Gale Warning 442, NWS Anchorage, AK

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

.ANALYSIS AND UPPER LEVELS...

A low is developing near the Gulf of Anadyr and a series of
fronts extending from this low are pushing the ridge eastward
across the Bering Sea. The ridge is flattening across the area
where westerly winds along zonal flow to 30 kts is occurring
across much of the western Bering Sea. Radar echos are appearing
on the Bethel radar with the frontal boundary approaching the
Southwest coast. Towards Southcentral is a broad, high amplitude
trough. Easterly waves into the area has brought showers and a few
isolated thunderstorms over the previous afternoon and evening.
Radar reflectivity still indicates some showers are occurring
along the Gulf coast and north through the Susitna Valley. Similar
to the previous few days, patchy fog and low stratus are
occurring for some areas that had received showers during the
day, followed by skies clearing after dark to promote radiational
cooling at the surface.

&&

.MODEL DISCUSSION...

Synoptically, models are continuing to be in good agreement as
the next system moves across the northern Bering and a couple of
frontal passages moves across Southern Alaska through the rest of
this week. Very subtle differences exist with the timing of each
of wave, not only for Southcentral, but also on the back side of
the low across the Central Aleutians Thursday night. As the low
moves into the western Gulf, consensus with the models begins to
shift. However, the overall picture remains in reasonably good
agreement going through the weekend.

&&

.AVIATION...

PANC...Expect VFR conditions. Fog potential may return to the
terminal Tuesday morning. Winds will increase through Turnagain
Arm and Cook Inlet into Tuesday morning and could bend into PANC
beginning Tuesday afternoon. Gusty winds up to 30 kts is possible
at the airport and should peak after midnight into Wednesday
morning.

&&
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3 -
Tuesday through Thursday night)...

An upper-level low over the eastern Gulf of Alaska this morning
will slowly drift to the Alaska Panhandle by Wednesday morning.
A series of upper-level waves continues to rotate around the low,
with the strongest of these features producing a inverted trough
moving west toward Middleton Island this morning. This feature is
producing an area of scattered showers from Cordova to western
Prince William Sound. These showers will continue through the
early afternoon before diminishing as the aforementioned low
moves east. A few areas of fog have also formed again during the
early morning hours, especially along Cook Inlet and in the
Copper River Basin. The fog is not as widespread as yesterday
morning, due in part to a slightly drier airmass in place thanks
to the sunshine yesterday and a larger expanse of mid- and high-
level clouds helping to limit the amount of radiational cooling
overnight.

Shower activity has also developed over the northern Susitna
Valley and will persist through the day as the mid-level flow
shifts southwesterly ahead of an advancing front. With the
exception of the northern Susitna Valley and Prince William Sound,
Southcentral can expect another relatively tranquil day with an
increase in cloud cover throughout the day and, perhaps, some
scattered afternoon showers across the Cook Inlet area.

By Wednesday, all attention turns to the next weather maker in the
form of a stout area of low pressure over the northern Bering
advancing a front eastward toward Southcentral. The combination of
low pressure to the west and a building ridge along the coast
ahead of the front will begin to drive southerly gap winds through
Turnagain Arm, Knik River Valley, and the Copper River Basin
Tuesday night through Wednesday. The strongest winds expected
late Tuesday night through early morning Wednesday.

Overcast skies and steadier rain make a return to most locations,
expect the Copper River Basin, by Wednesday morning. As the front
sweeps east across Southcentral and the Gulf, a triple-point low
will develop along it east of Kodiak Island. The low and front
reach the north Gulf coast near Cordova Wednesday night where a
brief barrier jet develops. As this new low becomes the dominant
feature, the pressure gradient will shift, allowing the strong gap
winds through Turnagain Arm and the Knik River Valley to subside.
By Thursday, the front pushes inland and both the barrier jet and
southerly gap winds through the Copper River Basin weaken as rain
looks to turn showery around Cook Inlet.

&&

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

A front extending from a Kamchatka low will quickly track across
Southwest today, spreading gusty southerly winds and a band of rain
from west to east across the region. In the wake of the frontal
passage, multiple shortwaves will track eastward along the base of
the aforementioned low/trough, aiding in continued breezy and wet
conditions for the next several days. A particularly strong and
elongated shortwave is expected to pass southeastward over the
entire region on Wednesday, producing widespread rainfall with the
heaviest amounts expected during the morning. Light rain and
breezy winds will continue through Thursday and Friday morning as
the low itself slowly drops over the northern Bering and Y-K Delta
area by Thursday morning.

&&

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

Generally unsettled conditions are expected to persist for the
next several days as a large Kamchatka low slowly drifts south
toward the Y-K Delta and northeastern Bering regions. The low's
attendant front will pass over the eastern Bering and eastern
Aleutians this morning and afternoon, spreading gusty southerly-
southwesterly winds and a band of rain across those regions. Rain
showers and strong southwesterly flow will continue in the wake of
the front as multiple shortwaves round the base of the broad trough.
Rainfall will be especially heavy on Wednesday morning for the
central and eastern Aleutians as a potent shortwave traverses a
large portion of the domain. A ridge of high pressure will start
to build in behind the low for Thursday and Friday morning,
yielding drier conditions and a brief chance of clearing skies for
the western Bering and Aleutians.

&&

.MARINE (Days 3 through 5: Thursday through Saturday)...

Gulf of Alaska: Forecast confidence remains moderate for Thursday
and then low for Friday and Saturday due to moderate to major
model discrepancies. There is a chance for gale force winds across
the Gulf on Thursday as a front moves through the area. There is a
large variation in the wind solutions from Friday afternoon
through Saturday. All solutions show a barrier jet form during
this time, though there are major differences into how strong this
jet will be. No high seas are expected.

Aleutians/Bering: Forecast confidence remains moderate at this
time. Winds for the most part are expected to remain below gale
force with the exception of some small areas of gales on Thursday.
No high seas are expected.

&&

.LONG TERM FORECAST (Days 4 through 7: Friday through Monday)...

The forecast period commences with negative height anomalies at
500 mb across the mainland, the eastern Bering and the Gulf Of
Alaska. The negative height anomalies are still very prominent on
Monday over the Gulf Of Alaska. A wet forecast period is on tap
for Southcentral, portions of SW AK and the Gulf Of Alaska. On
Thursday, a closed low at 500 mb will be near Nunivak. This system
has a wide precipitation shield associated with it and will bring
another round of rain to the Mainland and the AKPEN. By Friday
night, the closed low will be south of the Alaska Peninsula and
still pumping moisture towards Southcentral and Southwest AK. The
the ECMWF have precipitation for Southcentral through Monday.
There are differences between the GFS and the ECMWF on Days 6 and
7. Most notably, the GFS is drier for Anchorage and the Mat- Su
valley Sunday and Monday. This divergence in model solutions is
being monitored.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

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