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000
FXAK69 PAFG 291302
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
502 AM AKDT Wed Mar 29 2017

.SYNOPSIS...
Aloft...
A long wave trough over mainland Alaska will retrograde to the
West Coast of Alaska and Eastern Bering Sea by Thu then remain
there through the weekend into next week. The long wave ridge over
NW Canada will build into Eastern Alaska on the weekend and
persist into next week. This pattern change is setting up
Northern Alaska for a much warmer and more active weather pattern
as flow aloft turns southerly and increases from Thu into the
weekend.

Several short wave troughs will drop from north of the Russian
coast over the West Coast of Alaska and into the long wave
trough over the next few days. The first trough will move south
over the Chukchi Sea today and to the Yukon Delta Thu. There will
be patchy clouds and flurries with this. The main affect will be
north winds gusting to 25 mph with areas of blowing snow along the
trough. A second trough will move to the northern Chukchi sea Thu
pm and to the Western Arctic Coast to Bering Strait by Fri am.
Will see more clouds and flurries with this feature...and north
winds gusting 25 mph with areas of blowing snow.

A series of short wave troughs will make their way north over
Interior Alaska over the next several days bringing snow or a
chance of snow with each feature along with periods of southerly
Chinook winds near the Alaska Range.

The first trough moving north is now over the eastern Brooks Range
and will move north of the Arctic Coast this afternoon. Snow will
taper off to flurries as it moves north of the Brooks Range.

The second trough moving north is in the Gulf of Alaska and will
move north over the Alaska Range by 4am Thu...to Huslia to Old
Crow by 4pm Thu...to Ambler to Barter island by 4am Fri and then
elongating northeastward. This trough will feed moisture north
over the Interior causing periods of light snow. Snow will be more
focused along the surface frontal boundary that lies from Denali
Park to Chandalar Lake. Will address snow below with the surface
front. Snow will shut off just south of this trough as moderate
chinook flows develops Thu. Will see south winds up to 40 mph
along the Alaska Range Thu into Fri.

A third short wave moving north will move to the Alaska Range Thu
night and over the Interior Fri. Expect downslope to prevent snow
in the Eastern Interior Fri but there should be some snow in the
Western Interior Fri.

Surface...
A 1009 mb low just north of Deadhorse will move to 100 nm north
of Deadhorse as a 1010 mb low by 4pm Wed...to 150 nm north of
Deadhorse by 4am Thu...then dissipating. FLurries along this low
will move offshore with the low.

An occluded front stretching from Denali to Chandalar Lake will
remain stationary through Thu am. A low over the Kenai Peninsula
will move to Denali Park as a 1008 mb low by 4am Thu...and to
near Bettles as a 1008 mb low by 4pm Thu...and to just north of
Barter Island as a 1006 mb low by 4am Fri. Snow along the front
will increase today as the surface low feeds moisture north along
the front. Expect 3-5 inches of snow along the front. Snow will
shut off south of the surface low on thu. Will see much lighter
amounts of snow with the low north of the Brooks Range.

&&

.DISCUSSION...
Models show similar solutions through Friday. See slight
differences in precipitation location but GFS showed locations of
snow best at 06z...so will use GFS locations. Start to see
differences in short wave features Fri night into the weekend.
Still agreement on the long wave pattern into next week. Will use
a more ensemble approach for this weekend into next week the long
wave trough remaining over Western Alaska with a ridge over the
NW Canada and Eastern Alaska.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory for AKZ219-AKZ220-AKZ221.

Brisk Wind Advisory for PKZ210-PKZ220.
&&

$$

JB MAR 17


000
FXAK68 PAFC 291306
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
506 AM AKDT Wed Mar 29 2017

.ANALYSIS AND UPPER LEVELS...
An upper level closed low remains over the Yukon Delta region
with an associated negatively tilted trough extending through the
Bristol Bay interior into the northern Gulf this morning. This
synoptic feature is reflected at the surface with a 998 mb low
located over the western Prince William Sound region with an
inverted trough extending northward towards the northern Alaska
Range. The radar imagery is showing a large swath of echoes
across the northern Gulf spreading inland into the Anchorage Bowl,
and the Mat-Su Valleys. The surface temperatures are ranging from
the lower 30s along the northern Gulf coastal communities, and in
the upper 20s for inland areas.

The Eastern Aleutians has an amplified ridge extending into the
central Bering with a weak closed upper level low located over the
Western Aleutians. While south of the Central Aleutians a 968 mb
storm force low is positioned at 44N 177W with an associated
occluded front approaching the Chain. The satellite imagery is
showing clear skies over the Southwest Alaska, and the Eastern
Bering. The Western Aleutians/Bering has marine layer stratus.
South of the Central Aleutians a storm force North Pacific low is
intensifying this morning with an associated occluded front
approaching the Central Aleutians.

&&

.MODEL DISCUSSION...
The models are coming into better agreement as the low pressure
system in the northern Gulf tracks into the Prince William Sound
region. The biggest forecast challenge remains the location of
the heaviest snowfall for our AOR this morning. As the upper level
trough swings through this evening, look for the snowfall to
taper-off to a showery regime. Meanwhile, the models have a storm
force low just south of the Central Aleutians with an eastward
storm-track following the Chain. The preferred models of choice
were the GFS/NAM, and the forecast confidence remains average.

&&

.AVIATION...
PANC...Look for steady snowfall with IFR to possible LIFR conditions
through midday today before transitioning to prevailing MVFR
conditions by this afternoon time-frame.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The negatively tilted upper trough will slowly push northeast
today. This will force the Prince William Sound surface low inland
as well, with snowfall moving inland and diminishing. There will
then be a brief break tonight before the next front works its way
into the gulf and south central Alaska from the southwest on
Thursday. This next system is much stronger than the current one.
It also has a lot more moisture, but most of the precipitation
will fall in coastal areas as the strong flow down-slopes off the
coastal mountains. The strong southerly fetch will also usher in
warmer air, with temperatures at many locations approaching or
even exceeding their normals for the first time this month.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Expect increasing clouds today with northerly flow across the
Southwest and easterly flow developing along the Alaska Peninsula.
A North Pacific low moves a front to the Peninsula late tonight
bringing snow and strong gusty winds through Friday. Added areas
of blowing snow to the forecast Thursday into Friday morning as
the front elongates and stretches north to Bristol Bay. The low
center approaches Sand Point Thursday afternoon, spreading snow
to the Kuskokwim by Friday morning. Gusty easterly flow increases
along the frontal boundary Thursday night which will bring a warm
air surge across the Aleutian Range; therefore, precipitation
will be mixed along and near the range. Temperatures warm across
the Southwest on Friday as the front weakens and fills.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Ridging along the northern Bering shifts south to the western
Aleutians by the end of the week as the strong North Pacific low
moves over the eastern Bering waters and Southwest. The main
impacts will be around the surface low as it moves near the
eastern Aleutians late tonight with gale to storm force winds
accompanied by rain and snow. Winds taper down late Friday as the
surface low fills and lifts north. Cold air advects from the
arctic to the Bering and the Aleutian chain into the weekend.

&&

.LONG TERM FORECAST (Days 3 through 7)...

(From yesterdays Forecast Discussion)

Thursday will be the day that the upcoming pattern change
will begin to be felt across much of Southern Alaska. An upper
level trough is still expected to amplify in the coming days as
strong jet support traverses with western periphery of the trough.
This will help to advect and warmer and wetter air mass up
towards Alaska. On Thursday, a surface low pressure south of Dutch
Harbor will begin to weaken. However, the frontal boundary
associated with this low and a surplus of upper level energy will
help a triple point low to develop south of the Alaska Peninsula.
This low is expected to move inland sometime late Friday morning
into Friday afternoon but a a bit of model divergence has made it
quite difficult to pinpoint all of the big details at this time.

With certainty, southern Alaska will see a pattern shift that
will entail temperatures warming a good bit above normal and
periods of rain and snow that will largely be confined to the
northern Gulf Coast. As it appears now, Anchorage and other areas
on the lee side of the Chugach Mountains will be downsloped from
any precipitation with impressive cross barrier flow developing.
Confidence is increasing that a chinook type pattern will set up
over the Anchorage bowl on Thursday and/or Friday which could
allow temperatures to warm into the lower to mid 40s. The
temperature forecast is heavily dependent on the amount of wind
that makes it into town but a warm up is nevertheless inevitable.
A mix of snow and rain will likely be seen along the coast
Thursday afternoon ahead of the frontal boundary but precipitation
across most of Southcentral Alaska will quickly change to all rain as
850 temperatures warm to near zero degrees Celsius and sfc to 850 mb
thicknesses rise quickly. Any precipitation from Friday morning
onward across Southcentral Alaska will likely be rain except for
portions of the Talkeetna Mountains, the Alaska Range and the
Aleutian Range where some minor snow accumulations could be seen.

Heading into the weekend, chances for rainfall and possibly a mix
of snow at times cannot be ruled out thanks to an active synoptic
pattern. A series of lows will pass through the gulf of Alaska
heading into next week but trying to come up with any low position
is near impossible this far out as the models are quite volatile
past 4 or 5 days. The weekend looks warm as temperatures will
likely remain above normal and no reprieve is seen through the
first half of next week.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 101.
MARINE...Storm Warning 131 155 172 174.
Gale Warning 119 120 130 132 136>139 150 160 165 170 171 173 175
176 180.
Heavy Frz Spray 179 185.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...PD
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KH
LONG TERM...MC


000
FXAK67 PAJK 291405
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
605 AM AKDT Wed Mar 29 2017

.SHORT TERM...today through Wednesday night. South to Southwest
flow aloft is the story over all of the AK Panhandle today. The
embedded waves in this flow will bring periods of enhanced
rainfall over the region in this wet pattern which will persist
through Wednesday night.

The main change in the forecast stems from a wave developing just
south of the Gulf of Alaska this afternoon which will move into
the southeast Gulf tonight. This will not bring a big change in
the winds but could extend the precipitation later into tonight
across much of SE Alaska and could shorten the break between
systems Thursday.

Current short term forecasts had some GFS guidance added. NAM also
had a good handle on the developing wave which was more diffuse on
the ECMWF. 06Z model runs of the GFS and NAM were continuing the
development of this feature.

.LONG TERM.../Thursday through Tuesday night/ A high end gale
force low is forecast to enter the western gulf on Thursday. Gale
force winds with the associated front will arrive over outer coast
on Thursday evening and extend from Cape Suckling south pas the
Dixon Entrance. Peak conditions expected on the inside late
Thursday night with gales forecast for Clarence Strait, Sumner
Strait, southern portions of Chatham Strait, and Cross Sound.
Elsewhere on the inside, small craft winds forecast except for
northern Lynn Canal, where a parallel gradient should result in
winds 20 kt or less.

Precipitation from this front will arrive along the outer coast
late Thursday afternoon or Thursday evening. Significant low level
warm air advection associated with this front will push snow
levels higher, limiting snow to the higher elevations of the
highways.

WPC, the 00Z GFS, and the 12Z ECMWF model runs presented moderate
to good agreement at 500 mb on the placement of troughs, short
waves, and upper level ridges. A ridge extending from BC southwest
to coastal waters west of Washington State will become suppressed
over the weekend but then rebuild early next week. Temperatures
from Thursday into Friday were warmed slightly.

Confidence in the extended range forecast is average.


&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ051-052.
Small Craft Advisory due to Seas for PKZ022-041>043-053.
&&

$$

EZ/Bezenek/Fritsch

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