Gale Warning 300, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
535 AM AKDT Wed Apr 13 2022

.ANALYSIS AND UPPER LEVELS...
There is an omega block in place over mainland Alaska. The ridge
axis bisects Southcentral and there is a closed low over SE AK and
over the western/central Aleutians. There is a jet near Kamchatka
and the Western Aleutians with a magnitude of 170 knots. There is
a 997 mb low north of Attu and a 1002 mb low south of Attu. The
remnants of a frontal boundary are moving into western Alaska and
showers have been detected at the Bethel and King Salmon radars
over night. In the West Pacific Basin Typhoon Malakas is inching
its way closer to Japan and is on track to recurve towards the
Western Aleutians.

&&

.MODEL DISCUSSION...
The run to run continuity with the models has improved. The models
continue to bring a major low into the Bering on Thursday and
Friday. By 00z Friday the ECMWF and the Canadian bring the surface
low further to the north while the GFS and the NAM take a more
southerly track. This will impact where the gale and storm force
winds set up. Another forecast challenge will be the
precipitation type. The models show a rain/snow mix for most of
the region with snow in the wake of the front and pockets of rain
in the warm sector.

&&

.AVIATION...

PANC...VFR conditions and light winds will persist.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3;
Wednesday through Friday night)...

A blocking ridge over Southcentral will remain in place before
beginning to break down late Thursday into Friday. Marine stratus
around Kodiak Island yesterday has expanded in coverage to include
the northern Gulf; the southern coastline of the Kenai Peninsula,
including Seward; and along the Sterling Highway from Anchor Point
to Clam Gulch this morning. The extent of this cloud cover will,
once again, be the biggest forecast challenge through the next 24
to 36 hours. Right now, it looks like the bulk of the stratus will
remain over the coastal waters, with any cloud cover over coastal
locations this morning diminishing as temperatures rise after
sunrise. Higher clouds will also overspread interior Southcentral
as a weak upper-level wave rotates overtop the ridge.

As the ridge begins to break down, a frontal system will approach
the western Gulf and Kodiak Island with precipitation and gusty
southerly winds developing by Friday morning. Colder air aloft
will also advect across the northern Gulf in the wake of the
retreating ridge. Instability along the northern Gulf will
increase in response to the change in airmass. The increased lapse
rates from the colder air aloft, coupled with an increasing
southerly flow, will allow showers to develop along the
Southcentral coast by Friday afternoon out ahead of the main
frontal system. The front then stalls just south of the Barren
Islands for Saturday as showers linger across Prince William
Sound.

&&

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

The dominate upper-level ridge that has been sitting over
mainland Alaska for the past couple days, has begun to shift
eastward. This is allowing southerly/southeasterly winds to usher
clouds, gusty winds, and precipitation over Southwest Alaska. A
front associated with a low located in the western Bering, is
tracking towards Bristol Bay and the Kuskokwim Delta, however, it
is weakening due the ridge staying in place. With pressure
gradients tightening, due to the ridge staying in place and the
front pushing into the ridge, gusty winds are expected along the
Southwest coast early this morning through today. However, these
winds will gradually diminish throughout the day. Expected
downsloping areas will likely not see any precipitation with this
frontal passage, however, an isolated shower is not completely
ruled out. Upslope areas will receive the brunt end of
precipitation from this event.

Another front, associated with a much stronger Bering Sea low,
will be able to push further inland Thursday evening into Friday
as the ridge continues to shift east. This event will be very
similar to what will occur today in regards to winds increasing
due to pressure gradients tightening and downsloping and upsloping
occurring. However, winds will be much stronger with this frontal
passage. Gale force winds are expected along the immediate
coastal regions with storm force gusts, especially north of Cape
Newenham to Nunivak Island.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS/ALASKA PENINSULA (Days
1 and 3: Today through Friday night)...

The synoptic setup remains the same with an upper-level ridge
anchored over Southern Alaska and an upper-level trough in place
over the Bering Sea. A low currently located in the western
Aleutians will continue to slowly weaken through today and
gradually merge with a much stronger low pressure system rounding
the base of the trough this evening into tonight. Its associated
front is slowly tracking eastward this morning and will run into
the strong upper-level ridge located over mainland Alaska. Mostly
small craft winds with localized areas of gales, especially
through the gaps and passes areas along the Alaska Peninsula, are
expected today in association with the aforementioned frontal
passage. Some light precipitation may accompany the front, but
with deep southeasterly flow, expect the typical areas to
downslope with most, if any, precipitation confined to the
upslope areas of the Alaska Peninsula and Bristol Bay. However, an
isolated shower cannot be ruled out for areas west of Bethel and
for communities such as Nelson Lagoon, Port Heiden, and Pilot
Point.

As the aforementioned low merges with the other system rounding
the base of the trough this evening, the newly combined system
quickly strengthens through Thursday afternoon. As a result,
southeasterly gale force winds with storm force wind gusts are
expected as the front tracks east along the Aleutians and Alaska
Peninsula. Seas of 15 to 20 ft are also expected due to the
strong winds moving through the area. As the aforementioned front
passes through, it will be accompanied by a steady band of
moderate to potentially heavy precipitation. While most of the
Chain and Alaska Peninsula will be rain, the Pribilofs are on the
edge of being cold enough for snow, so a rain/snow mix is
possible. Expect westerly flow on the backside of the low with a
return to colder conditions and occasional rain and snow showers.
These showers may briefly lower visibility intermittently.

&&
.Marine (Days 3 through 5: Friday through Sunday)...
Gulf of Alaska: Prevailing high pressure over the Gulf will begin
to break down Friday night as a large low over the entire Bering
swings a front into the western Gulf. South to southeasterly
winds around 20 to 25 kts with gusts possible up to 35 kts in the
Kodiak area is about all this front will produce. Seas will
gradually increase Friday through Saturday up to 10 to 12 ft.

Bering Sea: A large low over the Bering Sea will remain through
the end of the week and will gradually weaken over the weekend as
a deeper low approaches the western extent of the Aleutians and
moves eastward Sunday. Exact timing and when it progresses
eastward is a little more unclear. Gales near St Matthew on Friday
and also in the southern Bering which will diminish Saturday and
then increase again on Sunday with storm force potential in the
southern Bering. Seas up to 15 ft possible.

&&

.Long Term Discussion (Days 4 through 7: Saturday through Tuesday)...

A low over the Bering sea will persist until this weekend and then
gradually weaken. The associated trough will stretch into the
western Gulf into Saturday and develop into a separate low
Saturday afternoon. This will work to weaken the prevailing high
pressure ridge over the Gulf and press it inland and eastward.
Confidence on the trajectory of this developing low remains lower
and may either continue towards the Pacific Northwest or will
remain in the southern Gulf or Northern eastern Pacific as a broad
low with multiple circulations of vorticity. Further west, a more
progressive pattern with the low over the Bering will gradually
weaken and a relatively deeper low will approach the western
extent of the Aleutians and move eastward along the length of the
Chain at the beginning of next week. Mixed precipitation along
with strong southerly winds with gales to storm force potential
through the Islands including the Pribilofs will be possible as
this low transits east going into the week ahead. The wrap around
return of strong northerly winds and continual precipitation will
pose a challenge to precipitation type and the subsequent
reductions in visibility. Towards midweek, this low continues into
the Gulf and a ridge will build behind for the west and central
Aleutians before another low approaches closely behind.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale 414 155 160 165 170 171 172 173 174 175 176 177 179
180 181.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...NS
MARINE/LONG TERM...VR