Winter Storm Watch 1, NWS Anchorage, AK

809 
WWAK41 PAFC 131924
WSWAER

URGENT - WINTER WEATHER MESSAGE
National Weather Service Anchorage AK
1024 AM AKST Wed Jan 13 2021

AKZ131-141500-
/O.UPG.PAFC.WS.A.0001.210114T1800Z-210115T1500Z/
/O.NEW.PAFC.BZ.W.0002.210114T1800Z-210115T1500Z/
Northeast Prince William Sound-
Including the cities of Valdez and Thompson Pass
1024 AM AKST Wed Jan 13 2021

...BLIZZARD WARNING IN EFFECT FROM 9 AM THURSDAY TO 6 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 9 AM Thursday to 6 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
  markedly Thursday morning. Any transportable snow could be
  easily moved around. Snow will begin to fall during the
  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.

&&

$$

AKZ125-141500-
/O.UPG.PAFC.WS.A.0001.210114T1800Z-210115T0200Z/
/O.NEW.PAFC.WW.Y.0003.210114T1500Z-210115T0300Z/
Western Prince William Sound-
Including the cities of Whittier, Seward, Girdwood, 
and Moose Pass
1024 AM AKST Wed Jan 13 2021

...WINTER WEATHER ADVISORY IN EFFECT FROM 6 AM TO 6 PM AKST
THURSDAY THROUGH PORTAGE VALLEY AND TURNAGAIN PASS...

* WHAT...Snow expected. Total snow accumulations of 4 to 8 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 will start to increase early Thursday
  morning as snowfall rates increase. Temperatures will warm 
  slowly above freezing during the afternoon. While this is 
  expected to limit the blowing snow potential in Portage Valley, 
  heavy snow and gusty winds will continue for higher elevations 
  through Thursday 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

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
553 PM AKST Tue Jan 12 2021

.ANALYSIS AND UPPER LEVELS...
The pattern over Southern Alaska is very similar to yesterday with
a surface low just west of Kodiak Island and a decaying front in
the Eastern Bering Sea continuing to bring snow to the Eastern
Aleutians and Pribilof Islands. Most of mainland Southern Alaska
is under weak easterly flow aloft, but it is enough to keep most
of the leeside of the mountain ranges dry with the showers
remaining on the windward side and over the mountains.

The 250 mb jet stream is well south of us and where the real
action is beginning. There is a trough in the jet stream, and
where this inflection point is a low is rapidly intensifying near
40N 165W. This can be seen on GOES17 satellite and this system
will be the one that moves into the Gulf of Alaska on Thursday.

&&

.MODEL DISCUSSION...
Models remain in good overall agreement over the next few days.
The strong low moving into the Gulf late Thursday will be complex
and models still are not sure where the individual lows will be.
The frontal boundary location is in good agreement between models
which is the most important aspect of the forecast. The secondary
centers become important when one rotates along the front, as it
can enhance the winds there so we will be watching for this the
next few model runs. Also of note is a small but potentially strong
low in the northwest Bering Sea Thursday into Friday. The location
and size of this feature shows it may be another one of these small
but intense polar lows we have been seeing lately. Models are
detecting it but don't seem to know quite what to do with it yet.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. There will be
some periods where there will be showers nearby, but they are
expected to continue to occur mainly over the Chugach Mountains
keeping VFR conditions at the airfield.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through
3/Tuesday through Thursday)...

An sprawling and weakening low continues to slowly fill and drift
north with the low pressure center remaining near Kodiak Island
this evening. This low continues to harbor a multitude of smaller
waves embedded in the larger scale circulation. One such feature
led to a quick-hitting round of snow over Anchorage earlier today
with 0.5-1.5 inches dropped as the fast moving band and associated
inverted trough raced northwest. Additional small waves of energy
will continue to drive rain and snow showers into the Gulf Coast
as the low lifts north into Southwest AK and becomes a remnant
open wave by Wed.

After several days of a very stagnated weather pattern, a major
shift in the synoptic setup will begin as the stubborn low
departs on Wed. As low-mid level winds becomes briefly more
southerly, another quick round of snow will move up the Cook Inlet
and into the Mat-Su Valleys with a push of colder air and the
passage of one final southerly shortwave. Around a dusting to 1/2
inch is possible for the Anchorage Bowl late Wed morning with a
few inches possible in the Western Susitna and near Hatcher Pass
later into Wed evening and overnight. Around 4-6 inches of snow is
also expected in the Seward area in association with the same
wave passage very early Wed morning.

Attention then quickly shifts to the deep low moving into the
Gulf on Thurs and Fri, with a number of hazards possible for both
marine and land areas across Southcentral. Winds ahead of the
front are expected to increase well into storm force range with
gusts to hurricane force possible as the front progresses north on
Thursday, with winds then quickly decreasing from south to north
as the front reaches the Northern Gulf Coast late Fri evening.
Some uncertainty remains with the evolution and timing of this
system, and some solutions hint at a triple-point low forming
along the front in the Eastern Gulf by Thurs evening. Main
concerns over land will involve strong outflow winds and
blowing/falling snow potential ahead of the frontal approach in
Thompson Pass from late Thurs into early Fri. On a similar note,
gap winds through Portage Valley and Turnagain Pass may combine
with falling snow on Thurs night to create significant blowing
snow and visibility reductions. Stay tuned for additional forecast
updates and potential weather headlines for this event towards
the end of the week.

&&

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

A weakening surface low over the Alaska Peninsula will allow for
snow showers to remain across interior Bristol Bay, while the
Kuskokwim Delta and Valley remain dry through late Wednesday.
Southwest Alaska will see a brief period of quiet weather early
Thursday morning into the afternoon hours before the next system
approaches the region. A North Pacific low lifting northward will
bring strong storm force winds south of the Alaska Peninsula and
allow for gusty conditions across interior locations of Bristol
Bay as well. Chances for precipitation will also increase on
Thursday through the end of the week across these regions. The
dominant precipitation type will remain as snow, but warmer
temperatures moving in with this low system could allow for a mix
of rain and snow for some of the southern locations across Bristol
Bay and the Alaska Peninsula.

&&

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

The persistent, cold northerly flow pattern that has dominated
the Bering and Aleutians over the past few days will begin to
weaken tonight into Wednesday. This will allow for the blowing
snow conditions to diminish, with the advisory for Dutch Harbor to
improve throughout the evening. However, widespread snow showers
will continue across the region through Wednesday night before
tapering off. Heavy freezing spray will also be a concern over the
Northern Bering through tomorrow before the winds begin to
weaken. Conditions become much quieter once the northerly flow
pattern weakens.

Over the Western Bering, a compact low moves near Shemya this
afternoon, then weakens by Wednesday afternoon. Models are
struggling with another complex low entering the Western Bering
on Thursday. However, these systems shouldn't have any widespread
impacts. A more impactful system moves near the Eastern Aleutians
and Alaska Peninsula on Thursday morning, which will bring a brief
period of storm force winds by the afternoon. This system will
then track into the Gulf early Friday before another strong North
Pacific system approaches the eastern Aleutians Friday afternoon.

&&

.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 Weather Advisory: 185.
MARINE...Storms: 352.
         Gales: 132, 150, 178, 351.
         Heavy Freezing Spray: 180, 185, 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...AS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...MK/CJ