Storm Warning 163, NWS Anchorage, AK

409 
FZAK62 PAFC 220027
OFFALU

Offshore Waters Forecast
National Weather Service Anchorage AK
327 PM AKST Thu Dec 21 2017

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.

PKZ499-221415-
327 PM AKST Thu Dec 21 2017
.SYNOPSIS FOR CENTRAL BERING SEA...
A 976 mb low crosses over the AKPEN and into the Bering this 
afternoon and moves to 60N 174W at 975 mb Fri morning. The low 
then moves north over Kamchatka. A front associated with a low in
the western Gulf extends across the eastern Bering Fri morning
through Sat afternoon.

$$

PKZ411-221415-
Bering Sea Offshore West of 180 and East of the International
Dateline-
327 PM AKST Thu Dec 21 2017

...GALE WARNING FRIDAY...

.TONIGHT...NW wind 15 to 30 kt. Seas 8 to 16 ft. Freezing spray.
.FRI...W wind 20 to 35 kt. Seas 9 to 14 ft.
.FRI NIGHT...W wind 15 to 30 kt. Seas 8 to 13 ft. Freezing spray.
.SAT...W wind 15 to 30 kt. Seas 7 to 12 ft.
.SAT NIGHT...W wind 10 to 25 kt. Seas 6 to 11 ft.
.SUN...NW wind 10 to 25 kt. Seas 6 to 11 ft.
.MON...NE wind up to 20 kt. Seas 4 to 8 ft.
.TUE...SE wind 20 to 35 kt. Seas 12 to 20 ft.

$$

PKZ412-221415-
Bering Sea Offshore 171W to 180 and North of 56N-
327 PM AKST Thu Dec 21 2017

...GALE WARNING THROUGH FRIDAY NIGHT...

.TONIGHT...NE wind 30 to 45 kt. Seas 14 to 22 ft. Rain and snow.
.FRI...NW wind 30 to 45 kt. Seas 12 to 20 ft. Snow showers.
.FRI NIGHT...W wind 20 to 35 kt. Seas 12 to 19 ft. Freezing spray.
Snow showers.
.SAT...W wind 10 to 25 kt. Seas 8 to 13 ft.
.SAT NIGHT...NW wind 15 to 30 kt. Seas 7 to 12 ft.
.SUN THROUGH MON...N wind 10 to 25 kt. Seas 6 to 11 ft.
.TUE...E wind up to 20 kt. Seas 5 to 8 ft.

$$

PKZ413-221415-
Bering Sea Offshore 171W to 180 and South of 56N-
327 PM AKST Thu Dec 21 2017

...STORM WARNING TONIGHT...

.TONIGHT...NW wind 35 to 50 kt. Seas 13 to 21 ft.
.FRI...NW wind 30 to 45 kt. Seas 16 to 23 ft.
.FRI NIGHT...W wind 20 to 35 kt. Seas 10 to 18 ft. Freezing spray.
.SAT...W wind 10 to 25 kt. Seas 8 to 13 ft.
.SAT NIGHT...W wind 10 to 25 kt. Seas 7 to 12 ft.
.SUN...W wind 10 to 25 kt. Seas 8 to 13 ft.
.MON...SW wind up to 15 kt. Seas 4 to 8 ft.
.TUE...E wind 10 to 25 kt. Seas 5 to 10 ft.

$$

PKZ414-221415-
Bering Sea Offshore East of 171W-
327 PM AKST Thu Dec 21 2017

...GALE WARNING THROUGH FRIDAY NIGHT...

.TONIGHT...E wind 25 to 40 kt. Seas 10 to 18 ft. Rain.
.FRI...SE wind 20 to 35 kt. Seas 9 to 17 ft. Rain and snow showers.
.FRI NIGHT...W wind 20 to 35 kt. Seas 9 to 17 ft. Snow and rain
showers.
.SAT...NW wind 20 to 35 kt. Seas 10 to 18 ft.
.SAT NIGHT...NW wind 20 to 35 kt. Seas 9 to 17 ft.
.SUN...NW wind 15 to 30 kt. Seas 9 to 17 ft.
.MON...SW wind up to 10 kt. Seas 4 to 9 ft.
.TUE...NE wind up to 15 kt. Seas 5 ft.

$$

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
408 PM AKST Wed Dec 20 2017

.ANALYSIS AND UPPER LEVELS...
The remnants of a once powerful Bering Sea low is moving east as
a low amplitude (and deamplifying still) shortwave trough tracks
across the ALCAN. Weak upper ridging is building over Southwest
Alaska ahead of a digging upper level trough over the western
Bering Sea and into the North Pacific. There is a ridge over the
northeast Pacific and a cutoff low to it's west near 38N. Closer
to home, a storm force front is stalled over the central Bering.
At the surface across Southcentral, the dichotomy in the pattern
is clear as there is a weak but obvious up-inlet flow over Cook
Inlet while a subtle offshore flow remains from Prince William
Sound eastward.

&&

.MODEL DISCUSSION...
The numerical models are in excellent agreement with the large
scale general synoptic pattern through the weekend. A duo of
powerful surface lows are expected to reinforce a strong
baroclinic zone over the eastern Bering Sea Thursday night and
Friday night, and while there remains some disagreement still with
the exact track of the second low, the models are now largely in
good agreement with increase forecast confidence of impacts across
Southwest Alaska and the eastern Bering Sea. The NAM hi-res was
favored over Southcentral for local gap winds while the GFS was
favored for the strong front over the Bering Sea and Southwest
Alaska.

&&

.AVIATION...
PANC...VFR conditions will develop late this afternoon. Some
patchy fog and/or low stratus is possible over the terminal
beginning around midnight, and clearing by early Thursday
afternoon.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A weak upper level trough will move across the Copper River Basin
this evening providing enough instability to trigger some snow
showers in the residual moisture left from the previous system
than moved through overnight. This will be followed by rapidly
diminishing cloud cover and the onset of a strong radiational
cooling inversion over the Basin that will likely result in low
stratus and fog throughout much of the low lying areas in the
Basin. Over the Kenai Peninsula and Cook Inlet we should also see
an inversion with areas of fog, however, the down Inlet flow will
help to mix out some of the inversion, thus the fog should be
limited to wind protected areas. There is a chance the fog will
persist well into the day tomorrow under a ridge aloft that will
build over the Copper River Basin.

Another storm will move to south of the Alaska Peninsula Thursday
resulting in a tight gradient and strong wind extending northeast
to the Barren Islands. This will also push rain to Kodiak Island.
We will back off on the onset of the rain along the outer coast of
the Kenai Peninsula to account for a slightly slower progression
of the storm and precipitation field in the latest model run.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Sensible weather-wise, much of the southwest will be dry for the
ensuing 24 hr period which will prove to be a lull before the next
storm. Thursday evening, the precipitation shield will move into
the AKPEN, Eastern Bristol Bay and up the Kuskokwim Delta. The
projected thermal profiles suggest another wintry mix at the onset
of the storm. However, by Friday morning the precip type will
change over to rain along the coast. The models are in sync with
the tight pressure gradient over the AKPEN and Bristol Bay
Thursday afternoon and Friday. Gaps and downslope wind prone
areas along the AK pen will get hammered with winds. Confidence
begins to wane over the weekend due to the placement of a
secondary low but there is potential that this secondary low could
bring a prolonged period of strong/gusty winds to Bristol Bay and
the Kuskokwim Delta into Saturday. Stay tuned for more details.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Unsettled weather will continue as a series of lows trek across
the region. The forecast period commences with a surface low near
Adak. This low will continue to produce gusty winds across the
Aleutians. As time elapses, a second system will move into the
region from the southwest/North Pacific which will keep the tight
pressure gradient over the Eastern Aleutians. In addition to gusty
winds, the models ping into a deep fetch of moisture associated
with the warm sector. By Friday, a new disturbance will approach
Attu Island and Shemya.

&&

.LONG TERM FORECAST (Friday through Tuesday)...
By Friday, southern Alaska will be in the thick of things
weather-wise, with a low pressure system in the northern Bering
and another one close on its heels south of the AK Pen. This will
bring a strong series of fronts through Southwest Alaska, and
Bristol Bay and the Bering side of the AK Pen can expect some very
windy conditions. Precipitation on the Pacific side of the AK Pen
and Kodiak Island will also be significant, although not as much
as initially shown several days ago. On the western or backside of
these low pressure systems, some strong cold air advection will
move into the Pribilofs and Eastern Aleutians, which will bring
some heavy snow showers and possible blowing snow through Saturday
night.

On Saturday, the ridge holding those lows in place will weaken,
allowing the front over Kodiak to slide eastward and bring
precipitation to the southern Kenai peninsula. A secondary low is
forecast to form just south of the Kenai and move into the Gulf of
Alaska, which should keep down-inlet windflow for Southcentral and
keep the weekend cool. Unfortunately, this northerly flow looks to
remain pretty dry, decreasing any chances of snow for the
northern portions of Southcentral. Tuesday looks like it will
clear out over most of the mainland. By Wednesday, the forecast
models are struggling to agree on a solution. Currently, the GFS,
EC and Canadian agree on bringing a strong low up toward the AK
Pen from the north Pacific. However, previous runs have shown
significantly different solutions, so confidence in the day 7
forecast is low.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Watch 161.
MARINE...Storm Warning 130>132 150 155 160 165 180 181 185.
 Gale Warning 119 120 136>139 170>179.

&&

SYNOPSIS AND MODEL DISCUSSION...JA
SOUTHCENTRAL ALASKA...SA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PJS
LONG TERM...LF