Gale Warning 443, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
411 PM AKDT Tue Aug 30 2022

.ANALYSIS AND UPPER LEVELS...

The pattern has begun to shift with a low near the Gulf of Anadyr
and a warm occluded front moving into the Kuskokwim Delta and
extending south towards the AKPen. This front is bringing rain and
stronger winds across the Bering Sea and Southwest Alaska.
Another strong shortwave is moving across the western Aleutians
producing rain. Across the east, the low over the Gulf of Alaska
the past few days is lifting northeast producing a few showers
near Prince William Sound. Fog was reported this morning across a
few spots in Bristol Bay and Southcentral, but it has since
dissipated. Otherwise, southwesterly flow is beginning to develop
over the Susitna Valley producing showers.

&&

.MODEL DISCUSSION...

Models are in good agreement with the synoptic pattern, however
the NAM has been a bit faster moving the precipitation and low
across the Gulf on Thursday. However, the latest NAM run is
coming into better agreement. The main forecast challenges will be
timing and strength of the southerly gap winds across Southcentral
as well as QPF amounts along the west side of the Chugach and
Kenai Mountains where low level downsloping affects look minimal
because of strong upper level dynamics and southerly flow in the
mid and upper levels.

&&

.AVIATION...

PANC...Gusty southeasterly winds look to persist all the way
through Wednesday thanks to a synoptic scale low sitting over the
northern Bering Sea. The strongest winds look to be overnight
tonight (between 09Z and 15Z) right ahead of an approaching front.
Winds will then slowly diminish Wednesday as a triple point low
develops over the northwest Gulf and shifts the pressure gradient
orientation. Strong dynamics aloft combined with deep moist
south-southwest flow aloft will bring in a solid area of steady
rain Wednesday morning. Despite the shallow southeasterly flow
expect at least brief periods of MVFR conditions as the heavier
rain moves through.

&&

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

Remnants of an upper level low in the Gulf of Alaska continue to
drive off to the southeast through tonight. Most of the impacts
from this system have diminished aside from a few lingering light
rain showers across the Valdez and Cordova areas.

A solid low pressure system over the northern Bering extends its
front across Southwest Alaska tonight, spilling over into
Southcentral on Wednesday. There is a strong moisture fetch along
the front, indicated well on satellite imagery, that will aid in
producing ample amounts of rainfall to Southcentral, especially
along the north Gulf coast, beginning late tonight. Winds through
Turnagain Arm and along the Copper River will start to ramp up
tonight and tomorrow, respectively, as the pressure gradient
between higher pressure moving across the Gulf tonight, and a
front moving across Southwest Alaska. A barrier jet forms along
the north Gulf coast early Thursday morning as the front pushes
against it. There is evidence of a possible downslope component as
upper level southeasterly flow becomes gusty late tonight into
Wednesday morning. As such there could be gaps in the rain showers
across Anchorage and western Kenai Peninsula. On the flip side,
there are a series of upper level waves passing through, which may
negate any possible downsloping at all. All in all, conditions
will be showery into the morning hours and any breaks in the
precipitation will be relatively brief. Showery conditions across
northern Susitna Valley that began early this morning, will not
only continue through Thursday, but will spread southwards to
encompass the rest of the Susitna Valley tonight, and then into
the Mat Valley Wednesday morning. The bulk of the rainfall and the
highest rain rates will be across Prince William Sound and along
the north Gulf coast, as is typical in this type of pattern.
Additionally, rainfall will spill into parts of the Copper River
Basin, mainly confined to the higher elevations while the valleys
remain relatively dry.

As the front pushes inland on Thursday, winds across Southcentral,
and the barrier jet winds should start to diminish.

&&

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

The wet, early fall pattern has returned on schedule, and it does
not look likely to change back to summer anytime soon. In the
near term, a front will continue to move inland overnight, sending
bands of rain and gusty southerly winds across as it begins to
shear apart and move across the western Alaska Range towards
Southcentral by early Wednesday. Behind this weakening front,
strong southwesterly flow will become established as a large area
of cyclonic flow spreads over the Bering in association with a
deep low moving east out of the Kamchatka Peninsula. A series of
shortwaves will rotate around the main upper center into Southwest
through Thursday, the strongest of which arriving by early
Wednesday morning. This first wave will send a period of notably
intense, moderate rainfall across nearly the whole outlook area
on Wednesday, mainly during the morning hours.

Looking further out towards Thursday, the overall outlook does
not really get any warmer or drier. The center of the occluded,
stacked low over the northern Bering will advance southeast with
time, reaching the Kuskokwim Delta by Thursday afternoon. Periods
of light rain will continue across most of Southwest as waves of
energy continues to pinwheel inland from the Bering around the
low, but nothing as heavy as what we're likely to see Wednesday.
Gusty onshore, southwesterly winds will continue all day Thursday,
with the strongest winds focused along coastal areas.

By Friday, there should be a chance for at least the eastern parts
of the outlook area to dry out and warm up a bit, as the low
pushes farther south into the AKPen and allows the southwesterly
flow to flip to a more easterly orientation with time. There may
even be a few peeks of sun returning for a few spots across the
Lower Kuskokwim Valley and Bristol Bay. However, expect any
periods of sun to be interwoven with rain from passing showers,
particularly during the afternoon. This continued shower activity
will stem from overall unstable profile developing under the cool
upper level low as the surface heats up to near 60F Friday
afternoon.

&&

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

A relatively steady-state (but still unsettled) pattern will
remain in place across the Bering Sea for the next few days.
A large, stacked low will have the predominant influence over
virtually the entire outlook area as it drifts into the northern
Bering and then into Southwest between now and Friday. Brisk,
cyclonic flow near both the surface and aloft will spread across
the Bering and along the Aleutians between now and Thursday. This
should keep the strongest west to northwest winds at a steady 20
to 30 kts along most Bering-side coasts along much of the Aleutian
Chain and southern AKPen. Similarly strong winds around 30 kts
will continue up north across the Pribilofs from tonight all the
way into Friday. In the meantime up through Wednesday, a shortwave
trough will rapidly progress east along the low's occluded front
sagging across the Aleutians, aggravating steady rain along the
front until it crosses into the Pacific late on Wednesday morning.

From Thursday into Friday, a shortwave ridge should begin to
build across the western Bering, allowing winds to drop out along
the western Aleutians and possibly encouraging some clearing out
of low stratus along the western Aleutians. At least, until,
another frontal system approaches from the North Pacific with
increasing southeast winds, cloud cover and rainfall by Friday
afternoon. Strong, gusty winds shifting to a more northerly
direction will continue to the east along the eastern Aleutians
and southern AKPen for Friday as the low finally exits into the
Pacific west of Kodiak Island.

&&

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

Gulf of Alaska: Forecast confidence remains above average during
the 3-5 day period. The odds tilt in favor of gale force winds
along the northern Gulf of Alaska from Friday afternoon through
Saturday morning as the synoptic scale pattern will be favorable
for the development of a barrier-jet. Winds will then ease
Saturday afternoon as pressure gradients ease. Winds are then
expected to remain below gale force for the remainder of the
period. No high seas are expected.

Aleutians/Bering: Forecast confidence is above average for the
3-5 day period. There is a chance for gale force gap winds and
gusts through the eastern Aleutians and western Alaska Peninsula
Friday and Saturday. Otherwise, winds will remain below gale force
with no high seas expected.

&&

.LONG TERM FORECAST (Days 4 through 7: Saturday through Tuesday)...

The odds tilt in favor for below normal temperatures and above
normal precipitation for the days 4-7 period as an upper level
low remains nearly stationary over the northern Gulf and across
Southcentral Alaska. A surface low associated with the upper-low
is expected to move from the Gulf over Southcentral on Saturday.
This low is expected to bring rain across much of Southcentral.
Confidence is low with respect to actual precipitation amounts
across the area. Confidence is also low with respect to how much
precipitation reaches Southwest Alaska as the low moves inland.
The bulk of the precipitation is expected on Saturday, though
showers will linger through Tuesday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 119.
FIRE WEATHER...NONE.

&&

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