National Weather Service United States Department of Commerce


000
FXAK68 PAFC 181431
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
531 AM AKST Sat Nov 18 2017

.ANALYSIS AND UPPER LEVELS...

A Gulf low departing into the northeast Pacific this morning is
helping to dig a longwave trough centered over the Alcan border
region while a ridge builds over the central Bering Sea. This has
allowed the bulk of the southern mainland to return to a more
amplified offshore flow pattern, leaving gusty outflow winds along
the Gulf coast as the primary sensible weather impact. Skies have
cleared out over Southcentral AK once again with the exception of
some patchy fog and stratus lingering over parts of Cook Inlet
and the Matanuska Valley. Skies are mostly overcast across
Southwest AK as mid level cloud cover streams in over the top of
the Bering ridge. A warm front associated with a low over far
eastern Russia extends southeast along the Kuskokwim Delta
coastline and is poised to bring another round of mixed
precipitation to the Delta as it moves inland today. A trailing
cold front is making slow eastward progress through the Western
Aleutians.

&&

.MODEL DISCUSSION...
Models are in generally good short term agreement as the pattern
remains very progressive over the coming days. The Bering Sea
ridge will quickly break down this weekend as a strong upper level
wave drops out of the Bering Strait region Saturday night and
moves into the western Gulf on Sunday, spreading significant
winter weather and strong winds over a wide swath of the eastern
Bering and Southwest AK. Some differences remain regarding the
placement of a surface low developing east of Kodiak Sunday
morning, which will have large implications on precipitation type
and intensity for Kodiak Island. Preferred the GFS solution as
somewhat of a middle ground for the morning forecast package.

&&

.AVIATION...
PANC...VFR conditions and light northerly winds will persist
through late Saturday night. Snow will spread back into the
terminal from the west early Sunday morning, dropping conditions
to MVFR/IFR after 12z.

&&

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

Strong gap/outflow conditions and gales over the western Gulf
will weaken through today as surface pressure gradients and upper
wind support wanes. The focus then turns to the frontal trough and
associated triple point center moving into the western Gulf
tonight. Models are initially in agreement with the occluded
portion of the front as it spreads overrunning snow to
Southcentral beginning Sunday morning. The triple point is another
matter. The preferred solution is to take the triple point which
develops near Kodiak Island Sunday morning and carry it just to
the east and then retrograde the system to the west/southwest some
Sunday night. This will be a fairly strong low that will bring
gales and storm force winds to the Gulf waters Sunday and Sunday
night. The result of this solution for the Southcentral Mainland
would be to spread snow to along the north Gulf coast through
Sunday afternoon with the heaviest over the Kenai Peninsula. Snow
amounts may approach advisory levels over the western Kenai by
Sunday afternoon. Snow will tapper off throughout the evening and
overnight hours over the Mainland and be followed outflow winds
along the north Gulf coast.

Kodiak island will likely see warm advection with a mix of rain
and snow with the front and developing triple point Sunday. The
preferred solution of keeping the low just to the east would
likely hold out any significant cold advection and tend to keep
the precipitation mixed or a very wet snow. So with the strong
winds moving in we are not expecting significant reductions in
visibilities in blowing snow with the strong northerly winds
develop during Sunday and Sunday night. A slight change in track
however would result in potential heavier snowfall and significant
blowing snow. Stay tuned for updates.

&&

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

The storm expected to impact Southwest Alaska remains on track.
The storm`s center is still over eastern Russia, however the
storm`s warm and cold fronts extend well south of the center of
the low across the Bering. The warm front is over the eastern
Bering, and is responsible for the snow and mixed precipitation
already being reported along the coast this morning. The cold
front and arguably the bigger weather maker is the cold front now
racing across the western Bering. As the warm front slowly pushes
into mainland Southwest Alaska, the snow will change over to rain
first at the coast and gradually through much of the Kuskokwim
Delta west of the Kuskokwim Mountains. During that transition from
snow to rain this afternoon, a brief period of freezing rain is
possible, but the warm air is expected to scour out the
subfreezing surface air quickly, with a little help from the weak
November sun.

Further south through Bristol Bay, snow will begin around midday
and push eastward to the Alaska Range by the evening. At the
coast, the warm air will transition the snow to rain during the
afternoon, but with slightly weaker onshore winds, it will have
more difficulty scouring out all of the cold air. Thus a longer
duration freezing rain is expected north of King Salmon through
Koliganek, New Stuyahok, and Igiugig, though ice accumulations
should remain less than a tenth of an inch with a wide variety of
precipitation types expected. Inland Bristol Bay and the entire
Kuskokwim Valley are still expected to pick up close to a foot of
loose, powdery snow. In the windier areas, that will cause blowing
snow concerns both as the snow is falling and well after the storm
ends through Monday morning.

The cold front will race across the Bering today and reach the
coast tonight. It is the leading edge of very cold air, which
coupled with the rapidly intensifying low over the Bering Strait
will cause a large area of storm force winds with gusts over
hurricane force. This is most likely in Southwest Alaska along the
coast of the Kuskokwim Delta and especially Nunivak Island.

&&

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

A storm over Russia with distinct warm and cold fronts over the
Bering are the primary weather features this morning. The warm
front will move into Southwest Alaska this morning. The cold front
and the arrival of a much colder air mass will be the catalysts
for strong winds across much of the Bering. The first land to be
impacted will be the Pribilofs. The cold front will race through
this afternoon, but the highest winds will really be associated
with the strengthening low over the Bering Strait late Saturday
night that will dramatically increase the winds out of the
northwest late tonight through Sunday morning. A few hours later,
those same winds will reach the Alaska Peninsula and Eastern
Aleutians, where gusts as high as 90 mph through bays, passes, and
channeled terrain will be possible.

The strong winds associated with the low will diminish late Sunday
night through Monday morning as another area of warm high pressure
builds over the central and western Bering. Yet another low
tracking along the Russian Coast will cause yet another cold front
with another blast of cold air on strong winds to traverse the
Bering Monday for the western Bering and Monday night for the
remainder of the Bering, though these strong winds will be more
out of the west.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Expect near to below normal temperatures with periodic snow across
the southwest, and periodic cloudiness for Southcentral Alaska.
Gap winds will pulse up with every exiting disturbance.

Monday evening begins day 3 with an exiting system in the Gulf of
Alaska. Dry conditions will take hold over much of southern Alaska
within an outflow pattern, mainly along the north Gulf coast.
Overall, the upper level pattern remains very progressive with
strong, discrete disturbances propagating from the northwest
Pacific into the Bering Sea. Each of these systems will send a
surface low pressure east of Kamchatka while sending a front from
west to east across the Bering. However, troughing from northwest
Canada southward will turn the storm track from the Bering into
the Gulf of Alaska. As far as sensible weather is concerned, the
periodic fronts will push snow onto the mainland while the front
falls apart as it moves west to east.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning: 155 181 185 195
Winter Weather Advisory: 121 152 161
MARINE...Storms: 131 132 155 165 170 172 179 180 181 185 412 414
Gales: 119 120 138 150 160 171 173 174 178 351 352 411 413

&&

$$

SYNOPSIS AND MODEL DISCUSSION...CB
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JPW
LONG TERM...TP


839
FXAK69 PAFG 181321
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
421 AM AKST Sat Nov 18 2017

.SYNOPSIS...
Aloft...
A long wave pattern consisting of ridge over the Bering Sea and
West Coast of Alaska and trough over NW Alaska eastern Gulf of
Alaska will persist through next week. A series of strong short
wave troughs will ride over the top of this ridge and bring a
series of strong storms with rain, snow and strong winds into the
West Coast of Alaska while the eastern Interior will remain cold
into next week.

A weak short wave trough over the eastern North Slope will move
to Central to Inuvik by 3pm sat then move east of the Alcan Border
tonight. Expect a few flurries with this.

A strong short wave in the Western Bering Sea will move along the
Dateline by 3pm Sat, over the West Coast of Alaska by 3am Sun,
and then moving into the Gulf of AK Sun PM. This is bringing a
strong storm into the west coast today and western Interior
tonight with strong winds, heavy snow, blizzard conditions, and
freezing rain. See surface discussion for details.

A second strong short wave trough moving into the western Bering
Sea Mon, into the West Coast of Alaska Tue, and to the eastern
Interior Wed. Another strong storm with strong winds and moderate
to heavy snow will accompany this trough.

A third strong trough moves across the Bering Wed and into the
West Coast Wed night.

Surface...
A low pressure trough from Inuvik to Deadhorse will move to Old
Crow to Barrow by 3pm Sun. Expect few flurries along this trough.
SW winds over the Arctic Coast will turn NE north of the trough
late Sat.

A trough stretching from Point Lay to Denali will weaken today.
Stratus and flurries along this will diminish today.

A 995 mb low just west of Anadyr will move over the Chukotsk
Peninsula as a 985 mb low by 3pm Sat, to the Bering Strait as a
980 mb low by 3am Sun, to Sparrevohn as a 994 mb low by 3pm Sun,
and then continue SE.

A warm front extending SE from this low, will move to Gambell to
Bethel by 3pm Sat with a cold front occluding the warm front NW
of Gambell and then extending from Gambell to St Paul Island. The
front will rapidly occlude from the Bering Strait to a triple
point near Dillingham by 3am Sat. After this time there will be a
hang back occlusion from Sparrevohn to the Bering Strait through
3pm Sun then dissipating Sun night.

There is heavy snow ahead of the warm/occluded front that will
change to rain in the warm sector, then chance back to snow with
the cold front. This rain will freeze on the cold ground in zones
214 and southern 215 today as the warm sector moves over it.
Expect 8-12 inches of snow just north of the front, with lesser
amounts in northern zones 216 and in zone 209. Expect one quarter
inch or more ice accumulation in zones 214 and southern 215 today,
so those areas will only get 4-8 inches of snow. Snow will taper
off rapidly Sunday as the low and front moves south.

Expect SE winds 25-35kt ahead of the warm front which will cause
blizzard conditions in areas with falling snow. Expect winds to
turn W 25-30 kt west of the Occluded front, then NW 35-45kt in the
SW quadrant of the low center. This could bring Blizzard
conditions to zones 213 and 214 after the occluded frontal
passage. Since the front winds do not last for more than 12 hrs
this will likely only cause high surf to the Yukon Delta and
Stebbins west of zone 212 tonight and Sun with a storm surge of 3
feet. This will cause water to rise on the Yukon River in the
Delta tonight and Sun as well.

High pressure developing over the Eastern Interior tonight will
persist into Sun then weaken. This will cause easterly drainage
winds along the Tanana and Yukon Rivers to develop tonight and
continue into Sun as the pressure gradient increases with the low
approaching the West Coast.

A second strong low will move from the western Bering to near
Anadyr on Mon and over the southern Chukchi Sea Tue. This will
bring another round of strong winds, snow, blowing snow and
possible blizzard conditions to the west Coast Mon night and Tue.
This could bring a significant storm surge and possible coastal
flooding to the West Coast of Alaska Tue into Wed, but still much
uncertainty on this. Will keep eye on this feature for further
developments.

&&

.DISCUSSION...
Deterministic Models initialize well at H500 and show similar
solutions through 3pm Mon. By the middle of next week start to
see significant differences on strength timing of short wave
troughs. At the surface all models are about 4 mb too weak at 06Z
Sat on the surface low west of Anadyr. Expect low will remain a
few mb deeper than models indicate through Sat night so will
adjust winds up a few kt over the Bering as a result. The GFS and
ECMF move this low southeast tonight and Mon more slowly than the
NAM. Favor the slower GFS and ECMF movement since the low will
likely be a bit deeper than indicated.

Models do differ on northerly extent of the precipitation, with
the GFS and ECMF moving precipitation into Kotzebue while the NAM
keeps most of the precip further south. The GFS also lessens the
precip amounts Sat night compared tot he ECMF and NAM. Favor the
lesser amounts Sat night on the GFS as the triple point is moving
rapidly southeast and the heaviest precip should move south with
the triple point. So favor the GFS precip overall.

Coastal Hazard Potential Days 3 and 4...
High surf for the Yukon Delta today and tonight.

A strong storm is expected to move from the western Bering to
near Anadyr on Mon and over the southern Chukchi Sea Tue. This
could bring a significant storm surge and possible coastal
flooding to the West Coast of Alaska Tue into Wed, but still much
uncertainty on this. Will keep eye on this feature for further
developments.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory for AKZ212-AKZ214.

Winter Storm Warning for AKZ214-AKZ215.

Blizzard Warning for AKZ207-AKZ209-AKZ210-AKZ211-AKZ212-AKZ213.

Winter Storm Watch for AKZ216.

Heavy Freezing Spray Warning for PKZ215-PKZ220-PKZ225-PKZ230-
PKZ235.

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

$$

JB NOV 17



728
FXAK67 PAJK 181400
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
500 AM AKST Sat Nov 18 2017

.SHORT TERM...Saturday through Sunday night...Satellite imagery
and surface analysis indicate gale force low dissipating as it
slides SE across the SE gulf. This will result in diminishing
showers and increasing Nly outflow winds today. Winds will rise to
gales over Lynn Canal, Cross Sound and Yakutat Bay today as
gradient tightens, with SCA over the N inner channels and outer
coast. Outflow also resulting in strong winds along the Klondike
Hwy today. Lowered winds slightly over downtown Juneau and Douglas
because the only Taku ingredient to mention is cross barrier
flow, while a critical layer and inversion are lacking. Clearing
skies overnight into Sun will allow temps to fall sharply after
sunset resulting in cooler temps Sun AM across SE AK. Models
remain in fairly good agreement with another low developing over
the W gulf before sliding SSE across the gulf heading into Mon
although the NAM remains an easterly outlier with the associated
front. This front will begin to impact the N Gulf coast late Sun
night before pushing precip into the panhandle heading into Mon.
Inherited forecast represented this thinking well with only minor
adjustments for local effects. Forecast confidence remains good
through the period.

.LONG TERM.../Monday through Saturday/It is the time of year where
only short reprieves between low pressure systems are common,
this week will be just that way. By Monday, a low center will be
in the south-central gulf/North Pacific, then by early Wednesday
morning the low will cover much of the eastern gulf. Confidence is
good through this time and then starts to falter a bit with more
differences between the models. Used the EC to do a small blend to
the current forecast, an ensemble approach would continue to be
prudent.

By this time temperatures will have warmed over most of the
southern half of the Panhandle to bring in rain for the south and
a mix of rain and snow in the central during the day. Temperatures
will still be cold enough to change to all snow in the
overnight/early morning hours for these areas. The warmer air
should advance up to the Elfin Cove/Gustavus/Hoonah/Juneau
corridor on Thursday. This is where some confidence slips as to
whether the precipitation in the central Panhandle, as far north
as Elfin Cove/Juneau will be snow, rain or a mix of both. Outer
coastal areas will be a more certain rain for the precipitation
type. By the weekend Skagway and Haines will be waffling between
rain and snow for precipitation type, for the near sea level
locations and remaining snow for the highways.

There are reasonably healthy QPF amounts for the southern
Panhandle which could give several inches of rain and/or snow
Tuesday night/Wednesday. Then spread into the central Panhandle
Wednesday. With temperatures rising above freezing during the day
for most locations and then falling below at night amounts will be
tricky. Downsloping winds will likely keep some local areas in
the north relatively drier.

Brisk winds continue around the northern Panhandle with the
northerly wind. In the south the winds will be getting the
influence of the low in the gulf leading to a southeasterly wind.
Wind speeds for much of the Panhandle will range from 15 to 25
mph with higher gusts. A lot of SCA, with some Gales on Monday.
Winds will be on a slow diminishing trend through the week, but
stay mindful for the strong outflow winds in the north through mid
week. These outflow winds will linger between Yakutat and Dry Bay
through Thursday.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind through Sunday morning for AKZ018.
MARINE...Gale Warning for PKZ012-013-022-053.
Small Craft Advisory for PKZ011-021-031-032-043-051-052.
Small Craft Advisory due to Seas for PKZ041-042.

&&

$$

BC/KV

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