Winter Weather Advisory 3, NWS Anchorage, AK

101 
WWAK41 PAFC 141356
WSWAER

URGENT - WINTER WEATHER MESSAGE
National Weather Service Anchorage AK
456 AM AKST Thu Jan 14 2021

AKZ131-150300-
/O.EXT.PAFC.BZ.W.0002.210115T0300Z-210115T1200Z/
Northeast Prince William Sound-
Including the cities of Valdez and Thompson Pass
456 AM AKST Thu Jan 14 2021

...BLIZZARD WARNING NOW IN EFFECT FROM 6 PM THIS EVENING TO 3 AM
AKST FRIDAY THROUGH THOMPSON PASS...

* WHAT...Blizzard conditions expected. Total snow accumulations 
  of 5 to 10 inches. Winds gusting as high as 55 mph.

* WHERE...Thompson Pass.

* WHEN...From 6 PM this evening to 3 AM AKST Friday.

* IMPACTS...Plan on slippery road conditions. Widespread blowing 
  snow will reduce visibility to one quarter mile or less at 
  times.

* ADDITIONAL DETAILS...Northeast winds will start to increase this
  morning. Limited transportable snow could be easily moved 
  around. Snow will begin to fall during the late afternoon. The 
  combination of these elements could lead to extremely poor 
  visibilities.

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.

&&

$$

AKZ125-150300-
/O.CON.PAFC.WW.Y.0003.210114T1500Z-210115T0300Z/
Western Prince William Sound-
Including the cities of Whittier, Seward, Girdwood, 
and Moose Pass
456 AM AKST Thu Jan 14 2021

...WINTER WEATHER ADVISORY REMAINS IN EFFECT UNTIL 6 PM AKST THIS
EVENING THROUGH PORTAGE VALLEY AND TURNAGAIN PASS...

* WHAT...Blowing snow expected. Visibility as low as one half mile
  at times. Total snow accumulations of 3 to 6 inches with up to 
  15 inches through Turnagain Pass. Winds gusting as high as 45 
  mph. 

* WHERE...Western Prince William Sound.

* WHEN...From 6 AM to 6 PM AKST Thursday.

* IMPACTS...Plan on slippery road conditions. Areas of blowing 
  snow will reduce visibility to one half mile or less at times. 
  The hazardous conditions could impact the morning or evening 
  commute.

* ADDITIONAL DETAILS...Winds and snowfall rates are expected to
  increase through the day. Temperatures in the lowest elevations
  should remain at or just above freezing. While this is expected
  to limit the blowing snow potential in Portage Valley, heavy 
  snow and gusty winds will continue for higher elevations through
  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.

&&

$$

http://www.weather.gov/afc

064 
WWAK41 PAFC 150015
WSWAER

URGENT - WINTER WEATHER MESSAGE
National Weather Service Anchorage AK
315 PM AKST Thu Jan 14 2021

AKZ131-151545-
/O.EXT.PAFC.BZ.W.0002.210115T0600Z-210115T1600Z/
Northeast Prince William Sound-
Including the cities of Valdez and Thompson Pass
315 PM AKST Thu Jan 14 2021

...BLIZZARD WARNING NOW IN EFFECT FROM 9 PM THIS EVENING TO 7 AM
AKST FRIDAY THROUGH THOMPSON PASS...

* WHAT...Blizzard conditions expected. Total snow accumulations of
  1 to 3 inches. Winds gusting as high as 45 mph.

* WHERE...Thompson Pass.

* WHEN...From 9 PM this evening to 7 AM AKST Friday.

* IMPACTS...Plan on slippery road conditions. Widespread blowing
  snow will reduce visibility to one quarter mile at times.

* ADDITIONAL DETAILS...Snow will initially be very light as it
  develops this evening, but will increase in intensity during the
  overnight hours through Friday morning. The worst conditions
  will likely be between 3am and 7am.

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.

&&

$$

AKZ125-150300-
/O.CON.PAFC.WW.Y.0003.000000T0000Z-210115T0300Z/
Western Prince William Sound-
Including the cities of Whittier, Seward, Girdwood, 
and Moose Pass
315 PM AKST Thu Jan 14 2021

...WINTER WEATHER ADVISORY REMAINS IN EFFECT UNTIL 6 PM AKST THIS
EVENING THROUGH TURNAGAIN PASS...

* WHAT...Blowing snow. Visibility as low as one half mile at
  times. 

* WHERE...Turnagain Pass.

* WHEN...Until 6 PM AKST this evening.

* IMPACTS...Plan on slippery road conditions. 

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
533 AM AKST Wed Jan 13 2021

.ANALYSIS AND UPPER LEVELS...

A broad upper level trough currently extends across the
Bering/Aleutians and into the Gulf of Alaska. A Rex Block
continues to persist across the western Bering Sea which is
allowing for this upper trough to remain in place at this time. An
area of low pressure is developing along a negatively tilted
trough near 42N 159W and is moving northeastward. Rapid
cyclogenesis is likely with this system due to the negative tilt
of this upper level trough. A second weak upper low is stalled out
over Bristol Bay and it is continuing to weaken as this low is
vertically stacked and is far away from the core of the jet, thus
there is little to no synoptic scale forcing to continue the
development of this low. A second low is developing near 45N 164E
and is moving eastward.

Closer to the surface, showers continue to move northwestward
across the northern Gulf into the southern Kenai Peninsula and
Prince William Sound. Snow showers continue to move northwestward
across the AKPEN and along Bristol Bay.

&&

.MODEL DISCUSSION...

Guidance is in good agreement with the placement and intensity of
synoptic scale features at both the surface and in the upper
levels, thus forecast confidence is above average.

&&

.AVIATION...
PANC...Conditions will generally remain VFR. A chance of MVFR
conditions exist before 16z as snow showers may reduce ceilings to
3000' and visibility to 6SM. There is also a chance of a Turnagain
Arm wind gusting to 20kts between 21z and 03z.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through
3/Wednesday through Friday)...

A weakening low that has been primarily responsible for the
active weather over the north Gulf coast is finally migrating west
near the AKPEN. Instability rain/snow showers continue streaming
northward across the offshore waters into Prince William Sound and
the Eastern Kenai Peninsula. The aforementioned low is bringing
another shortwave lifting northward across Southcentral this
morning, with a potential of snow over the Cook Inlet and into
the Mat-Su Valleys early today. Due to the quick nature and
limited QPF, snow accumulations are expected to only top out
around 1 inch or so. This feature combined with a trailing
shortwave will also cross the offshore waters, bringing another
round of coastal mixed rain/snow and mountain snow through today.
Persistent easterly flow across Prince William Sound into the
higher terrain will keep steady snow falling through much of that
region through the day. Avalanche concerns remain elevated. Please
check with our partners at CNFAIC.ORG for the latest.

With a relative break in the pattern late Wed into early Thu,
attention then turns to an impressive strong North Pacific low
near 42N 159W as of 3am this morning. Models are in decent
agreement showing it moving northward from the Gulf beginning on
Thursday. An associated storm force front with hurricane force gusts
and waves of 20-30 feet will move towards the north Gulf coast
on Thu. A band of colder air in the mid-levels will work into
Southcentral ahead of the precipitation with this front. This
should allow nearly all areas to start as snow. The combination of
falling snow and strong easterly winds could result in extremely
poor visibilities for locations such as Thompson Pass and Portage
Valley/Turnagain Pass. Winter Storms Watches for potential
blizzard conditions are in effect to address these concerns. The
proverbial "fly in the ointment" is some easterly flow ushering
warmer air rather quickly with this front. If this warm air were
to displace the shallow cold layer, it would cause temperatures to
rise near freezing and limit any blowing snow potential. There is
also now the chance for a triple point low to form over the
Northern Gulf and impact some of the subtleties of the forecast
as well.

The other area of interest with today's forecast is Kodiak Island.
This front will surely bring in some strong east to northeast flow
on Thu. QPF values are expected to be on the order of 1-2". There
should be enough cold air in place to allow for precipitation to
start as all snow, with even the threat of some blowing snow.
However, with warm air advection and winds coming off SSTs still
in the low 40 degree range, this will likely cause rain to mix
with the snow and limit any significant snow accumulations.

&&

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

A weakening low residing over Bristol Bay today produces some
lingering snow showers across Bristol Bay throughout today. The
rest of the Southwest Mainland should remain relatively dry
overall, with some brief periods of light snow showers possible.
No significant accumulation is expected with this. Another North
Pacific low approaches the Southern Gulf, creating strong winds
along the North Gulf Coast on Thursday which will inevitably spill
into Bristol Bay through passes within the Alaska Range. Flow will
remain gusty across the Southwest Mainland and AKPEN as it
transitions to northerly by Thursday evening as the front pushes
onshore. Any precipitation should stay confined to the Southern
AKPEN and along the upslope areas of the Alaska Range through
tomorrow night.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

Cold, northerly flow persists across the Bering, though winds have
decreased significantly to small craft or lower through Thursday
night. A longwave trough extends northwest to southeast across the
Bering and into the North Pacific, with an embedded short-lived
polar low tracking across the Western Bering. Snow showers are
expected to linger along the Eastern Aleutians and Southern AKPEN
through tonight before becoming confined to the Southern AKPEN on
Thursday as a new system approaches. A strong North Pacific low
pushes towards the Southern Gulf on Thursday. A brief period of
storms are likely on Thursday south of the AKPEN with this as
well. Otherwise, expect relatively calmer seas and winds overall.
The next storm system of concern looks to approach the Southern
AKPEN late Friday into Saturday, which could bring another round
of showery precipitation to both the Bering and the Aleutian
Chain, as well as some high winds and waves.

&&

.MARINE (Days 3 through 5 - Fri through Sun)...

Gulf of Alaska: Model tracks and development vary considerably,
so forecast confidence is low. A North Pacific low moves over
Kodiak Island into the Alaska Peninsula through Sun. Lingering
northeast small craft winds and waves continue through Cook Inlet
and the Shelikof Strait, diminishing Fri night. A barrier jet
remains along the North Gulf Coast through Sun. East small craft
winds with gale force gusts continues. After the low passes
Kodiak, southerly small craft winds spread over the Southeast Gulf
diminishing Sun. Wave heights to 21 feet remain through Sun.

Aleutians / Bering: Model tracks and development vary somewhat,
but forecast confidence is good. The Southwest Alaska low
dissipates Sun. Widespread northerly small craft winds and waves
move over the Eastern Bering, diminishing late Sat. High pressure
over the Western Aleutians and Bering yields to a trough out of
Siberia. Westerly small craft winds spread into the Central Bering
through Sun. Wave heights to 17 feet south of the Aleutians and
Alaska Peninsula through Sun.

&&

.LONG TERM FORECAST (Days 3 through 7: Friday through Tuesday)...

A pattern change is expected to take place on Friday as the North
American Ridge builds poleward while a trough remains in place
over the Bering Sea. This change in the jet position will bring
storms from the north Pacific into the Alaska mainland, leading to
a more active weather pattern for Southcentral. Due to the
ridging, temperatures aloft are expected to remain on the warmer
side, so rain is possible for coastal locations with heavy and
persistent snow for the higher elevations. In this pattern the
track of individual lows will determine whether or not
precipitation will make it into the population centers of
Southcentral. The GEFS ensemble means places the low track over
the AKPen, which would result in a similar pattern over the
southern mainland as observed this week with precipitation
favoring the coast and downsloping dominating the population
centers. However, with the shift in the jet stream, upper level
flow is more likely to take on a southwest orientation as
shortwave troughs lift out of the area, which is a favorable
pattern for precipitation from Anchorage into the Mat-Su Valleys.
The ECMWF ensemble means place the low track farther to the east,
favoring the track of the Prince William Sound low, which could
also result in snow or rain for the population centers. With the
broad southerly flow temperatures are expected to remain well
above average through the forecast period.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Storm Watch 125 131.
MARINE...Heavy Freezing Spray Warning 180 185 414.
Storm Warning 119 120 130 131 132 138 139 150 351 352.
Gale Warning 127 136 137 155 160.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...ED
SOUTHCENTRAL ALASKA...MF/MO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KM
MARINE/LONG TERM...MK/CJ