Gale Warning 781, NWS Anchorage, AK

907 
FZAK62 PAFC 181204
OFFALU

OFFSHORE WATERS FORECAST
NATIONAL WEATHER SERVICE ANCHORAGE AK
304 AM AKST SUN DEC 18 2016

OFFSHORE WATERS FORECAST FOR THE BERING SEA

WIND FORECASTS REFLECT THE PREDOMINANT SPEED AND DIRECTION
EXPECTED. SEA FORECASTS REPRESENT AN AVERAGE OF THE HIGHEST
ONE-THIRD OF THE COMBINED WIND WAVE AND SWELL HEIGHT.

PKZ499-190230-
304 AM AKST SUN DEC 18 2016
.SYNOPSIS FOR CENTRAL BERING SEA...
A 946 MB LOW NEAR 54N 175W MOVES TO 55N 172W AT 958 MB LATE
TONIGHT...THEN MOVES TO 53N 171W AT 977 MB LATE MON NIGHT. AN
ASSOCIATED FRONT OVER THE EASTERN ALEUTIANS AND ALASKA PENINSULA
DISSIPATES TODAY

$$

PKZ411-190230-
BERING SEA OFFSHORE WEST OF 180 AND EAST OF THE INTERNATIONAL
DATELINE-
304 AM AKST SUN DEC 18 2016

.TODAY...N WIND 20 TO 30 KT. SEAS 12 TO 17 FT. WIDESPREAD RAIN
SHOWERS.
.TONIGHT...N WIND 25 KT. SEAS 11 TO 15 FT.
.MON...N WIND 15 TO 25 KT. SEAS 10 TO 13 FT.
.MON NIGHT...N WIND 10 TO 20 KT. SEAS 8 TO 12 FT.
.TUE...W WIND UP TO 15 KT. SEAS 5 TO 9 FT.
.WED THROUGH THU...W WIND UP TO 15 KT. SEAS 3 TO 7 FT.

$$

PKZ412-190230-
BERING SEA OFFSHORE 171W TO 180 AND NORTH OF 56N-
304 AM AKST SUN DEC 18 2016

...GALE WARNING THROUGH TONIGHT...

.TODAY...NE WIND 25 TO 40 KT. SEAS 16 TO 19 FT. RAIN SHOWERS AND
SNOW SHOWERS.
.TONIGHT...NE WIND 25 TO 35 KT. SEAS 14 TO 18 FT.
.MON...NE WIND 20 TO 30 KT. SEAS 11 TO 16 FT.
.MON NIGHT...N WIND 15 TO 25 KT. SEAS 8 TO 12 FT.
.TUE...NW WIND UP TO 20 KT. SEAS 5 TO 8 FT.
.WED...S WIND UP TO 10 KT. SEAS 3 TO 6 FT.
.THU...SE WIND UP TO 15 KT. SEAS 3 TO 7 FT.

$$

PKZ413-190230-
BERING SEA OFFSHORE 171W TO 180 AND SOUTH OF 56N-
304 AM AKST SUN DEC 18 2016

.TODAY...NE WIND 15 TO 30 KT. SEAS 14 TO 18 FT. WIDESPREAD RAIN
SHOWERS AND SNOW SHOWERS.
.TONIGHT...N WIND 20 TO 30 KT. SEAS 12 TO 16 FT. RAIN SHOWERS AND
SNOW SHOWERS.
.MON...N WIND 15 TO 25 KT. SEAS 11 TO 15 FT.
.MON NIGHT...N WIND 15 TO 25 KT. SEAS 11 FT.
.TUE...NW WIND UP TO 20 KT. SEAS 6 TO 9 FT.
.WED THROUGH THU...S WIND 10 TO 20 KT. SEAS 5 TO 8 FT.

$$

PKZ414-190230-
BERING SEA OFFSHORE EAST OF 171W-
304 AM AKST SUN DEC 18 2016

...GALE WARNING TODAY...

.TODAY...E WIND 25 TO 40 KT EXCEPT SW 30 KT S OF THE PRIBILOF
ISLANDS. SEAS 13 TO 21 FT.
.TONIGHT...SE WIND 15 TO 30 KT. SEAS 13 TO 21 FT.
.MON...NE WIND 10 TO 25 KT. SEAS 8 TO 13 FT.
.MON NIGHT...N WIND 15 TO 30 KT. SEAS 9 TO 12 FT.
.TUE...NW WIND 10 TO 25 KT. SEAS 6 TO 10 FT.
.WED...W WIND UP TO 20 KT. SEAS 3 TO 8 FT.
.THU...S WIND UP TO 15 KT. SEAS 3 TO 7 FT.

$$

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
446 AM AKST Sat Dec 17 2016

.ANALYSIS AND UPPER LEVELS...
The controlling planetary-scale features are a sprawling upper low
center from Kamchatka eastward through the west coast of Alaska,
and an eastern Pacific ridge that stretches from the mid-
latitudes northward through the arctic. The east Asian jet is
active, and spitting disturbances into the longwave trough. Of
these, two main features stand out on this morning's water vapor
imagery. The first is baggy trough stretching from the southwest
mainland into the western Gulf. There is fairly cold air aloft in
the trough, as the moisture has a convective, open-cell look to
it. The second is a stronger shortwave trough is entering the
longwave near the western/central Aleutians. The jet remains south
of the Aleutians, with the predominant storm track from the
Aleutians into the Gulf.

The first trough is pushing into the Gulf early this morning, with
the weak frontal boundary already pushing inland. Turnagain winds
have pushed into west Anchorage, starting our snow event as rain,
but reflectivity on the Kenai radar is above 40 dbz, which should
be enough to change over to snow fairly quickly. Out west, a
hurricane-force low is currently undergoing bombogenesis as it
approaches the central Aleutians.

&&

.MODEL DISCUSSION...
Guidance finally seems to have converged on a solution for the
snow in the Cook Inlet region today. Not much difference in the
dynamics among models, or precipitation output. High-res was
favored for terrain handling. Bigger differences are evident with
the cyclone developing out west with a fair spread among models on
placement of the low, which will make a big difference on peak
wind speeds over the Central Aleutians. The western domain favored
the GFS for this system.

&&

.AVIATION...
PANC...The main challenges for the TAF this morning are Turnagain
winds and snow changeover. Radar trends would support a quick
changeover to snow early this morning, but if Turnagain winds
hold on longer, so will warmer temperatures and rain at the
surface. After changeover, expect moderate snow to persist for a
few hours with the highest intensity before mid-morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The combination of a broad upper trough and low level convergence
as cold air moves up Cook Inlet will lead to development of a
moderate to heavy band of snow from Anchorage northwestward to
the Mat Valley and southern portions of the Susitna Valley.
Expect the band to move steadily northward and not sit too long
in any one location. There is still some uncertainty in total
snow accumulation, with precip starting as rain in some locations
before the cold air arrives and uncertainty in exactly where the
heaviest snow will fall. It generally looks most favorable for
heavier amounts along the Anchorage hillside and East Anchorage
on up to Eagle River and the Palmer and Wasilla area. Have bumped
up snowfall totals a bit from the previous forecast due to higher
confidence in the snow band moving through as well as the
convective nature of snow in radar imagery.

The upper trough will slowly exit to the north tonight with precip
rapidly tapering off most areas by midnight. Low-level flow will
shift around to the north and strengthen out ahead of a storm-force
front moving in from the Aleutians and North Pacific. A strong jet
stream combined with cold air moving in behind this will lead to
development and deepening of a triple point low over the northwest
Gulf on Sunday. Have made significant upward adjustments to the
wind and waveheight forecasts to capture this deep low.
Precipitation will rapidly move northward Sunday, initially
affecting the Gulf coast and Kodiak Island. The strong offshore
flow out ahead of it will keep the remainder of the area dry and
will also limit snow totals across the interior Western prince
William Sound zone, including Turnagain Pass and Alyeska. As the
low weakens Sunday night there is a chance of light snow across
the Cook Inlet region as moisture advects over mountains and a
separate short-wave trough moves up from the south.

&&

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

A colder air mass has settled over Southwest this morning with the
remnants of the frontal zone now moving into Cook Inlet. An upper
trough aloft is helping to support areas of snow showers in a
general southwest flow. These will diminish this morning as
another very weak trough axis moves onshore along the coast. This
will bring rain and snow showers mainly to the Kuskokwim Delta
before this trough weakens as it moves inland. Snow will continue
to accumulate near the Alaska Range through the day as a favorable
upslope flow continues.

Attention quickly turns to a vigorous occluded front which will
move north toward the Bristol Bay region on Sunday morning. East
to northeast winds will increase along with increasing snow rates.
The precipitation rates will be highest west of King Salmon. Along
with gusty northeast winds as high as 30 MPH, expect some areas of
blowing snow and reduced visibility before the front weakens
Sunday evening. Light snow will then continue as the front stalls
through Sunday night from King Salmon north.

&&

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

A rapidly deepening low just south of Amchitka will become the
focus of the forecast period as powerful hurricane force winds
develop on the back side of the low where strong cold air
advection will wrap in from the west. Southeast winds of 45-70 MPH
will move from Adak/Atka this morning to the Alaska Peninsula by
tonight. These strong winds will be rather brief (3-6 hours) as
the front races eastward. As the actual surface low moves north of
Adak, a prolonged period of hurricane force westerly winds (65-90
MPH) will impact the Central Aleutians through Sunday before
gradually dropping off as the low weakens. Showers will encompass
most of the Bering and Aleutians as this low remains in place
through Sunday night.

&&

.LONG TERM FORECAST (Days 3 through 7...Sun night through Fri)...

Fast progressive flow will develop across the forecast area late
this weekend through the end of the workweek. The initial low near
Kodiak Island Sun night will swing a front into the north Gulf
coast on Mon. Snow will accompany this front, mainly over the
coastal mountains with some bleeding inland.

The next low over the central Bering Sun night will move to the
north Gulf coast by Wed. This low will then decay in place through
the rest of the week. Rain and snow will affect the eastern
Aleutians and Southwest Ak through Wed, and then snow is expected
again along the coastal mountains of Southcentral through the end
of the week. Some snow will also cross the coastal mountains
during the middle of the week.

The final low will develop Wed over the extreme western Bering
and reach the Pribilofs by the end of the week. This will bring
rain and snow to the Aleutians and Bering during the second half
of the week. Some strong wind will also affect the island with
this system.

The run to run consistency demonstrated by the models is beginning
to improve. Confidence is now moderate with the timing of the
lows, as well as the location of precipitation.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning 187.
MARINE...Hurricane 176 177 178.
         Storm 155 165 170 172 173 174 175.
         Gale 150 160 171 179 180 181 185.

&&

SYNOPSIS AND MODEL DISCUSSION...MTL
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
LONG TERM...DS