Heavy Freezing Spray Warning 77, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
441 PM AKST Mon Nov 28 2016

.ANALYSIS AND UPPER LEVELS...
The upper level pattern shows a low centered just a little bit
north of Barrow with a trough extending out of it to the south
across the western part of Alaska, over the Alaska Peninsula, and
into the North Pacific.
At the surface there is a large low south of Kodiak Island which
is in a good location relative to the jet stream to keep
intensifying over the next 18 to 24 hours as it tracks to the
northeast. Another low is just north of the Alaska Peninsula which
is easily seen on satellite with convective bands rotating around
it. The offshore pressure gradient over most of southern Alaska
is increasing and that will be the case for the next few days.

&&

.MODEL DISCUSSION...
Models are handling the synoptic scale features well over the next
few days. The largest synoptic difference creeps up around
Thursday in the Gulf of Alaska area where the GFS and ECMWF are
playing the low a bit differently with the GFS consolidating it
into a stronger low that is farther north. The ECMWF is a broader
low with the center weaker and a bit farther south. This
difference will have an impact of the winds and precipitation
along the north Gulf coast as well as possibly farther inland in
Southcentral Alaska. Another feature that is more subtle but will
have a difference in the forecast in the Cook Inlet and Mat-Su
valleys is on Wednesday with a baroclinic zone that will be
moving south to north over the region. The GFS and ECMWF both have
this zone farther west over the Alaska Range and that solution
will keep most of the snowfall over there should they verify. The
NAM is tracking it over Anchorage and the Matanuska valley. This
solution would bring snowfall to those areas on Wednesday. At this
time the farther westward solution looks more likely which will
keep Anchorage and the Matanuska valley dry, but it is worth
watching.

&&

.AVIATION...
PANC...VFR conditions and light winds are expected to persist. The
one wild card is the potential for stratus to move into the area.
There is a stratus deck around the 2500 to 3500 ft level north of
the area that could sneak into the area around PANC. At this time
it looks like it will remain no worse than SCT coverage, but it is
possible that it could go BKN.

&&

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

Forecast remains on track as a surface low is in the process of
rapidly deepening in the Gulf of Alaska. This surface low will
track toward the ALCAN Tuesday and Tuesday night, but the
deformation zone aloft will spread snow through the entire Copper
basin and into Valdez and Thompson Pass. A very strong offshore
pressure gradient will accompany the 960-965 hpa low. Accompanied
with strong cold air advection, all coastal wind gaps will
rapidly increase tomorrow, especially Whittier and Thompson Pass
as both will reach near hurricane force. This will result in snow
and blowing snow conditions with near whiteout conditions through
Thompson Pass. In the Copper Basin, snowfall accumulations will
be mostly light with more moderate accumulations in the extreme
eastern portion of the Copper Basin. Cold air dropping south
through Broad Pass in the Susitna Valley will support very cold
wind chills -30 to -45 F.

The strong low will quickly move into Canada Wednesday morning
before another fast moving low tracks into the Gulf Wednesday
afternoon, spreading rain and snow showers to the coast...and snow
chances inland by Wednesday evening.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A ridge across the northwest strongly influences weather
conditions to trend colder and drier across the Southwest through
midweek. Low pressure across the Bering keeps a tighter pressure
gradient along the Kuskokwim Delta which will increase northeast
winds. A wind chill advisory was issued with the afternoon package
as colder temperatures settle in tonight and gusty winds prevail
through early Thursday. A surface low moving across the Aleutians
on Tuesday night forces a stronger gradient across the Kuskokwim
Delta bringing the coldest wind chills through Wednesday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The low over the eastern Bering moves a front across the Alaska
Peninsula tonight on its track to the southeast. The next system
moves a front across the western and central Aleutians tonight
then across to the Alaska Peninsula late Tuesday. The front should
make northern progress to the central Bering by tomorrow afternoon
with a mix of rain and snow developing along the boundary. The
Pribilof Islands should see light snow, with areas of blowing snow
Tuesday night as the low center passes to the eastern Aleutians.
Strong northeasterly flow increases behind the front across much
of the Bering along with increased chances for snow as a shortwave
dives across the northern Bering late Wednesday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The run to run evolution of both the ensemble and deterministic
models continues through much of the long-term forecast, and have
yet to settle on a common solution with regard to some key
synoptic features. The low entering the Gulf Thursday, and the
system tracking through the Bering Friday and into early next week
remain the primary focus in this time-frame. An area of low
pressure will skirt the Aleutian Islands Thursday and move into
the Gulf of Alaska on Friday. That is where the models continue to
struggle with the track and strength of the low. Yesterday, models
progged this area of low pressure to move across the northern Gulf
over Kodiak Island and near Prince William Sound which would have
brought a very decent shot of snowfall across much of Southcentral
Alaska. However, models now prog this low further south and east
in the Gulf of Alaska which could potentially keep a good bit of
the moisture further south instead of pushing it inland. At the
same time, a brief warm up was expected with the track of the low
pressure system but now it appears that this will not be the case
as the more southern track will likely keep a tap of colder and
drier arctic air over Southwest and Southcentral Alaska.

The take-away message is that snow chances for interior portions
of Southcentral and Southwest Alaska continue to look quite
disappointing as the synoptic features are tracking just a little
too far north or a little too far south. However, precipitation
chances along the Northern Gulf coast and Prince William Sound
still look promising with these incoming systems. Some of the
coldest temperatures are expected by the weekend with the
potential for single digit high temperatures over west Anchorage Sunday.
There is still the potential for snow across Southwest and
Southcentral Alaska as models fluctuate, so it's something worth
watching.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning...131.
         Wind Chill Advisories...145 155.
MARINE...Storms...351 352 178.
		Gales...119 120 121 127 129 130 131 132 411-414 165 170 172-177
				179 180 185.
		Heavy Freezing Spray...121 160 180 181.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...JA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KH
LONG TERM...TP