bering Sea and Aleutians models are also in good synoptic
agreement through the weekend, but by Monday night there is a
significant spread in the track and intensity of the low moving
into the southwest Bering Sea from the North Pacific. As long as
the GEM is not used, the differences can be adjusted to give a
reasonable forecast for the Bering/Aleutians from the other models

&&

.AVIATION...
PANC...MVFR ceilings are likely to persist through the evening.
They may rise to around 4000 ft around midnight with a short wave
that could reduce the subsidence over the area.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Tonight through Wed afternoon)...

A transient upper level ridge continues moving eastward through
Southcentral tonight. The ridge is expected to crest over the area
this evening before heights begin to fall as the next upper level
shortwave begins its approach for Monday. Therefore, underneath
this ridge has been low stratus with areas of flurries as moisture
remains in the lowest levels of the atmosphere. This is expected
to remain the case throughout the evening and overnight hours.
Areas of patchy fog are expected as well for places such as Kenai,
Soldotna, as well as Anchorage and the Matanuska Valley. There is
also the potential this low stratus squeezes out some flurries
and therefore, this was left in the forecast this update. Also,
looking at the 00z sounding for Anchorage, there is a dry layer
from 850 mb all the way up to 300 mb. This is a signal for light
freezing drizzle. As a result, keep an eye out for patchy spots of
potential light freezing drizzle this evening and overnight.
Temperatures are also expected to remain fairly steady state as a
result mostly in the teens to around 20 degrees. The coldest spot
will be the Copper River Basin with temperatures single numbers to
potentially below zero.

Next, onto the weather maker for Southcentral Monday. After the
ridge crests over the area this evening, deep west-southwesterly
flow will develop on the backside as a vigorous upper level
shortwave trough moves through Southwest and across the Alaska
Range for Monday. This will advect more moisture north up the Cook
Inlet region into the Susitna Valley. As a result, expect light
snow to develop and overspread much of Southcentral Monday
morning and remain fairly light until the upper level shortwave
trough with the better lift and instability approaches midday
Monday. This will result in increased lift in the atmosphere
which will intensify the snowfall rates for the Anchorage Bowl,
Anchorage Hillside and Matanuska Valley. On top of all this,
precipitation type will be an issue. For Homer, still expect
enough warm air through a deep column of the atmosphere to keep
mostly rain for the area. However, as warm air moves northward
along the Kenai Peninsula, the warm layer will become less thick
with temperatures at the surface at to below freezing. Therefore,
snow and freezing rain is expected for places such as Kenai,
Soldotna, along the Sterling Highway east to Cooper Landing and
south to Clam Gulch. Therefore, see Winter Weather Advisory for
more details.

For Anchorage, the warm air layer will be thinner resulting in
mostly snow with occasional snow grains or snow pellets. 4 to 8
inches of snow is expected across Anchorage with the highest
amounts on the Hillside. See Winter Weather Advisory for further
details. For the Matanuska Valley, expecting mostly snow including
for Hatcher Pass with 5 to 10 inches valley floor and 8 to 12" for
Hatcher. Highest amounts Palmer north and east including Sutton
and Chickaloon. See Winter Weather Advisory for more details. One
last thing of note will be colder air will move back in on the
backside and the snow will become a drier and more powdery
consistency.

Snow will also overspread the Copper River Basin and eastern
Prince William Sound Monday afternoon through Tuesday morning.
Snowfall amounts here are expected to range from 2 to 4 inches.

Strong cold air advection is expected in the wake of the trough
overnight Monday through the day Tuesday with strong gusty winds
expected through the typical gaps wind areas (i.e. Seward,
Whittier, Valdez, Thompson Pass, Barren Islands area, and Shelikof
Strait).

&&

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

Scattered rain showers continue across Southwest Alaska this
evening ahead of a cold front beginning to move onshore the
Kuskokwim Delta coast. With temperatures in the mid 30s across
most of Southwest Alaska, and warm air streaming aloft ahead of
the front, precipitation is expected to be primarily rain as it
pushes eastward across Southwest tonight into Monday morning.
Portions of the Kuskokwim Delta and Lower Kuskokwim Valley may see
some snow mix in with the rain on the tail end of the strongest
precipitation as temperatures begin to cool, but for most areas
the coldest air will be too far behind the front to see rain
transition back to snow.

Colder, northwesterly flow behind the front will bring back 20s
and 10s across Southwest Monday night. Along with cooler
temperatures, a strong upper shortwave coupled with a surface
trough produces some scattered snow showers through the Kuskokwim
Delta Monday evening and reaches the Lower Kuskokwim Valley by
early Tuesday morning. Tuesday keeps cool and dry with surface
high pressure moving in off the eastern Bering.

However, by Tuesday night, the next round of snow begins as a
front moves in along the Southwest coast. This looks to be the
next forecast challenge, with more questions about precipitation
type. The warm air behind this front should be drawn up from the
North Pacific by an occluding low in the far western Bering and a
much colder airmass is expected to be in place over Southwest than
with today's event. This lends to the present thinking for this
forecast package that precipitation will stay all snow through
Wednesday for inland areas, though locations near the coast may
experience a wintry mix. There remains uncertainty regarding the
timing and strength of the northward push of warm air, and as a
result, forecast confidence is currently low for the precipitation
type Tuesday night into Wednesday.

&&

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

A broad area of high pressure sits stationary to the south of the
eastern Aleutians and Alaska Peninsula this evening. Numerical
guidance is in good agreement with the ridge remaining in place
through next week with shortwave disturbances riding up and over
the ridge through the Bering and into Southwest Alaska. Tonight, a
front moves through the eastern Aleutians and Alaska Peninsula,
producing gusty southerly winds and rain, and then weakens Monday
morning. A compact low with gale force winds in the western
Bering tracks eastward and opens into a trough Monday afternoon as
it approaches the Kuskokwim Delta coast.

Late Monday night/early Tuesday an intense warm front is forecast
to lift across the western and central Aleutians with gale to
localized storm force easterly winds. A strong southerly push
across the western and central Bering follows this front as a
surface low intensifies in the far western Bering. Rain, heavy at
times, can also be anticipated across the Aleutians as ample
moisture is drawn northward.

&&

.MARINE (Days 3 through 5/Wednesday through Friday)...

Bering/Aleutians...

There is a moderate degree of confidence overall in the 3-5 day
period. A low pressure system moving northeastward along the
Kamchatka Peninsula will make for areas of gale force
southwesterly winds across the western Bering/Aleutians on
Wednesday. There are discrepancies between guidance with respect
to how strong this low center will be, though there is a moderate
to high degree of confidence with respect to the track of this
system. Forecast confidence is moderate to high for Thursday and
Friday as winds will remain below gale force.

Gulf of Alaska...

There is a moderate to high degree of forecast confidence overall
for the 3-5 day period. Low pressure will continue to move away
from the area. The only area of uncertainty are the exact strength
of northwesterly gap winds around the Barren Islands region. As of
now, these winds are expected to at least reach gale force.

&&

.LONG TERM FORECAST (Days 4 through 7/Thursday through Sunday)...

An Omega Blocking pattern will extend across the North Pacific for
the entirety of the extended period. The ridge-axis will remain
over Southwest Alaska which will make for warmer temperatures
across the area. Southcentral will be cooler due to broadscale
northwesterly flow from being east of the ridge-axis. This will
allow for mostly sunny skies during the day and clear skies with
light winds at night as a result of strong subsidence aloft.
Moreover, clear skies and light winds will allow for cold
nighttime low temperatures across Southcentral due to radiational
cooling. The predominant low track will be across the central
Bering/Aleutians through the Bering Strait/Seward Peninsula.
During the extended period there will be chances for precipitation
across Southwest as broad southwesterly flow will allow for
moisture to enter the region. The bulk of the precipitation will
be on Saturday and Sunday. One area of lower confidence is
precipitation type as ample amounts of warmer air will move in
aloft and result in a variation of precipitation types across
Southwest. For now, the greatest chance of rain will be along
coastal areas in the Kuskokwim Delta and Bristol Bay. The best
chance for snow will be in inland locations such as the lower Kuskokwim
Valley and in the Kuskokwim and Alaska Ranges.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter 101 121 145.
MARINE...Storm 131 178.
         Gale 120 121 129 130 132 138 139 141 175 176 177.
         351 352 411 412 413.
FIRE WEATHER...NONE.

&&

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