Gale Warning 476, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
514 AM AKDT Sun Aug 28 2022

.ANALYSIS AND UPPER LEVELS...

A broad trough is nestled over much of the Alaska mainland, with
a low center moving into the western Gulf of Alaska near Kodiak
Island. While flow is weak from the surface to the upper levels
over the inland portions of the state, the opposite is true
further west where northerly flow is observed at the surface and
unidirectional aloft with a 150 kt jet. A ridge axis is over the
Western Aleutians and the aforementioned northerly flow is moving
along a tightened pressure gradient spanning from the northwestern
Bering to the Central and Eastern Aleutians.

On radar, convective showers are moving easterly along the
northern periphery of the low. Reflectivity echos are observed
along the entire Gulf coast into Southwestern Alaska towards
Bristol Bay. Several lightning strikes appeared after midnight
just east of Kodiak Island. The only real clear location across
the area is near Adak, but low stratus and fog is developing
nearby to the east and west.

&&

.MODEL DISCUSSION...

The synoptic features are slow moving and overall, models are
aligning well through roughly midweek. Once another low moves into
the northern Bering and another develops in the northern Gulf,
agreement starts to diverge. Minor challenges in the short term is
determining when and where periods of fog will develop during the
overnight hours and also for the periods of light showers and
convection associated with the trough.

&&

.AVIATION...
PANC...Generally expect VFR conditions and light winds to
continue. Areas of low clouds/fog may develop in the morning.

&&

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

An upper-level low situated south of the Alaska Peninsula this
morning will slowly drift eastward to the eastern Gulf through
Tuesday. Multiple weak waves and vorticity maxima will rotate
around the low as it moves into the Gulf. Expect periods of shower
activity across interior Southcentral through the next several
days along with occasional bouts of rain along the coast. With
the upper-level low well to the south, a developing northeasterly
flow over Southcentral will allow for some drier air to work in,
resulting in some clearing and partly sunny skies away from the
coast Sunday and Monday afternoon and evening.

Any clearing during the day will also allow high temperatures to
warm back into the 60s. The warmer surface temperatures combined
with the aforementioned waves/vorticity maxima and cooler air
aloft will all combine to destabilize the atmosphere over the
interior Sunday and Monday afternoon. The result will be a
redevelopment of showers along with the chance for isolated
thunderstorms, especially across the Susitna Valley and western
Kenai Peninsula. Along the coast, a front associated with a broad
low parked underneath the upper-level low will lift north with
rain overspreading the coast by Sunday evening. The front stalls
through Monday with rain lingering.

The other issue will be areas of fog developing during the
overnight hours for valley locations and sheltered coastal
locations. The likelihood of fog development will be dependent on
the extent of clearing and radiational cooling.

The upper-level low opens to a wave and moves over the Alaska
Panhandle for Tuesday. However, a frontal system quickly
approaches the region from the west with increasing clouds,
moisture, and southerly winds.

&&

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

An active jet stream is helping to dig a trough into the Gulf of
Alaska this morning. Mild northerly winds over Southwest will
promote drier conditions through much of the day. Further north,
an upper low over the Chukchi Sea is expected to send a shortwave
trough southward across the region later this afternoon and
evening. Thus, an increasing chance for isolated to scattered
showers will develop over the latter half of the day, primarily
over the higher elevations. The bigger news, however, is that a
break in clouds and calmer conditions should allow many areas to
warm into the low 60's.

Into the start of the work week models continue to trend drier on
Monday as high pressure builds over Southwest between systems.
The caveat is that an approaching trough into Southwest will
likely result in increased cloud cover as well as increasing
northerly winds. Afternoon highs may stay below 60 degrees in
various areas depending how quickly clouds develop or spread over
the region. Attention then turns to Tuesday where a stacked low
over the northern Bering is forecast to bring a front into
Southwest through the morning hours. Morning showers are forecast
over coastal areas, beginning first over the Kuskokwim Delta.
Precipitation will then expand eastward with the front's progress
across Southwest. Previous winds out of the north will become
southerly with the front's approach. Gusty winds will become
common through Tuesday night with wind speeds ranging from 10 to
15 mph and higher gusts.

&&

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

A strong ridge of high pressure will remain over the western
Bering for the next couple of days. Benign winds and generally
clear skies are forecast for the Western Aleutians. A strong upper
level jet, located on the backside of a developing trough over
the Gulf of Alaska, will promote enhanced northerly winds over the
eastern Bering. Within this region, an axis of small craft winds
and higher gusts will stretch from Nunivak Island southward across
the Pribilof Islands and, finally, into the Eastern Aleutians
through Sunday night. By Monday, the axis of winds will shift
eastward into Bristol Bay while the Eastern Aleutians and southern
Alaska Peninsula continue to see enhanced gap winds through
Monday evening.

High pressure then begins to break down and become shunted
southward into the North Pacific by Tuesday, as a Kamchatka low
amplifies into the northern Bering along with a front sweeping
across the Aleutians into the eastern Bering by Tuesday afternoon.
Along and behind the front a broad area of westerly small craft
winds are forecast to develop. These winds will blanket much of
the western and northern Bering through Tuesday afternoon,
eventually shifting southward and into the Aleutians by Tuesday
night.

&&

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

Gulf of Alaska: Expect winds less than 35 kts and seas less than
20 ft for the Day 3 through 5 period.

Aleutians/Bering: Expect winds less than 35 kts and seas less than
20 ft for the Day 3 through 5 period.

&&

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

Looking ahead into the longterm forecast, models advertise a
similar synoptic pattern through the middle to end of next week.
On Wednesday, an upper-level trough is located over the central
Gulf of Alaska and a longwave upper trough stretches across the
Bering Sea. The shortwave Gulf trough will quickly depart to the
east while the large Bering trough drops southeast across much of
the Mainland through Friday and then exits into the Gulf on
Saturday. The primary uncertainty in the longterm lies with
deterministic models disagreeing on various feature details. For
instance, the GFS is weaker with a system approaching the
Southwest coast on Wednesday compared to the Canadian/EC.
In addition, uncertainty increases for Friday and Saturday in
regards to the strength and placement of a developing surface low
over the Gulf. Thus, forecast confidence in winds and
precipitation timing and amounts decreases towards Days 6 and 7,
especially across Southcentral and the Gulf. Nonetheless, expect
a generally wetter pattern to continue through the longterm for
both the east and west domains.

&&

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

&&

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