Gale Warning 420, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
624 AM AKDT Thu Aug 27 2020

.ANALYSIS AND UPPER LEVELS...

A 120 kt upper level jet extending from the Sea of Okhotsk into
the North Pacific is leading to the intensification of an upper
level low near the western Aleutians. This is likewise
strengthening the surface low and associated front as it tracks
across the Chain. Southerly gale force winds and moderate rain are
likely. An upper ridge remains in place over the central
Bering/Aleutians with the usual patchy fog/low stratus
accompanying it, but is otherwise quiet there. Farther east, a
large upper low is centered just south of Kodiak Island. It is not
deepening as the upper jet core is well to the south, however its
series of shortwaves in conjunction with the surface low will
continue to bring rain along the Gulf Coast today. Downsloped
areas and locations farther north away from higher terrain should
remain mostly dry.

&&

.MODEL DISCUSSION...

Models remain in good synoptic agreement. Timing of upper level
shortwaves will be pertinent to the precipitation timing and
amounts today. However, much of it should stay confined to the
Gulf and be minimally impactful. Ridging remains expected across
Southcentral Friday into Saturday. Difference still exist with
deep low approaching western Alaska this weekend. The latest GFS
has taken the track farther south, aligning with the ECMWF over
Bristol Bay.

&&

.AVIATION...

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

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...

A low over the Gulf keeps much of the Gulf coastal regions wet
for one more day. The remainder of Southcentral will begin to
dry out, with just some isolated to scattered showers lingering
through this evening. By Friday, the low makes its way towards the
Southeast Alaska coast, setting up an east-west oriented trough
along the Southcentral coast. Due to this pressure gradient,
gusty conditions can be expected for Whittier and Passage Canal,
as well as Seward and Resurrection Bay. Broad offshore flow
across Southcentral will lead to warmer temperatures, mostly dry
conditions, and even some sunshine. This will be a brief respite
from rain, as a strong front tracks to Kodiak Saturday and up to
Southcentral by Saturday night.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Thursday
through Saturday)...

Some showers continue to linger in Southwest Alaska, circulating
around the backside of low pressure that is now centered just
south of Kodiak Island. As this low continues to move slowly away
from Southwest AK, we can expect most showers to clear out. Enough
instability remains where showers will likely fire over areas of
elevated terrain and the Y-K Delta. Ridging responsible for this
break in the weather is only transitory, moving in from the
Eastern Bering and exiting on Saturday. The next round of weather
arrives Saturday on the heels of this ridge in the form a front
moving in from the Eastern Bering. This means rain and increased
winds for Southwest AK over the weekend.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3:
Thursday through Saturday)...

Low pressure has exited to the east, clearing out the showers that
were in the Eastern Bering/Aleutians. The shortwave ridge has
moved into the Eastern Bering. While this ridge will provide a
break in precipitation, we are still expecting low stratus and
fog under the ridge. This ridge is also quick moving in nature and
should exit late tomorrow. Satellite shows the next system now
entering the Western Aleutians. The low center doesn't move east
much, but its associated front can be expected to move across the
Bering/Aleutians the next few days. It will bring rain and weak
gale force winds as it goes.

&&

.MARINE (Days 3 through 5/Saturday through Monday)...

A North Pacific low moves across the Aleutians through Saturday.
Model confidence during this timeframe has remained consistent and
gale force winds are expected along the front in the eastern
Bering/Aleutians. Confidence begins to waiver Sunday morning. This
complex system spins up another low somewhere between 957 and 968
mb. Depending on the strength of this low will determine if winds
could potentially reach storm force or even hurricane force per
some guidance. As of now, high end gales are being forecasted.
Placement varies from over Dutch Harbor to just south of Saint
Paul with various locations in between not outside the realm of
possibility. The track of this storm through Monday remains highly
variable landing somewhere between the northeastern Bering or
crossing the Alaska Peninsula. All in all, there will be plenty
of refinement associated with this system as we go through the
week, but mariners in the area should pay close attention.

For the Western Gulf, timing of a front associated with a low
over the Aleutians is in better agreement today, expected Saturday
morning. Confidence is limited in regards to strength and
progression across the Gulf. Small craft to gale force winds are
possible as it propagates towards Prince William Sound late
Saturday into Sunday. Behind this front, confidence is reduced as
the track of the low, and it's strength, remain in question. If
the storm tracks across the Alaska Peninsula, it could bring up to
storm force winds into the Gulf Monday.

&&

.LONG TERM FORECAST (Days 4 through 7/Sunday through Tuesday)...

A large area of low pressure is forecast to develop in the Bering
Sea on Sunday as the energy from the post-tropical remnants of
Typhoon Bavi merge with a weak upper level low in the Bering Sea.
There is a high degree of uncertainty in the exact placement and
track of this low. However, there is a high confidence that high
end gale force winds are to be expected with a moderate confidence
of storm force winds south of the low center.

Due to the high uncertainty of the track of this low, an ensemble
forecast methodology was used with blending the ECMWF/GFS/GEM
solutions.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gales 177 178 411 413.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AP
SOUTHCENTRAL ALASKA...KM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BB
MARINE/LONG TERM...CK/EJD