Heavy Freezing Spray Warning 40, NWS Anchorage, AK

022 
FZAK62 PAFC 181237
OFFALU

Offshore Waters Forecast
National Weather Service Anchorage AK
337 AM AKST Thu Feb 18 2021

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.

PKZ499-190200-
337 AM AKST Thu Feb 18 2021
.SYNOPSIS FOR CENTRAL BERING SEA...

A 957 mb low near Kamchatka moves to 52N 168E at 975 mb by Sat 
morning. A 980 mb low develops Fri morning near 54N 171W and 
moves to 56N 165W at 974 mb by Sat morning. Another low develops 
near 56N 157W by Sat morning. 

$$

PKZ411-190200-
Bering Sea Offshore West of 180 and East of the International
Dateline-
337 AM AKST Thu Feb 18 2021

...GALE WARNING THROUGH TONIGHT...

.TODAY...SE wind 25 to 40 kt. Seas 9 to 17 ft. Freezing spray N of
56N. Snow and rain.
.TONIGHT...S wind 25 to 40 kt. Seas 12 to 18 ft. Snow.
.FRI...S wind 10 to 25 kt. Seas 12 to 18 ft.
.FRI NIGHT...SE wind up to 20 kt. Seas 10 to 17 ft.
.SAT THROUGH MON...NE wind 15 to 30 kt. Seas 11 to 19 ft.

$$

PKZ412-190200-
Bering Sea Offshore 171W to 180 and North of 56N-
337 AM AKST Thu Feb 18 2021

...GALE WARNING TONIGHT AND FRIDAY...

.TODAY...NE wind up to 15 kt becoming E 15 to 30 kt in the
afternoon. Seas 3 to 8 ft. Freezing spray.
.TONIGHT...SE wind 25 to 40 kt. Seas 8 to 13 ft. Freezing spray.
Widespread snow showers.
.FRI...SE wind 25 to 40 kt. Seas 11 to 18 ft. Freezing spray.
Snow.
.FRI NIGHT...E wind 20 to 35 kt. Seas 11 to 18 ft.
.SAT THROUGH SUN...NE wind 15 to 30 kt. Seas 8 to 13 ft.
.MON...E wind 15 to 25 kt. Seas 6 to 11 ft.

$$

PKZ413-190200-
Bering Sea Offshore 171W to 180 and South of 56N-
337 AM AKST Thu Feb 18 2021

...GALE WARNING THROUGH TONIGHT...

.TODAY...S wind 10 to 25 kt becoming SE 20 to 35 kt in the
afternoon. Seas 5 to 10 ft.
.TONIGHT...S wind 25 to 40 kt. Seas 8 to 13 ft. Snow and rain.
.FRI...SW wind 10 to 20 kt. Seas 8 to 12 ft.
.FRI NIGHT...SW wind up to 20 kt. Seas 7 to 11 ft.
.SAT THROUGH SUN...E wind 10 to 25 kt. Seas 7 to 12 ft.
.MON...SE wind 15 to 30 kt. Seas 8 to 13 ft.

$$

PKZ414-190200-
Bering Sea Offshore East of 171W-
337 AM AKST Thu Feb 18 2021

...GALE WARNING FRIDAY...
...HEAVY FREEZING SPRAY WARNING TONIGHT AND FRIDAY...

.TODAY...NW wind 10 to 20 kt. Seas 4 ft. Freezing spray.
.TONIGHT...NE wind up to 20 kt becoming E 15 to 30 kt after
midnight. Seas 3 to 7 ft. Heavy freezing spray.
.FRI...E wind 20 to 35 kt. Seas 6 to 11 ft. Heavy freezing spray.
Widespread snow showers.
.FRI NIGHT...NE wind 20 to 35 kt. Seas 9 to 14 ft.
.SAT THROUGH SUN...NW wind 10 to 25 kt. Seas 6 to 11 ft.
.MON...SE wind 15 to 30 kt. Seas 5 to 9 ft.

$$

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
523 AM AKST Wed Feb 17 2021

.ANALYSIS AND UPPER LEVELS...

Snowfall that resulted in a few inches of accumulation across much
of the Mat-Su Valleys on Tuesday has now cleared out of
Southcentral this morning. A new band of snow and mixed
precipitation is working its way up the Kenai Peninsula as a
shortwave trough in the upstream portion of a ridge building over
the Gulf sweeps across the Northern AKPEN and approaches the
North Gulf Coast. Heavier rain/snow is moving into areas around
the Prince William Sound and eastern Kenai Peninsula as the wave
approaches, with increasing southeast flow out ahead. This
southeast flow is leading to downslope drying on the lee faces of
the Chugach and Kenai Mountains, and little to no snowfall is
making it to the surface at the moment across most of the Mat-Su
Valleys. The band of snow also extends across the Southwest, or
near and north of Bristol Bay, where visibilities have been
locally reduced down to 1 mile at times early this morning.

Farther out west, a vertically stacked low now near Unalaska
continues to slowly fill as it finally begins to pick up an
eastward pace. Winds around this low continue to die off and are
now down to small craft or lower across most of the Bering. The
low continues to have very minimal impacts apart from scattered
rain/snow showers within a broad expanse of low stratus spread
across the Bering around the finally departing system.

&&

.MODEL DISCUSSION...

Models are coming into much better agreement with large scale
features through the end of the workweek. The main point of
disagreement lies in the finer scale progression of a front moving
into the Gulf this morning. Models continue to stall out this
front and retrograde it back west into the central and western
Gulf as it falls under increasing influence from a deep low moving
up into the eastern Gulf by Thursday. The track and strength of
the Gulf low itself are coming into better alignment for Thursday
and Friday, but slight differences in the location of the remnant
front or inverted trough farther west continue to cause problems
with the forecast over Southcentral late tonight into Thursday.
Confidence is high that a deformation band of snow will develop
along an axis from the northern Gulf to somewhere near or over
Anchorage and along the Mat-Su Valleys by early Thursday. However,
even hi-res model guidance remains in disagreement for the exact
location and timing of this narrow band of snow on Thursday, and
this model discrepancy remains as the central forecast challenge
for this package.

&&

.AVIATION...
PANC...VFR conditions will persist through the early morning with
LLWS of about 30 kts continuing with the southeast winds above
ground level until about mid morning. A quick moving band of snow
may briefly impact the terminal before noon, potentially leading
to MVFR restrictions to visibility and ceiling. A very brief
period of IFR visibility with this snow cannot be ruled out before
snow clears the area by the afternoon and VFR conditions return.

By late tonight into early Thursday, the forecast becomes very
challenging, with models showing differing scenarios for the
development of a band of snow that will set up over or near the
Anchorage area. The TAF currently reflects the expectation for the
band of snow to directly impact PANC, with IFR snow beginning
early Thursday morning. However, due to the lingering uncertainty
with the timing and location of this round of snow, it remains
possible conditions will remain better than what is currently
reflected for portions of the end of the TAF period. This could
occur if the narrow axis of snow does not develop directly over
Anchorage, or if the timing of the snow is delayed, which remains
possible as of this writing.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3: Today
through Friday Afternoon)...

A frontal system moving north toward the Southcentral coast this
morning continues to produce snow from Seward to Whittier and
across Prince William Sound. Southeasterly gap winds are also on
the increase ahead of the front and are expected to peak from
Portage Valley to the Upper Hillside of Anchorage later this
morning as the front moves north. A weak inverted trough along
with a shortwave moving up Cook Inlet may act to mitigate the
downsloping that has taken place overnight across the western
Kenai Peninsula north to the Mat-Valley as the flow aloft shifts
from southeasterly to southwesterly. If it does, a brief period of
light snow is likely to develop from Kenai to Palmer with a
dusting to perhaps a half inch of accumulation. Snow accumulations
are expected to be a bit higher for the northern and western
Susitna Valley due to the southwesterly flow.

As the frontal system lifts north this morning, warmer air will
work in across Prince William Sound and the eastern Kenai
Peninsula. A transition to a mix of rain/snow, or potentially all
rain, is still possible for places like Seward, Whittier, and
Valdez by early afternoon. However, upwards of a foot of wet snow
is still expected for Whittier and Valdez before any change over
of precipitation.

By late Wednesday, a strong low will develop over the Northeast
Pacific and track toward then along the Alaska Panhandle. This
system will amplify a ridge along the coast and cause the current
system to begin to retrograde back to the west. An inverted trough
will develop to the northwest of the Northeast Pacific low which
will help enhance the precipitation shield as it moves toward the
Kenai Peninsula. By late Wednesday night, snow will again develop
over the Kenai Peninsula. The snow will then spread west across
Cook Inlet, the Anchorage Bowl, and Mat-Valley by early morning
Thursday. The snow will again transition to a rain/snow mix by
Thursday afternoon along the coast.

A general 2 to 3 inches of snow is expected from Kenai north to
Palmer before an advancing upper-level trough pushes this system
back to the east. However, there could be localized higher snow
amounts depending on the exact position of the inverted trough and
associated deformation band. An offshore flow will develop by
Friday as colder air works from the interior. Gusty outflow winds
are expected along the coast. Light snow will continue, however,
across the Copper River Basin through Friday as the upper-level
trough takes its time exiting the region.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Wednesday
through Friday)...

A front passes over the Southwest today as the persistent low that
has been lingering over the Aleutian Islands the past few days
finally begins moving east. Steady snowfall is expected across
parts of Bristol Bay and the Kuskokwim Valley through tonight.
Temperatures will begin to drop rather drastically starting
tonight as flow behind the low becomes northerly across the
Mainland and conditions begin to dry up and clear out. Clear skies
allow for radiational cooling, and by Thursday night temperatures
are expected to drop into the negative across the Kuskokwim Delta
and Kuskokwim Valley, and into the single digits/low teens for
Bristol Bay/AKPEN. Cold and clear conditions are expected to
persist through the end of the week.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3:
Wednesday through Friday)...

The persistent low that has been lingering over the Aleutian
Islands the past few days finally begins moving off to the east
today. Light precipitation will likely fall behind the low as a
rain/snow mix, becoming all snow by late tonight, once the flow
becomes primarily northwesterly across the Eastern Aleutians and
Southern AKPEN. There will be a brief break from rain and snow
Thursday afternoon before the next system arrives.

Further west, a front crosses the Western Aleutians, tracking
across the Bering through Thursday night and stalls over the
Pribilof Islands on Friday. As of right now, storm force winds are
not expected, but the possibly cannot be completely ruled out.
High end Gales at or above 40 kts (46 mph) are expected along the
front Thursday and Friday. Periods of moderate to heavy
precipitation are also expected across the Aleutian Islands as the
front passes, becoming light behind the front.

Heavy freezing spray will continue to be an issue across the
Northern Bering and will begin making its way farther down the
Southwest Coast on Thursday.

&&

.MARINE (Days 3 through 5: Friday through Sunday)...

Bering Sea: A gale force frontal system is expected to remain
fairly stationary across the northern Bering Sea south of Saint
Matthew Island for Friday. This front will then slowly weaken
Saturday and continuing into Sunday. Fairly quiet weather is
expected for the central and southern Bering with less than 35 kts
winds and less than 20ft seas. With the same pattern remaining in
place through the forecast period, heavy freezing spray will
continue to be an issue near the ice edge.

Gulf of Alaska: Small craft advisory level westerly winds are
expected for Friday with possibly gale force winds out of the
Barren Islands area. Seas are expected to be under 20 ft. A
stronger storm system with the potential for widespread gale force
winds and high seas greater than 20 ft may impact the Gulf of
Alaska sometime in the Saturday to Sunday time frame but
uncertainty remains in the exact details.

&&

.LONG TERM FORECAST (Days 3 through 7: Saturday through Tuesday)...

The long term forecast period pattern continues to resemble an
Arctic trough/low pressure extending from the Arctic Ocean
southwestward across much of the Alaska Mainland. With this strong
Arctic high in place, the jet stream is expected to remain
generally south of the Alaska Mainland over the North Pacific.
This will keep the storm track progressive from west to east
across the Aleutian Island Chain and through the southern Bering
keeping the weather active for those areas. For the Alaska
Mainland, cold air is expected to dominate much of the period as
the Arctic trough holds strong. This means much colder than normal
temperatures for this time period with outflow winds for
Southcentral. However, there continues to remain discrepancies on
the individual storms and subtle upper level shortwaves that may
try to come northward and bring some snow to Southcentral areas.
This will largely be determined by the strength of the Arctic
trough to the north. If it is stronger, it would most likely
suppress everything southward and keep the system offshore. If
the trough is weaker, some of these features might try to come
northward and bring some snow to Southcentral.

Towards the end of the forecast period going into Tuesday, there
are hints of a pattern change. Model guidance is showing the jet
stream coming further north (some guidance is more amplified than
other guidance) which would yield milder temperatures (closer to
normal) with the potential for an active storm track. The details
on each of these storm systems remains very uncertain.
Nevertheless, potential exists for a snowier and milder period
beginning around Tuesday next week. However, there remains a great
deal of variability with the pattern. Model guidance tends to
move things along too fast when indicating a pattern change,
therefore, stay tuned for the latest updates.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning: 119,175-178,411,413.
 		 Heavy Freezing Spray: 180,185,414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AS
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KM
MARINE/LONG TERM...MV