Gale Warning 349, NWS Anchorage, AK

546 
FZAK61 PAFC 032323
OFFAER

Offshore Waters Forecast
National Weather Service Anchorage AK
323 PM AKDT Thu May 3 2018

Offshore waters forecast for the Gulf of Alaska West of 144W

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.

PKZ399-041330-
323 PM AKDT Thu May 3 2018
.SYNOPSIS FOR THE WESTERN GULF OF ALASKA...
A front in the western Gulf reaches the northeastern Gulf Fri 
afternoon. A complex 988 mb low at 52N 163W moves to 56N 158W at 
974 mb tonight then it will move inland Fri afternoon at 973 mb. 
The associated front remains nearly stationary across the central 
Gulf through Sat afternoon.

$$

PKZ351-041330-
Gulf of Alaska Offshore North of 57N and West of 144W-
323 PM AKDT Thu May 3 2018

.TONIGHT...S wind 20 to 30 kt. Seas 8 ft. Rain.
.FRI...S wind 30 kt. Seas 9 to 14 ft. Rain.
.FRI NIGHT...S wind 15 to 25 kt. Seas 13 ft.
.SAT...S wind 15 to 25 kt. Seas 11 ft.
.SAT NIGHT...SW wind 10 to 20 kt. Seas 8 to 11 ft.
.SUN THROUGH MON...SE wind up to 20 kt. Seas 5 to 9 ft.
.TUE...SE wind 25 kt. Seas 8 to 13 ft.

$$

PKZ352-041330-
Gulf of Alaska Offshore South of 57N North of 55N and West of
144W-
323 PM AKDT Thu May 3 2018

...GALE WARNING THROUGH FRIDAY...

.TONIGHT...S wind 20 to 35 kt. Seas 8 to 13 ft. Rain.
.FRI...S wind 20 to 35 kt. Seas 9 to 16 ft. Rain.
.FRI NIGHT...S wind 15 to 30 kt. Seas 11 to 14 ft.
.SAT...SW wind 10 to 25 kt. Seas 11 ft.
.SAT NIGHT...SW wind up to 20 kt. Seas 7 to 11 ft.
.SUN THROUGH MON...SE wind 10 to 25 kt. Seas 4 to 8 ft.
.TUE...SE wind 15 to 25 kt. Seas 9 to 14 ft.

$$

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
459 PM AKDT Wed May 2 2018

.ANALYSIS AND UPPER LEVELS...
The upper level shortwave that brought a round of late season
snowfall to the Matanuska Valley eastward into the Copper River
Basin and Thompson Pass areas overnight continues to slowly move
off to the east and dissipate. An area of weak high pressure
behind this shortwave brought a brief period of sunny skies to
Southcentral this morning, however this quickly filled in as
diurnal convection from the Kenai Peninsula spreads northward
towards the Anchorage Bowl. This area of convection even produced
some very small hail near the Soldotna area late this morning as
showers fell through low freezing levels. Further west over
Southwest Mainland this high pressure was too weak to provide much
relief from the stratus and areas of snow that developed,
allowing for widespread cloud cover to continue into this
afternoon. This is quickly beginning to fill in as the next
system approaches from the Eastern Bering. This low will be the
focus not only for another round of rain/snow and gusty easterly
winds for the Southwest Mainland, but also for a developing
triple point low that will develop in the Gulf on Thursday.

&&

.MODEL DISCUSSION...
The models remain in generally good synoptic scale agreement
through Thursday with the Eastern Bering low as it develops a
triple point low near the AKPen this evening. Ahead of this low,
none of the model guidance has handled the early diurnal convection
that has occurred over Southcentral well, as even the high
resolution models held off until late this afternoon to bring any
showers into the area. Afterwards there remains some uncertainty
in the low track and intensity of the low that will rapidly
develop under the Bering low and enter the Southwest Mainland for
Friday. The GFS in particular continues to be an outlier by
producing a deeper and further west position as the low makes
landfall late Friday. Since the GFS has been one of more variable
models with this system as it had previously been much further
east and deeper, this was treated as an outlier in favor of the
more consistent NAM and EC.

&&

.AVIATION...
PANC...The first question for early this evening will be for the
possible development of convective rain showers around the
terminal not only along the mountains be also around Cook Inlet as
showers from the Kenai Peninsula move northward. These should
generally be light and spotty with VFR conditions expected. Winds
will also shift to southeasterly and gust to around 20 kt this
evening as the gradient through Turnagain Arm increases.
Afterwards VFR conditions with light southeast winds are expected
into Thursday.

&&

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

A pattern shift in the upper level jet stream sets an active wet
and windy pattern into motion for the end of the week. The main
challenge in the forecast is focused around a storm system which
pushes across the Gulf on Thursday and then northward through
Southcentral Thursday night through Friday evening. Precipitation
with this storm system is primarily forecast as rain; however,
higher elevations over 1500 feet will stay cold enough to see all
snow and cooler locations inland changes over to light snow
during the night and early morning hours.

Gusty southeasterly winds and rain develop along the front which
is expected to move across Kodiak Island late this evening. The
frontal boundary moves quickly north making it to the Kenai and
north gulf coast by Thursday morning. The highest accumulations
are expected along the coast as abundant subtropical moisture
advects toward the southern mainland with the jet stream orienting
south to north as it noses along the Kenai on Friday. The jet
nudges toward the Alaska range into the the evening bringing the
best chance for accumulating rain across inland locations.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A frontal system currently centered over the Pribilof Islands will
move east tonight and spread precipitation across the coast and up
the Kuskokwim River Valley tomorrow. Easterly winds will increase
tonight and tomorrow as the front lifts northward with the highest
gusts seen through the Kamishak Gap and across Lake Iliamna.

The system will retrograde back to the south Thursday night as a
vigorous upper level low drops south across the Aleutians,
swinging around the old low while spinning up a strong surface
low. This low will be supported by a stout southerly upper level
jet which will send the system north across the AKPEN and into the
Bristol Bay area by Friday afternoon. A long southerly fetch of
wind and moisture will slam into the southern AKPEN coast and will
spread across the SW interior. Rain will be focused over the
Bristol Bay area and the Kuskokwim River Valley Friday morning
before spreading north and west into the Kuskokwim Delta by the
afternoon. Warm air associated with this system will keep freezing
levels higher so precipitation should stay all rain for most
lower elevation sites. Another round of gusty winds across the
western side of the Alaska and Aleutian Ranges are also expected
with this system, with the strongest gusts seen through the
Kamishak Gap and across Lake Iliamna.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A series of low pressure systems will impact the eastern Bering
and Aleutian Island chain bringing strong winds and precipitation
to the area through the end of the week. The strongest low will
form south of Cold Bay Thursday evening and rapidly strengthen as
it moves north. Cold air wrapping around the backside of the low
combined with a tightening pressure gradient will lead to a
a narrow band of northerly gale force winds developing from the
Pribilofs south to Dutch Harbor Thursday night through Friday
evening. Conditions will be a bit quieter for the western half of
the Bering though cold northerly flow will lead to some snow
showers developing between Adak and Dutch Harbor through the end
of the week.

&&

.LONG TERM FORECAST (Days 3 through 7...Sat through Wed)...
The weekend will start out with yet another strong low pressure
system moving inland. This system will bring strong winds, heavy
rain, and even the chance for heavy snow for higher elevations.
The low pressure center at the surface will drive from south to
north across SW AK early Sat morning. This will bring strong winds
to parts of Kodiak Island, into Bristol Bay, and along the Gulf of
AK coastline. The difference with this system from yesterday is
that it does not hold together and move far enough north to spread
much of these winds inland across Southcentral and Cook Inlet.

This system will be interesting in how far south it taps into
moisture. The fetch will extend all the way down to nearly 30N.
This is known as an atmospheric river. And at least to start the
weekend, it will be pointed at the Gulf Coast. The heaviest
precipitation does slide slightly east late Sat, but is quickly
reinforced along the coast by another shortwave moving into the
area early Sun. This heavy precipitation will work in tandem with
some cold air that filters into this system to provide some snow
for the higher elevations such as Thompson Pass. Being that it is
early May, it becomes harder and harder to get significant
snowfall, but certainly not impossible. There are many variables
that need to come together to keep the precipitation from turning
over to rain, but we have introduced a healthy (5-10") of snow to
the coastal mountains with this package.

By Sun and Mon, the pattern starts to show two main features: a
building North American Ridge and a very broad, unseasonably deep
low over the Central Aleutians. The ridge will try to build up
from SE AK, but as it does so, it ushers in another shot of
moderate rain and wind for Prince William Sound and areas east.
By the middle of next week, all models are in fairly good
agreement that the Aleutian low will slide very near the Cold Bay
area. The trend has been to take this low slightly further south
and try to build some weak ridging over the mainland from the
Yukon Territory. However, for now, it looks to continue to be
mostly cloudy and slightly warmer for Southcentral with continued
wet along the Gulf Coast.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Watch 155. Flood Advisory 152.
MARINE...Gale 132 150 155 170 172 173 174 179.

&&

SYNOPSIS AND MODEL DISCUSSION...DEK
SOUTHCENTRAL ALASKA...KH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KVP
LONG TERM...MSO