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000
FXAK69 PAFG 230038
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
338 PM AKST Wed Feb 22 2017

.DISCUSSION...

Models...Good agreement through Monday, then some divergence in
the handling of the building ridge over the Bering Sea next week.
The GFS is more aggressive and has done marginally better over
the last few days so will lean a bit more in that direction for
now. Surface initialized well against the 22/18Z analysis. For the
short term will go with an even blend of the model outputs.

Aloft...At 500 hpa...Shortwave moving through the interior now
will continue east through the evening. A ridge over the west
coast will continue to build and slide east with the axis lying
from Wainwright to Tanana to Seward by Thursday morning with 528
dam heights extending north over the arctic coast. By Thursday
evening the ridge axis will rotate east to lie from Demarcation
point to Cordova with 540 dam or greater heights over the
southeast half of the mainland. A 488 dam closed low over the
western Aleutians today will move over the Gulf of Anadyr by
Friday morning as an open wave with a trough extending southeast
over Nunivak Island then southwest over Unimak Island. As the
ridge continues to rotate flow becomes zonal over the state and
will allow a series of shortwaves to rapidly move across the area
through the weekend. The trough over the eastern Bering Sea will
help flatten the ridge as it moves inland to the Western Interior
on Friday afternoon, and to the Eastern Interior by Friday night.
A 500 dam low will develop late Friday over the eastern Kuril
Islands and move just west of the Gulf of Anadyr by Saturday
morning. At 850 hpa...-20 isotherm lies from Old Crow YT to
Allakaket to Deering and will move north to lie north of the state
by Thursday afternoon. The zero will nose in over the lower Yukon
Delta Thursday morning, then slide east over the western Alaska
Range Thursday evening through Friday morning.

Surface...A 1023 mb low over the Beaufort Sea will move east. Weak
ridging with a 1029 mb center will continue to build over the
arctic plain and central arctic coast, with a 1041 mb high over
the western arctic. The high center will persist over the western
arctic as the ridge axis moves east across the arctic and arctic
coast to MacKenzie Bay by Thursday afternoon and to Banks Island
by Thursday evening. A 1042 mb center will develop in the ridge
over the upper Yukon Flats by Thursday morning then move into
Canada. A leeside trough will develop tonight over the arctic
plain as the ridge slides east. The leeside trough north of the
Alaska Range will weaken a bit this evening then become more
enhanced Thursday. Southwest flow will develop from Fairbanks west
as ridging over the northeast Pacific and Gulf of Alaska persists
through the weekend.

Arctic Coast and Brooks Range...Short term some stratus over the
central and northwest coast with some flurries. To the east mainly
clear and cold through the night. Weather system moving into
the area from the southwest will bring increasing clouds and snow
to the area by Thursday afternoon over the northwest coast and
spreading east. Winds coming up rather smartly over the northwest
coast so will be issuing a Winter Weather Advisory for the area
due mainly to blowing snow. As the front progresses east the winds
will pick up so may need to look at blowing snow issues in other
areas tonight and tomorrow. Temperatures on the increase as the
system moves in, so wind chill issues will be ending even as the
winds increase.

West Coast and Western Interior...Several waves of weather moving
through the area will spread more snow to the area, along with a
chance of freezing rain to the lower Yukon Delta and upper
Kuskokwim River Valley. Winds are increasing in the Bering Strait
and on St Lawrence Island and that will continue through the
evening with snow spreading into the area and Blizzard conditions
developing. No changes to the current suite of Warnings and
Advisories, will however be making some changes to the other
Watches currently in effect. Zone 210 will be downgraded to an
Advisory, while the remainder of the Watches will be upgraded to
Winter Storm or Blizzard Warnings. Another front moving in
Thursday late will bring another round of warnings and advisories
for Friday. Stay tuned.

Central and Eastern Interior...2 to 4 inches of snow tonight
across the area with taper off toward morning with some clearing
Thursday. More Snow Thursday night and Friday with 2 to 5 inches
possible. Then the big snow expected on Saturday into Sunday with
3 to 8 inches possible. Winds generally light with the exception
of the Alaska Range passes where it will be gusty to around 50 mph
at times. Temperatures warming so a slight chance of some freezing
rain in the Alaska Range.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...

Wind Chill Advisory for AKZ203-AKZ204.

Winter Storm Warning for AKZ208-AKZ217.

Wind Advisory for AKZ226.

Blizzard Warning for AKZ201-AKZ207-AKZ209-AKZ213.

Winter Weather Advisory for AKZ210-AKZ211-AKZ212-AKZ214-AKZ216-
AKZ218-AKZ219.

Gale Warning for PKZ200-PKZ210-PKZ215-PKZ220-PKZ225-PKZ230.

Brisk Wind Advisory for PKZ235.

&&

$$

SDB FEB 17


000
FXAK68 PAFC 231404
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
504 AM AKST Thu Feb 23 2017

.ANALYSIS AND UPPER LEVELS...
The pattern is divided into two parts this morning. Over the west,
a fairly deep trough with a closed upper level low resides over
the Bering. Meanwhile, in the east, a ridge of high pressure is
building over the central mainland. The most active weather is in
between these two systems as a 145 kt jet ferries potent warm air
northward. The first warm front has already made its way up to the
Seward Peninsula. The trailing quasi-cold front is blasting
through the Alaska Peninsula stretching up towards Nunivak Island.
Most of the precipitation associated with this feature has been
rain so far, but there is colder on the backside of it which could
allow things to change back to snow. Over the Western Bering, the
parent low is quickly filling as it slings some snow showers and
storm-force gusts through the Aleutian chain.

In the east, drier and warmer is the rule under the building
ridge. Winds are relatively calm at all locations. The biggest
forecast challenge will be abundant low stratus and perhaps some
patchy fog.

&&

.MODEL DISCUSSION...
All models remain in good synoptic agreement. This is lending to
moderate forecast confidence in the big picture items. The GFS was
preferred out west for continuity. The NAM was preferred in the
east for better resolution. The remaining areas of uncertainty are
the longevity of the low stratus around the Cook Inlet today and
then the precipitation type on Friday. Models seem to be trending
towards a slightly colder scenario for Friday`s front. However,
Turnagain Arm winds and the depth of the warm air could lead to a
messy mix of precipitation. This portion of the forecast was left
mostly unchanged for this package.

&&

.AVIATION...
PANC...MVFR conditions due to low stratus will persist at least
through the morning hours. With very little change to the pattern,
this stratus could last until after midnight Thu night. However,
thinking is still that as some drier air works in today, it should
be able to mix out some. The next round of precipitation will move
in late tonight bringing MVFR ceilings. Precipitation is likely
to start as a mix of rain and snow. If it is more snow than rain,
expect visibilities to drop as well.

&&

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

Temperatures across Southcentral Alaska will be warming up a bit
today as the warm core ridge moves over the area. There are some
clouds riding over the ridge but there does not appear to be any
precipitation with any of these impulses. That will change
overnight into Friday as a front moves through the area from the
west.

Tomorrow poses a challenge as to the type of precipitation that
will occur in the Cook Inlet area. While temperatures will be warm
overnight, they main batch of precipitation will come as the
colder air moves in which could mean a mixed bag of precip types
throughout the day. There is a chance for some brief freezing rain
Friday morning near Anchorage southward to Kenai as the system
moves in, but this is looking less likely. What looks most likely
is for a rain snow mix in the late morning to mid afternoon and
then have all precipitation turn to snow by late afternoon.
However precipitation will probably not last for long after it
turns to all snow.

There is a chance that the vast majority of the precipitation
will be snow with just a little rain mixed in, but the south to
southeast winds before the precipitation arrives will probably be
enough to push temperatures high enough above freezing for some
rain. However it is interesting to note that both the GFS and NAM
MOS data show all snow for Anchorage, Kenai, and points northward
for the entire event in spite of temperatures around 40.
Regardless of what happens, it will likely make for some periods
of difficult travel conditions around the region. An SPS has been
issued to address this.

&&

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

A system extending from near Hawaii will continue to spread warm
moist air across southwest AK today and tonight. Temperatures
will rise above freezing today except for portions of the lower
Kuskokwim Valley. Although some snow will persist this morning
near Hooper Bay, precipitation will change to rain along the coast
and well inland. As the front progresses inland tonight,
temperatures will drop to freezing or below and rain will change
to snow as the main band of precipitation moves east.

Partial clearing from the west Fri morning will allow some fog
formation, as snow reaches the Alaska and Aleutian ranges during
the afternoon and overnight. Beginning on Sat the next warm front
spreads a mix of snow and rain across the region through Sun.

&&

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

The initial stream of tropical moisture will continue to spread
rain over the eastern Aleutians today before moving inland. Cooler
air over the western Aleutians with snow showers will spread east
tonight before moving away from land. The next gale and storm
force warm front will approach the western Aleutians tonight with
snow changing to rain. This rain will then proceed across the
chain through the weekend.


&&

.LONG TERM FORECAST (Days 3 through 7)...
The active weather pattern over the Bering Sea will begin to move
into the Mainland this weekend as high pressure slides southward
into the North Pacific. This will allow for a gale force front
over the Bering Sea to spread gusty winds and rain/snow into the
Southwest Mainland with deep onshore flow for much of the weekend.
Then by early next week the models continue to be in good
agreement that an arctic trough will deepen over the Mainland Mon-
Tue, ushering in colder air and gusty offshore flow to much of the
Gulf Coast. What is still unclear however is the exact track that
this trough will take through the Mainland, which is having a
significant impact in the possibility of snow to the South
Mainland into the middle of next week. The EC and GEM are more
aggressive in bringing Bering Sea moisture into the Mainland ahead
of the arctic trough, and a result are more aggressive in the
potential for a snow event Mon-Tue. The GFS on the other hand has
been very consistently more aggressive in bringing cold/dry
interior air, leaving most of the South Mainland dry into the
middle of next week. For now the forecast favors the drier GFS
solution as it has been much more consistent. Forecast confidence
is below average.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Storm warning 177 178.
Gale warning 155 165 170 172 173 175 176 180 185.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...MSO
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DS
LONG TERM...DEK


000
FXAK67 PAJK 231432
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
532 AM AKST Thu Feb 23 2017

.SHORT TERM...A weak system in the eastern Gulf of Alaska
resulted in a thick dusting of snow, around a half inch or less
over the Juneau area last night, and probably Skagway, Gustavus,
Hoonah, Tenakee, Angoon, and Sitka as well. If one could describe
the bands of very light snow ever as "intense," one could say the
heaviest period occurred late yesterday evening. The line
separating cloudy from clear skies lies across the Icy
Strait/Point Retreat corridor as of 4 AM. We fully expect that as
a deformation slides south and east, that this line will erode
more and more from the north through the day. Likewise, flurries
in Juneau and Angoon will end soon. Some fog briefly occurred at
Gustavus as the stratus dissipated, and repeat scenarios may occur
briefly this morning, across other communities that received
fresh snow overnight, but we do not think this will be impactful.
Therefore we omitted even patchy fog.

From Petersburg south, communities have experienced a mix of
clouds and clear skies, but generally more hit or miss than the
steady organized clouds of the north. As the deformation band
passes over this region this morning, we still think there is a
slight of light snow across Prince of Wales Island, Ketchikan, and
Metlakatla this morning. But any possibility of snow moves east by
18Z. Any snow will that does fall will hardly amount to a dusting.

A ridge aloft steadily builds over the Gulf and into the Panhandle
through tonight. This induces a stronger inverted trough at the
surface through the southern Panhandle. Thus northwesterlies
offshore will strengthen to 25 kt tonight. Likewise Stephens
Passage and potentially Clarence Strait will experience increases
as well. The building surface ridge also will swell seas to 8 to
9 feet later today into tonight across the eastern gulf.

Models indicate some mid to high level cloudiness dropping south
across the northern Panhandle this afternoon and tonight, but we
are not convinced that skies will be opaque. We mainly represent
skies as partly cloudy through the period.

NAM products were used as guidance where adjustments were made,
but few were needed.

.LONG TERM...Strong upper level ridge over the western gulf will
persist into early next week producing mainly north or
northwesterly flow over the panhandle. The result of which is a
rather dry and quiet forecast for the most part with one
exception. That exception is the moderate strength trough that
will be moving through the ridge Fri night into early Sat.

Long range models are getting better at fleshing that trough out.
The issues on strength of the system that were apparent between
forecast models 24 hours ago has settled out with a consensus
resting somewhere in the middle of the range at around 1016 mb.
Progression of the system through the area has also trended
toward faster with the trough taking most of the precip out of the
area by late Sat afternoon. All in all, This trough is looking
like it will be a quick hitter with enough cold air around that
the central and northern inner channels at least will see some
snow out of it. Outer coast and southern panhandle will be a
little more tricky for ptype due to temps expected in the mid to
upper 30s at times in those areas so primarily went with a mix.
Snow accumulations are expected to be up to 2 inches for the most
part where it does snow.

Pattern change in the works for mid next week as the upstream
ridge gets suppressed by a strong shot of cold air from Siberia.
The developing cold trough looks to tilt in a positive direction
toward late week orientated its axis just to our NW with a
embedded upper low lodged somewhere in the western half of the
gulf, though the exact structure has been shifting for the last
few days. The overall trend is a return to onshore flow for most
of the area with some precip possible for mid next week and
beyond.



&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ041-042.
Small Craft Advisory due to Seas for PKZ043.
&&

$$

JWA/EAL

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