Small Craft Advisory 587, NWS Anchorage, AK

053 
FZAK52 PAFC 102343
CWFALU

Coastal Waters Forecast
National Weather Service Anchorage Alaska
343 PM AKDT Thu Aug 10 2017

Coastal Waters Forecast for Southwest Alaska+Bristol Bay+The
Alaska Peninsula Waters and the Aleutian Islands up to 100 nm out.

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.

PKZ199-111230-
343 PM AKDT Thu Aug 10 2017
.SYNOPSIS FOR SOUTHWEST ALASKA+BRISTOL BAY+THE ALASKA
PENINSULA WATERS AND THE ALEUTIAN ISLANDS...

Bogoslof volcano, 53 nm northwest of Dutch Harbor, is currently 
active. 

A 1004 mb low 50 nm northwest of Nelson Lagoon dissipates by 
midday Friday. A strong front enters the northern Bering Fri 
morning...moves through the eastern Bering Fri night...then 
persists along the west coast of Alaska through Sat afternoon. 
High pressure builds across the central Bering on Sat.

$$

PKZ150-111230-
South of the AK Peninsula Sitkinak to Castle Cape-
343 PM AKDT Thu Aug 10 2017

.TONIGHT...S wind 15 kt. Seas 5 ft.
.FRI...S wind 15 kt. Seas 6 ft.
.FRI NIGHT...W wind 20 kt. Seas 5 ft.
.SAT...W wind 25 kt. Seas 7 ft.
.SAT NIGHT...W wind 20 kt. Seas 7 ft.
.SUN THROUGH MON...W wind 20 kt. Seas 8 ft.
.TUE...W wind 25 kt. Seas 10 ft.

$$

PKZ155-111230-
South of the AK Peninsula Castle Cape to Cape Sarichef-
343 PM AKDT Thu Aug 10 2017

.TONIGHT...SW wind 20 kt. Seas 6 ft.
.FRI...W wind 15 kt. Seas 5 ft.
.FRI NIGHT...W wind 20 kt. Seas 5 ft.
.SAT...W wind 25 kt. Seas 7 ft.
.SAT NIGHT...NW wind 20 kt. Seas 6 ft.
.SUN...E wind 15 kt. Seas 5 ft.
.MON...NW wind 20 kt. Seas 10 ft.
.TUE...W wind 25 kt. Seas 10 ft.

$$

PKZ160-111230-
Bristol Bay-
343 PM AKDT Thu Aug 10 2017

...SMALL CRAFT ADVISORY FRIDAY NIGHT...

.TONIGHT...SE wind 20 kt. Seas 4 ft.
.FRI...SE wind 15 kt becoming SW in the afternoon. Seas 3 ft.
.FRI NIGHT...W wind 15 kt becoming SW 25 kt after midnight. Seas
4 ft. Areas of fog. Rain.
.SAT...W wind 25 kt. Seas 7 ft.
.SAT NIGHT...W wind 30 kt. Seas 8 ft.
.SUN...NW wind 30 kt. Seas 8 ft.
.MON...N wind 15 kt. Seas 3 ft.
.TUE...NW wind 20 kt. Seas 3 ft.

$$

PKZ165-111230-
Port Heiden to Cape Sarichef-
343 PM AKDT Thu Aug 10 2017

...SMALL CRAFT ADVISORY FRIDAY NIGHT...

.TONIGHT...Variable wind 10 kt. Seas 3 ft.
.FRI...W wind 15 kt. Seas 3 ft.
.FRI NIGHT...W wind 15 kt increasing to 25 kt after midnight. Seas
5 ft. Patchy fog.
.SAT AND SAT NIGHT...NW wind 25 kt. Seas 7 ft.
.SUN...N wind 25 kt. Seas 7 ft.
.MON...N wind 20 kt. Seas 6 ft.
.TUE...NW wind 25 kt. Seas 5 ft.

$$

PKZ170-111230-
Cape Sarichef to Nikolski Bering Side-
343 PM AKDT Thu Aug 10 2017

.TONIGHT...W wind 15 kt. Seas 4 ft. Patchy fog.
.FRI...NW wind 15 kt. Seas 3 ft. Patchy fog.
.FRI NIGHT...W wind 20 kt. Seas 4 ft. Areas of fog.
.SAT...NW wind 20 kt. Seas 5 ft.
.SAT NIGHT...N wind 20 kt. Seas 6 ft.
.SUN...NE wind 25 kt. Seas 7 ft.
.MON THROUGH TUE...NW wind 20 kt. Seas 6 ft.

$$

PKZ171-111230-
Unalaska Bay-
343 PM AKDT Thu Aug 10 2017

.TONIGHT...NW wind 20 kt. Seas 3 ft. Patchy fog.
.FRI...NW wind 15 kt diminishing to 10 kt in the afternoon. Seas
3 ft. Patchy fog.
.FRI NIGHT...W wind 15 kt diminishing to 10 kt after midnight.
Seas 2 ft. Areas of fog.
.SAT...W wind 15 kt. Seas 3 ft.
.SAT NIGHT...NE wind 10 kt. Seas 3 ft.
.SUN...E wind 15 kt. Seas 3 ft.
.MON...N wind 15 kt. Seas 4 ft.
.TUE...NW wind 20 kt. Seas 4 ft.

$$

PKZ172-111230-
Cape Sarichef to Nikolski Pacific Side-
343 PM AKDT Thu Aug 10 2017

.TONIGHT...W wind 15 kt. Seas 5 ft. Patchy fog.
.FRI...NW wind 15 kt. Seas 5 ft. Patchy fog.
.FRI NIGHT...W wind 15 kt. Seas 5 ft. Patchy fog.
.SAT...W wind 15 kt. Seas 6 ft.
.SAT NIGHT...N wind 20 kt. Seas 5 ft.
.SUN...E wind 30 kt. Seas 8 ft.
.MON...NW wind 20 kt. Seas 10 ft.
.TUE...NW wind 25 kt. Seas 10 ft.

$$

PKZ173-111230-
Nikloski to Seguam Island Bering Side-
343 PM AKDT Thu Aug 10 2017

.TONIGHT...Variable wind 10 kt. Seas 4 ft. Patchy fog.
.FRI...Variable wind 10 kt. Seas 3 ft. Patchy fog.
.FRI NIGHT...Variable wind 10 kt. Seas 4 ft. Areas of fog.
.SAT...Variable wind 10 kt. Seas 4 ft.
.SAT NIGHT...NE wind 25 kt. Seas 7 ft.
.SUN...NE wind 30 kt. Seas 10 ft.
.MON THROUGH TUE...NW wind 20 kt. Seas 8 ft.

$$

PKZ174-111230-
Nikolski to Seguam Island Pacific Side-
343 PM AKDT Thu Aug 10 2017

.TONIGHT...Variable wind 10 kt. Seas 5 ft. Patchy fog.
.FRI...Variable wind 10 kt. Seas 4 ft. Patchy fog.
.FRI NIGHT...Variable wind 10 kt. Seas 5 ft. Areas of fog.
.SAT...NE wind 15 kt. Seas 5 ft.
.SAT NIGHT...E wind 30 kt. Seas 7 ft.
.SUN...E wind 30 kt. Seas 10 ft.
.MON THROUGH TUE...NW wind 20 kt. Seas 10 ft.

$$

PKZ175-111230-
Seguam Island to Adak Bering Side-
343 PM AKDT Thu Aug 10 2017

.TONIGHT...Variable wind 10 kt. Seas 3 ft. Patchy fog.
.FRI...Variable wind 10 kt. Seas 3 ft. Patchy fog.
.FRI NIGHT...Variable wind 10 kt. Seas 2 ft. Areas of fog.
.SAT...NE wind 15 kt. Seas 3 ft.
.SAT NIGHT...E wind 30 kt. Seas 7 ft.
.SUN...NE wind 30 kt. Seas 12 ft.
.MON...N wind 20 kt. Seas 10 ft.
.TUE...NW wind 15 kt. Seas 5 ft.

$$

PKZ176-111230-
Seguam Island to Adak Pacific Side-
343 PM AKDT Thu Aug 10 2017

.TONIGHT...NE wind 15 kt. Seas 5 ft. Patchy fog.
.FRI...NE wind 15 kt. Seas 4 ft. Patchy fog.
.FRI NIGHT...E wind 15 kt. Seas 5 ft. Areas of fog.
.SAT...E wind 25 kt. Seas 6 ft.
.SAT NIGHT...E wind 30 kt. Seas 10 ft.
.SUN...NE wind 35 kt. Seas 11 ft.
.MON...N wind 20 kt. Seas 11 ft.
.TUE...NW wind 15 kt. Seas 6 ft.

$$

PKZ177-111230-
Adak to Kiska-
343 PM AKDT Thu Aug 10 2017

.TONIGHT...NE wind 20 kt. Seas 5 ft. Patchy fog.
.FRI...NE wind 15 kt. Seas 5 ft. Areas of fog.
.FRI NIGHT...NE wind 20 kt. Seas 6 ft. Areas of fog.
.SAT...NE wind 25 kt. Seas 7 ft.
.SAT NIGHT...NE wind 30 kt. Seas 10 ft.
.SUN...NE wind 30 kt. Seas 13 ft.
.MON...N wind 20 kt. Seas 12 ft.
.TUE...W wind 15 kt. Seas 5 ft.

$$

PKZ178-111230-
Kiska to Attu-
343 PM AKDT Thu Aug 10 2017

.TONIGHT...NE wind 20 kt. Seas 6 ft. Areas of fog.
.FRI...NE wind 20 kt. Seas 5 ft. Areas of fog.
.FRI NIGHT...N wind 20 kt. Seas 5 ft. Areas of fog.
.SAT...N wind 20 kt. Seas 5 ft.
.SAT NIGHT...NE wind 25 kt. Seas 6 ft.
.SUN...NE wind 25 kt. Seas 9 ft.
.MON...NE wind 15 kt. Seas 10 ft.
.TUE...SW wind 15 kt. Seas 6 ft.

$$

PKZ179-111230-
Pribilof Islands Near Shore Waters-
343 PM AKDT Thu Aug 10 2017

.TONIGHT...Variable wind 10 kt. Seas 3 ft. Areas of fog.
.FRI...Variable wind 10 kt becoming W 20 kt in the afternoon. Seas
3 ft. Areas of fog.
.FRI NIGHT...W wind 20 kt. Seas 6 ft. Areas of fog.
.SAT AND SAT NIGHT...N wind 15 kt. Seas 7 ft.
.SUN THROUGH MON...N wind 20 kt. Seas 7 ft.
.TUE...NW wind 20 kt. Seas 6 ft.

$$

PKZ180-111230-
Kuskokwim Delta and Etolin Strait-
343 PM AKDT Thu Aug 10 2017

...SMALL CRAFT ADVISORY FRIDAY NIGHT...

.TONIGHT...NE wind 15 kt diminishing to 10 kt after midnight. Seas
4 ft.
.FRI...NW wind 10 kt becoming SW 20 kt in the afternoon. Seas 2
ft. Patchy fog.
.FRI NIGHT...W wind 30 kt. Seas 8 ft. Areas of fog.
.SAT...NW wind 30 kt. Seas 9 ft.
.SAT NIGHT...W wind 35 kt. Seas 10 ft.
.SUN...NW wind 30 kt. Seas 10 ft.
.MON THROUGH TUE...NW wind 20 kt. Seas 5 ft.

$$

PKZ181-111230-
North and West of Nunivak Island-
343 PM AKDT Thu Aug 10 2017

...GALE WARNING FRIDAY NIGHT...

.TONIGHT...Variable wind 10 kt. Seas 3 ft. Patchy fog.
.FRI...SW wind 25 kt. Seas 5 ft. Patchy fog.
.FRI NIGHT...NW wind 35 kt. Seas 12 ft.
.SAT...NW wind 35 kt. Seas 13 ft.
.SAT NIGHT...NW wind 40 kt. Seas 14 ft.
.SUN...N wind 30 kt. Seas 11 ft.
.MON THROUGH TUE...NW wind 20 kt. Seas 7 ft.

$$

PKZ185-111230-
Saint Matthew Island Waters-
343 PM AKDT Thu Aug 10 2017

...SMALL CRAFT ADVISORY THROUGH FRIDAY NIGHT...

.TONIGHT...W wind 25 kt. Seas 4 ft. Areas of fog.
.FRI...NW wind 30 kt. Seas 8 ft. Areas of fog.
.FRI NIGHT...N wind 30 kt. Seas 11 ft.
.SAT AND SAT NIGHT...NW wind 30 kt. Seas 11 ft.
.SUN...N wind 25 kt. Seas 9 ft.
.MON THROUGH TUE...NW wind 20 kt. Seas 6 ft.

$$

302 
FZAK52 PAFC 111200
CWFALU

Coastal Waters Forecast
National Weather Service Anchorage Alaska
400 AM AKDT Fri Aug 11 2017

Coastal Waters Forecast for Southwest Alaska+Bristol Bay+The
Alaska Peninsula Waters and the Aleutian Islands up to 100 nm out.

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.

PKZ199-120030-
400 AM AKDT Fri Aug 11 2017
.SYNOPSIS FOR SOUTHWEST ALASKA+BRISTOL BAY+THE ALASKA
PENINSULA WATERS AND THE ALEUTIAN ISLANDS...

Bogoslof volcano, 53 nm northwest of Dutch Harbor, is currently 
active. 

A 1005 mb low 45 nm west of Nelson Lagoon will dissipate this 
afternoon. A strong front will enter the northern Bering this 
afternoon and move to the eastern Bering tonight...then persist 
along the west coast through the Alaska Peninsula through Sat 
night. A second front will approach the Aleutians from the south 
Sat afternoon.

$$

PKZ150-120030-
South of the AK Peninsula Sitkinak to Castle Cape-
400 AM AKDT Fri Aug 11 2017

...SMALL CRAFT ADVISORY SATURDAY...

.TODAY...S wind 15 kt. Seas 6 ft.
.TONIGHT...W wind 20 kt. Seas 6 ft.
.SAT...W wind 25 kt. Seas 7 ft.
.SAT NIGHT...W wind 25 kt. Seas 7 ft.
.SUN...W wind 25 kt. Seas 7 ft.
.MON...Variable wind 10 kt. Seas 8 ft.
.TUE...W wind 20 kt. Seas 8 ft.

$$

PKZ155-120030-
South of the AK Peninsula Castle Cape to Cape Sarichef-
400 AM AKDT Fri Aug 11 2017

...SMALL CRAFT ADVISORY SATURDAY...

.TODAY...W wind 15 kt. Seas 5 ft.
.TONIGHT...W wind 20 kt. Seas 5 ft.
.SAT...W wind 25 kt. Seas 7 ft.
.SAT NIGHT...NW wind 20 kt. Seas 6 ft.
.SUN...NE wind 20 kt. Seas 5 ft.
.MON...NW wind 15 kt. Seas 8 ft.
.TUE...NW wind 20 kt. Seas 8 ft.

$$

PKZ160-120030-
Bristol Bay-
400 AM AKDT Fri Aug 11 2017

...SMALL CRAFT ADVISORY TONIGHT AND SATURDAY...

.TODAY...SE wind 15 kt becoming SW in the afternoon. Seas 2 ft.
.TONIGHT...W wind 15 kt becoming SW 25 kt after midnight. Seas 4
ft. Areas of fog. Rain.
.SAT...W wind 25 kt. Seas 7 ft. Areas of fog. Rain.
.SAT NIGHT...W wind 30 kt. Seas 9 ft.
.SUN...W wind 30 kt. Seas 11 ft.
.MON...NW wind 10 kt. Seas 2 ft.
.TUE...W wind 15 kt. Seas 3 ft.

$$

PKZ165-120030-
Port Heiden to Cape Sarichef-
400 AM AKDT Fri Aug 11 2017

...SMALL CRAFT ADVISORY TONIGHT AND SATURDAY...

.TODAY...W wind 15 kt. Seas 3 ft.
.TONIGHT...W wind 15 kt increasing to 25 kt after midnight. Seas
5 ft. Patchy fog.
.SAT...W wind 25 kt. Seas 7 ft. Areas of fog.
.SAT NIGHT...NW wind 25 kt. Seas 8 ft.
.SUN...N wind 25 kt. Seas 8 ft.
.MON...N wind 15 kt. Seas 5 ft.
.TUE...NW wind 20 kt. Seas 4 ft.

$$

PKZ170-120030-
Cape Sarichef to Nikolski Bering Side-
400 AM AKDT Fri Aug 11 2017

.TODAY...NW wind 15 kt. Seas 3 ft. Patchy fog.
.TONIGHT...W wind 20 kt. Seas 4 ft. Areas of fog.
.SAT...W wind 20 kt in the morning becoming variable 10 kt. Seas
5 ft. Areas of fog.
.SAT NIGHT...N wind 20 kt. Seas 6 ft.
.SUN...NE wind 25 kt. Seas 7 ft.
.MON...N wind 20 kt. Seas 6 ft.
.TUE...W wind 20 kt. Seas 5 ft.

$$

PKZ171-120030-
Unalaska Bay-
400 AM AKDT Fri Aug 11 2017

.TODAY...NW wind 15 kt diminishing to 10 kt in the afternoon. Seas
2 ft. Patchy fog.
.TONIGHT...W wind 15 kt diminishing to 10 kt after midnight. Seas
2 ft. Areas of fog.
.SAT...W wind 15 kt diminishing to 10 kt in the afternoon. Seas
3 ft. Areas of fog.
.SAT NIGHT...N wind 10 kt. Seas 3 ft.
.SUN...E wind 15 kt. Seas 3 ft.
.MON...N wind 10 kt. Seas 3 ft.
.TUE...NW wind 15 kt. Seas 3 ft.

$$

PKZ172-120030-
Cape Sarichef to Nikolski Pacific Side-
400 AM AKDT Fri Aug 11 2017

.TODAY...NW wind 15 kt. Seas 5 ft. Patchy fog.
.TONIGHT...W wind 15 kt. Seas 5 ft. Patchy fog.
.SAT...W wind 15 kt. Seas 5 ft. Patchy fog.
.SAT NIGHT...N wind 20 kt. Seas 5 ft.
.SUN...E wind 30 kt. Seas 9 ft.
.MON...N wind 20 kt. Seas 9 ft.
.TUE...NW wind 20 kt. Seas 8 ft.

$$

PKZ173-120030-
Nikloski to Seguam Island Bering Side-
400 AM AKDT Fri Aug 11 2017

.TODAY...Variable wind 10 kt. Seas 4 ft. Patchy fog.
.TONIGHT...Variable wind 10 kt. Seas 3 ft. Areas of fog.
.SAT...Variable wind 10 kt. Seas 4 ft. Areas of fog.
.SAT NIGHT...NE wind 25 kt. Seas 7 ft.
.SUN...NE wind 30 kt. Seas 10 ft.
.MON...N wind 25 kt. Seas 8 ft.
.TUE...W wind 15 kt. Seas 6 ft.

$$

PKZ174-120030-
Nikolski to Seguam Island Pacific Side-
400 AM AKDT Fri Aug 11 2017

.TODAY...Variable wind 10 kt. Seas 5 ft. Patchy fog.
.TONIGHT...Variable wind 10 kt. Seas 6 ft. Areas of fog.
.SAT...NE wind 15 kt. Seas 6 ft. Areas of fog.
.SAT NIGHT...E wind 25 kt. Seas 7 ft.
.SUN...E wind 30 kt. Seas 10 ft.
.MON...N wind 20 kt. Seas 10 ft.
.TUE...W wind 20 kt. Seas 8 ft.

$$

PKZ175-120030-
Seguam Island to Adak Bering Side-
400 AM AKDT Fri Aug 11 2017

.TODAY...Variable wind 10 kt. Seas 3 ft. Patchy fog.
.TONIGHT...Variable wind 10 kt. Seas 2 ft. Areas of fog.
.SAT...NE wind 15 kt. Seas 4 ft. Areas of fog.
.SAT NIGHT...E wind 25 kt. Seas 7 ft.
.SUN...NE wind 30 kt. Seas 11 ft.
.MON...N wind 25 kt. Seas 8 ft.
.TUE...W wind 15 kt. Seas 5 ft.

$$

PKZ176-120030-
Seguam Island to Adak Pacific Side-
400 AM AKDT Fri Aug 11 2017

...SMALL CRAFT ADVISORY SATURDAY...

.TODAY...NE wind 15 kt. Seas 5 ft. Patchy fog.
.TONIGHT...E wind 15 kt. Seas 6 ft. Areas of fog.
.SAT...E wind 25 kt. Seas 7 ft. Areas of fog.
.SAT NIGHT...E wind 30 kt. Seas 9 ft.
.SUN...E wind 30 kt. Seas 11 ft.
.MON...N wind 20 kt. Seas 9 ft.
.TUE...W wind 15 kt. Seas 7 ft.

$$

PKZ177-120030-
Adak to Kiska-
400 AM AKDT Fri Aug 11 2017

...SMALL CRAFT ADVISORY SATURDAY...

.TODAY...NE wind 15 kt. Seas 5 ft. Areas of fog.
.TONIGHT...NE wind 20 kt. Seas 6 ft. Areas of fog.
.SAT...NE wind 25 kt. Seas 7 ft. Areas of fog.
.SAT NIGHT...NE wind 30 kt. Seas 8 ft.
.SUN...NE wind 30 kt. Seas 10 ft.
.MON...N wind 20 kt. Seas 8 ft.
.TUE...NW wind 15 kt. Seas 5 ft.

$$

PKZ178-120030-
Kiska to Attu-
400 AM AKDT Fri Aug 11 2017

.TODAY...NE wind 20 kt. Seas 5 ft. Areas of fog.
.TONIGHT...N wind 20 kt. Seas 4 ft. Areas of fog.
.SAT...N wind 20 kt. Seas 5 ft. Patchy fog.
.SAT NIGHT...NE wind 20 kt. Seas 6 ft.
.SUN...NE wind 25 kt. Seas 7 ft.
.MON...NE wind 15 kt. Seas 6 ft.
.TUE...NW wind 15 kt. Seas 6 ft.

$$

PKZ179-120030-
Pribilof Islands Near Shore Waters-
400 AM AKDT Fri Aug 11 2017

...SMALL CRAFT ADVISORY SATURDAY...

.TODAY...Variable wind 10 kt becoming W 20 kt in the afternoon.
Seas 3 ft. Areas of fog.
.TONIGHT...W wind 20 kt. Seas 5 ft. Areas of fog.
.SAT...NW wind 15 kt. Seas 8 ft.
.SAT NIGHT...N wind 15 kt. Seas 8 ft.
.SUN THROUGH MON...N wind 15 kt. Seas 6 ft.
.TUE...W wind 15 kt. Seas 6 ft.

$$

PKZ180-120030-
Kuskokwim Delta and Etolin Strait-
400 AM AKDT Fri Aug 11 2017

...SMALL CRAFT ADVISORY TONIGHT AND SATURDAY...

.TODAY...NW wind 10 kt becoming SW 20 kt in the afternoon. Seas 3 
ft. Isolated thunderstorms in the afternoon. Patchy fog.
.TONIGHT...W wind 30 kt. Seas 7 ft. Areas of fog.
.SAT...NW wind 30 kt. Seas 10 ft.
.SAT NIGHT...W wind 35 kt. Seas 10 ft.
.SUN...NW wind 30 kt. Seas 9 ft.
.MON THROUGH TUE...NW wind 15 kt. Seas 4 ft.

$$

PKZ181-120030-
North and West of Nunivak Island-
400 AM AKDT Fri Aug 11 2017

...GALE WARNING TONIGHT AND SATURDAY...

.TODAY...SW wind 25 kt. Seas 5 ft. Patchy fog.
.TONIGHT...W wind 40 kt. Seas 13 ft.
.SAT...NW wind 40 kt. Seas 13 ft.
.SAT NIGHT...NW wind 40 kt. Seas 14 ft.
.SUN...NW wind 30 kt. Seas 10 ft.
.MON THROUGH TUE...NW wind 20 kt. Seas 6 ft.

$$

PKZ185-120030-
Saint Matthew Island Waters-
400 AM AKDT Fri Aug 11 2017

...GALE WARNING TONIGHT...

.TODAY...NW wind 30 kt. Seas 8 ft. Areas of fog.
.TONIGHT...N wind 35 kt E of Saint Matthew Island...N 30 kt W of
Saint Matthew Island. Seas 12 ft.
.SAT...N wind 30 kt. Seas 12 ft.
.SAT NIGHT...NW wind 30 kt. Seas 11 ft.
.SUN...N wind 25 kt. Seas 8 ft.
.MON...N wind 20 kt. Seas 6 ft.
.TUE...W wind 15 kt. Seas 6 ft.

$$

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
503 PM AKDT Wed Aug 9 2017

Updated aviation discussion

.ANALYSIS AND UPPER LEVELS...
A deep closed upper level low is centered south of the Alaska
Peninsula with a high amplitude trough extending southeastward
into the northeast Pacific. A strong vorticity-maximum which
rounded the base of the trough on Tuesday is now tracking
westward around the north side of the low center, dragging the
low and trough northward. Steady rain (heavy in places) is
falling from Kodiak Island north to the southern Kenai Peninsula
and along the south side of the Alaska Peninsula. Rain is
spreading over the Alaska Peninsula into Bristol Bay, though low
level southeast flow is limiting the amount and intensity of rain.

A strong downstream ridge over Southcentral is gradually being
pushed off to the north and east, though inland areas remain
fairly warm and dry with some sunshine - especially in the
Copper River Basin.

Out west, stable low levels continue to produce widespread low
clouds and fog. A closed vertically stacked low dropping south
across the central Aleutians is producing areas of rain from
Adak to Atka.

&&

.MODEL DISCUSSION...
The models remain on the same page with regard to handling of
the "big picture". However, the complexity of smaller scale waves
rounding the upper low center leads to a challenging precipitation
forecast. As would be expected, all of the models QPF fields are a
bit different. Thus, forecast confidence in the details of timing
and amounts of rain is low.

The forecast becomes more complicated Thursday night through
Friday night as the upper low begins to track east toward the Gulf,
with southerly flow out ahead of it bringing a steady stream of
upper waves northward toward Southcentral. Model spread is fairly
large with surface low/trough elongating over the Gulf, but there is
good agreement that rain will spread northward across portions of
Southcentral.

&&

.AVIATION...
PANC...Expect lowering ceilings and occasional rain this afternoon
and evening, though persistent low level southeast flow should
keep ceilings safely VFR. A more significant short-wave will move
through overnight tonight though early Thursday morning bringing
steadier and heavier rain. Do expect ceilings to drop below 5000
feet, but remain VFR. There may briefly be some lower ceilings in
the vicinity as rain saturates the low levels - most likely
between 12z and 18z Thursday.

Pressure gradient forecasts support the Turnagain wind remaining
close by West Anchorage through the evening hours. As a result there
is some question as to whether the gusty southeasterly winds that
have developed will be persistent this evening, or fade in and out.
If the wind does diminish it will likely continue just to the west
of the terminal through evening and impact approaches to the west.

 &&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Increased rain chances are expected into Saturday as low pressure
near the Alaska Peninsula tracks to the gulf this weekend. The
front currently along the Kenai begins to push north tonight as
the low near the peninsula slowly lifts to the Bering. Rain will
spread into Southcentral this evening and continue as steady rain
through early Thursday afternoon, then change to a showery
regime as the upper level wave associated with the front swings
north of the Alaska Range. Rain accumulations are expected to
average around one quarter of an inch with this front for inland
locations and along the western Kenai, with higher amounts between
one to two inches along the northeast gulf and Prince William
Sound coasts.

The main low near the peninsula shifts to the east on Thursday
night tracking across the southern gulf on Friday. This will keep
ongoing showers in the forecast across the region with the highest
accumulations focused along the northeastern gulf coast and
Prince William Sound.

The biggest challenge in the short range forecast is the
anticipated merger of the gulf low with a fast tracking arctic
low, which dives across the northwest coast on Friday. The gulf
system pumps plenty of gulf moisture inland ahead of this cold low
plunging south. A deformation band will likely set up along the
southern southern tier of the mainland with possible moderate to
heavy rain for Saturday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
An upper level closed low remains anchored over the Eastern
Aleutians, and is accompanied by shortwave rotating around this
synoptic feature. These shortwaves continue to push from the east
to west direction, and spreading rain showers through the
Southwest Alaska region through Friday morning. Then an upstream
arctic trough will be dropping down from the north off the Eastern
Siberian area before entering the Kuskokwim Delta by late Friday
evening. This feature brings cooler temperatures from the north as
the trough moves from west to east through the Southwest Alaska
region.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The eastern Bering has a low pressure system located just north
of Port Moller with an occluded weather front draped over the
Alaska Peninsula into the North Pacific Ocean this evening.
This system will continue to produce a showery regime over the
Eastern Aleutians/Bering before dissipating by Friday morning.
While the western Bering has a high pressure ridge extending into
the Central Aleutians/Bering through Friday. Therefore, look for
continued widespread marine layer stratus/fog as we head into the
weekend. Meanwhile, the northern Bering has a 998 mb low
developing by Friday morning. By Friday afternoon this low tracks
into the Norton Sound region accompanied by a cold front extending
through Hooper Bay southward into the central Bering. This system
brings gusty northerly winds to the northern Bering during the
aforementioned time-frame.

&&

.LONG TERM FORECAST (Days 3 through 7/ Saturday through Wednesday)...

On Saturday, an upper level low diving southward out of the Arctic
will move into Southwest Alaska. Widespread rain is expected over
much of mainland southern Alaska as a the cold air associated with
the low lifts the warmer air in place over the rest of
Southcentral. Thus, where precipitation ends up being most
concentrated, periods of heavy rainfall will be possible.

The model agreement with this feature is good on the large scale,
but differences in the timing, the depth of the trough, and any
embedded shortwaves still make pinpointing where the heaviest rain
will be a challenge to say the least. The instability in the
models has diminished with the feature, so any thunderstorm
potential now looks to be associated with any isolated cells
embedded within the broader precipitation shield.

By Sunday, the models once again diverge greatly regarding how the
pattern evolves. While the upper low over the Aleutians now no
longer appears to be a contributing factor in mainland
precipitation, the large disagreement with how quickly the upper
level low moves across Southcentral makes for a wide variation of
possibilities as to how the forecast evolves. The areas of
commonality include some degree of convective shower activity over
much of Southcentral...and a much cooler day as 850 mb
temperatures dip to near zero, with colder values over Southwest
Alaska.

Large disagreements in the models continue for Monday and beyond,
with very little that can be said definitively at this point.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

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