Blizzard Watch 6, NWS Anchorage, AK

850 
WWAK41 PAFC 231838
WSWAER

URGENT - WINTER WEATHER MESSAGE
NATIONAL WEATHER SERVICE ANCHORAGE AK
938 AM AKST FRI DEC 23 2016

AKZ125-240745-
/O.UPG.PAFC.BZ.A.0006.161225T0000Z-161225T1500Z/
/O.NEW.PAFC.WW.Y.0017.161225T0000Z-161225T1800Z/
WESTERN PRINCE WILLIAM SOUND-
INCLUDING THE CITIES OF...WHITTIER...SEWARD...GIRDWOOD...
MOOSE PASS
938 AM AKST FRI DEC 23 2016

...WINTER WEATHER ADVISORY FOR SNOW AND BLOWING SNOW IN EFFECT
FROM 3 PM SATURDAY TO 9 AM AKST SUNDAY FOR TURNAGAIN PASS AND
PORTAGE VALLEY...

THE NATIONAL WEATHER SERVICE IN ANCHORAGE HAS ISSUED A WINTER
WEATHER ADVISORY FOR SNOW AND BLOWING SNOW...WHICH IS IN EFFECT
FROM 3 PM SATURDAY TO 9 AM AKST SUNDAY. THE BLIZZARD WATCH IS NO
LONGER IN EFFECT.

* LOCATION...TURNAGAIN PASS AND PORTAGE VALLEY.

* SNOW...6 TO 12 INCHES. HIGHEST AMOUNTS WILL BE AT HIGHER
  ELEVATIONS.

* VISIBILITY...QUARTER MILE POSSIBLE.

* WIND...EAST WINDS 30 TO 50 MPH.

* TIMING...SNOW WILL INTENSIFY LATE SATURDAY AFTERNOON BECOMING
  HEAVY AT TIMES BY EVENING...IMPROVING SUNDAY MORNING. BLOWING
  SNOW WILL DIMINISH VISIBILITIES DOWN TO ONE HALF MILE OR LESS AT
  TIMES THROUGH PORTAGE VALLEY SATURDAY EVENING AND AREAS OF
  TURNAGAIN PASS THROUGH SUNDAY MORNING.

* IMPACTS...SNOWFALL COMBINED WITH STRONG WINDS AND BLOWING SNOW
  MAY PRODUCE NEAR WHITE-OUT CONDITIONS AT TIMES. SNOW MAY MIX
  WITH OR CHANGE TO RAIN CREATING ICY CONDITIONS. DRIVING MAY
  BECOME VERY DIFFICULT.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A WINTER WEATHER ADVISORY FOR SNOW AND BLOWING SNOW MEANS THAT
VISIBILITIES WILL BE LIMITED DUE TO A COMBINATION OF FALLING AND
BLOWING SNOW. USE CAUTION WHEN TRAVELING.

&&

$$

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
434 PM AKST Thu Dec 22 2016

.ANALYSIS AND UPPER LEVELS...
Currently the mainland remains under the influence of an upper
level longwave trough, with one low far to the north over the
Arctic Ocean, and a second low over the Gulf of Alaska. To the
west, a ridge is building over the eastern Bering Sea/Alaskan west
coast. An upper level shortwave is moving through the pattern,
bringing some snow showers to the Pribilof Islands last night and
somewhat gusty southerly flow to the Kuskokwim Delta this morning.
This shortwave is weakening as it moves through the ridge and is
not anticipated to have major impacts as it moves onshore.

To the east, the low in the Gulf of Alaska is well stacked and
reflected in a weakening surface low. Satellite imagery shows
classic cold air advection signature on the backside of the low.
A tightening gradient as the ridge builds in from the west is
causing gusty outflow winds in the usual north/south facing gaps
and passes. A weakening surface trough associated with this low
is bringing snow showers to the Copper River Basin this morning.

&&

.MODEL DISCUSSION...
Models are in good agreement on the current forecast. NAM/GFS
blend was used, mainly to pick up higher resolution details on
the wind in both the east and the west.

&&

.AVIATION...
PANC...With the ridge moving in overhead, the potential for fog
exists again tonight. Areas of fog have lingered in Knik Arm for
much of today, so it could drift southward to the airport at anytime.
There should be some improvement in the area early Friday morning
as some mid and high clouds pass through, but localized areas of
fog will likely remain in the area. Conditions should improve
for good by later tomorrow as flow increases out ahead of the
next storm system in the Bering Sea.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Outflow winds have been going strong and will continue through
much of Friday with low pressure in the Gulf and ridging building
in from the west. As the first ridge diminishes this evening then
another, stronger, ridge will take its place from the west. The
ridge axis will move through Southcentral Alaska Friday
afternoon/evening and will coincide with weakening outflow winds.
While the winds do stay strong, blowing snow conditions are
possible through Thompson Pass. The ridging is also conducive to
fog formation and fog is expected around the Cook Inlet area again
tonight.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2...Fri and Sat)...
The next in the series of the weak fronts is moving into the YK-
Delta this evening. This should bring another round of light snow
with minimal accumulations to areas from the coast to Aniak.
Behind this front, winds will shift to westerly and help to usher
in some low-level moisture. This coupled with a ridge building
over the area tonight could spell widespread fog Fri morning for
much of the area. The fog should not be able to last through the
day as flow switches to a more northeasterly offshore direction in
response to the next Bering front. This front will bring snow to
the coast by late Fri evening. Gusty south to southeast winds will
accompany this front, which could lead to some blowing snow
potential along Delta coastline. This should be rather limited
though with warm air advection and synoptic southeasterly winds.
Enough warm air does move inland by Saturday that the snow will
likely switch over to at least a mix, if not all rain.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2...Fri and
Sat)...
A storm-force low is approaching the central Aleutians from the
North Pacific. This low will "stir-up" the pattern as it brings a
a hefty swath of warm air up into the Bering. This warm air will
cause the precipitation that accompanies the system to switch from
snow quickly over to rain for most of the islands. With modest
mid-level support, it does look like gusts will reach into the 60
mph range. These should reach Dutch by late tomorrow morning and
then stretch toward Nelson Lagoon by Fri evening. This low will
then move into the central Bering early Sat where it will slowly
weaken. Another slightly stronger low will move towards the
Western Aleutians by late Fri. This low should track slightly
further south and keep the strongest winds south of our marine
areas.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The day 3 forecast begins on Saturday evening with a front draped
from the southwestern mainland into the Gulf. The gale-force front
will bring snow to the north Gulf coast on Sunday while the Cook
Inlet region remains downsloped and dry. Western Prince William
Sound will take the brunt of this system. The same front will be
weakening over the southwest, leaving scattered rain and snow
showers in the area. The responsible low pressure system will
encompass most of the Bering, but will have little in the way of
forcing for widespread precipitation. Look for scattered to
numerous showers across the area.

The extended forecast begins late Sunday with the same pattern.
A broad trough sits over the Bering with the jet stream to the
south of the Aleutians. The previous front will hang along the
north Gulf coast, then fall apart while the trough gradually
shifts eastward. Toward the middle of next week, a pattern change
is underway as a developing Kamchatka low looks to amplify the
pattern over the western Bering. This will bring ridging, a front,
and warmer air to the Bering, while the Southcentral will remain
in a weak outflow pattern with clear skies, light winds, and
enhanced gap winds along the coast.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Heavy Freezing Spray Warning 129.
         Storm Warning 172 181.
         Gale Warning 130 132 150 155 160 165 170 171 173
                      174 175 176 179 180 181 185.

&&

SYNOPSIS AND MODEL DISCUSSION...LF
SOUTHCENTRAL ALASKA...DK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MO
LONG TERM...MTL