Gale Warning 549, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
425 PM AKDT Tue Oct 4 2022

.ANALYSIS AND UPPER LEVELS...
The main feature aloft is a closed low pressure dropping south of
the Alaska Peninsula. A strong developing system over eastern
Russia is beginning to pump up a ridge over the Bering Sea which
is causing the upper low to cut off from the upper level jet
stream. Downstream of the AKPen trough, several disturbances are
propagating through the flow in the eastern and southern Gulf of
Alaska.

The surface low associated with the upper level trough is fairly
broad with a diffuse center, south of Kodiak Island. The system
does have some fairly defined fronts, a broad warm sector over the
Gulf of Alaska, though the front is hanging up along the coastal
mountains. The cold advection on the back side is evident in the
open cell cumulus south of the Aleutians. Most of the associated
rain is from Kodiak Island northward along the northwestern Gulf.
The Cook Inlet region remains mostly dry from cross-barrier flow,
and some areas of light rain are moving into the Bristol Bay
region.

&&

.MODEL DISCUSSION...
In the upper levels, guidance is in great synoptic agreement with
the evolution of the pattern. The upper low over the AKPen drops
well into the northern Pacific, while a stronger shortwave rotates
to the northern Gulf of Alaska. There are some slight timing and
track differences as this feature moves inland Wednesday
afternoon. Otherwise, the next feature of interest is a strong
cold front toward the weekend with good model agreement regarding
timing and strength of the feature for being so far out in time.

&&

.AVIATION...

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

&&

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

A fairly active pattern is expected for Southcentral over the next
few days as a trough of low pressure moves westward across the
Gulf combined with a coastal ridge along the eastern Gulf. The
resulting synoptic pattern will result in strong Turnagain Arm
winds from Wednesday afternoon through Friday evening. The peak of
these Turnagain winds will be Wednesday evening. These sustained
winds will be near gale force with gusts to gale force. There is
some uncertainty with respect to these winds bending into
Anchorage.

Another thing will be rain on Wednesday and Thursday. The rain
will mostly be on the south side of the Chugach Mountains as
downslope forcing is expected to be strong. Temperatures will be
quite warm Wednesday afternoon due to strong warm air advection
aloft combined with downslope. Anchorage and the Matanuska Valley
could see highs in the low to mid 60s F.

&&

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

The forecast remains on track and the low center is currently
south of the Alaska Peninsula and moving into the North Pacific
Ocean. Cloudy and wet weather will continue through this afternoon
and gradually taper off from north to south across Southwest
through tonight. Offshore flow will continue as the low exits and
a ridge builds into the Southwest tonight.

Quieter weather, with light winds and clearer skies should
prevail Wednesday until Thursday. A front extending off a low in
the Chukchi Sea will track into the Kuskokwim Delta beginning
early Thursday morning and slowly progress inland and through
Bristol Bay Thursday and Friday. A small surface low near the
Barren Islands will likely lead to gusty southeasterly to
southerly winds Thursday.

&&

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

Northerly gales through the gaps of the Alaska Peninsula and
Eastern Aleutians should diminish Wednesday morning as an
occluding low continues towards the North Pacific Ocean. A ridge
will then squeeze eastward bringing a brief break to the weather
across the Central Aleutians through the Pribilofs Wednesday
morning.

Behind this ridge, a low near the Kamchatka Peninsula will push a
front into the Western Bering Sea. Some delay of clouds and
precipitation reaching Attu than anticipated, though it is
expected to still arrive later this evening as the front interacts
with a shortwave moving north along the Western Pacific Ocean.
This will help strengthen winds and rain along the front, leading
to increased rainfall rates and southerly winds at gale force. As
the low itself tracks further north and moves into the Chukchi
Sea, winds are expected to weaken and rain amounts will
subsequently decrease along the Southern Bering Sea by Wednesday
evening. Rain and wind is expected to continue through the
Northern Bering, but how far it remains south during the trek
eastward is still somewhat uncertain, especially for the Pribilofs
Wednesday night. By Thursday, calmer conditions should prevail
across much of the region, except in the Eastern Bering Sea where
the front will linger through Friday. Friday night into Saturday,
cold air in the mid levels could filter behind the frontal
passage.

&&

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

The synoptic pattern through the long term period shows upper
level ridging over Western North America with primarily upper
level troughing over east Russia and the northwest coast of
Alaska. In between these main features will be transient upper
level ridges and troughs which vary from model to model. Some are
deeper with the trough moving across southern Alaska Sunday while
others keep a more zonal flow. A stalled front remains across
Southwest heading into Saturday keeping the region unsettled.
Another stronger upper level shortwave is expected to traverse the
northern Bering and barrel its way into Southwest Friday night
through Saturday. This will act to reinforce the front especially
across the Middle Kuskokwim Valley and Bristol Bay leading to
upslope in these areas, especially the Lake Clark National Park
and Reserve. This will lead to enhanced precipitation rates in
this area. Further east, southwesterly flow will be aimed north
through Cook Inlet Saturday and then Prince William Sound for
Saturday/Saturday night leading to heavier precipitation.

Behind this first system, much colder air will filter in behind it
especially across Southwest/northern Bering Sea where 850 mb
temperatures may fall to as low as -8 to -9 degrees Celsius. Some
of this cold air will get funneled through the Kamishak Gap
leading to increased winds through the Barren Islands area
potentially to gale force. Enough of this cold air may filter into
the northern areas of Southcentral namely Broad Pass area from
Chulitna on north towards Cantwell and across the northern Copper
River Basin (Paxson area). The main issue here though will be if
the cold air can move into the area before the precipitation ends
to bring some snowfall. There is the potential that snow may fall
on the road system in these areas. Also, this could potentially
lead to the first widespread freeze of the season for Southcentral
but will be highly dependent on if it can clear out or not. If it
stays cloudy it most likely would stay in the mid to upper 30s.

Sunday looks to be a transition day where heights may rise some
behind the departing upper level trough. However, another system
looms right on the heels of this first one leading to another
round of unsettled weather for much of southern Alaska, the
Bering Sea/Aleutian Chain Monday/Tuesday. Depending on the exact
track and intensity of this low some warmer air may be brought
northward into Southcentral raising snow levels some. Southwest
Alaska where the deeper cold air will be may have the potential to
see the first accumulating snow of the season especially across
the Kilbuck/Kuskokwim/Ahklun Mountains. Some of the villages also
might have the potential at seeing the first snowfall but too
uncertain to pinpoint which ones yet. Most likely it would be
either the Kuskokwim Delta, western Middle Kuskokwim Valley and
western Bristol Bay.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 411 412 155 172 174 178 185 119 120 131 132
138.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...ML
SOUTHCENTRAL ALASKA...ED
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...VR
LONG TERM...MV