Gale Warning 561, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
529 AM AKDT Mon Oct 17 2022

.ANALYSIS AND UPPER LEVELS...

The broad upper level low near the Kuskokwim Delta coast weakens
and shift southward through tonight into Tuesday morning, merging
with a North Pacific low. High pressure over the western Bering
pushes eastward ahead of a front extending off a low centered over
eastern Russia. There is a swath of cold air advection following the
front that will move over the Bering Sea mid-week. Multiple upper
level shortwaves pass over the Gulf of Alaska and into
Southcentral Alaska ahead of the North Pacific low. There is good
consensus that this developing system will end up taking a more
easterly track, with its center aiming for the region between
Cordova and Yakutat. The brunt of the impacts will most likely
affect the Southeast portions of the State, but Southcentral could
see periods of unsettled weather as well.

&&

.MODEL DISCUSSION...

Models remain in good overall synoptic agreement through the short
term. There was some hinting yesterday that the incoming North
Pacific low would a more easterly track last night, and newer
model runs have since confirmed that. There is still some
light inconsistencies, but the general strength and track of the
system is being handled better.

&&

.AVIATION...
PANC...Mostly VFR conditions should persist. Some gusty southerly
winds will continue into the early morning hours before becoming
light. Chance for some rain showers late morning/early afternoon
may bring conditions down to MVFR at times.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3;
Today through Wednesday night)...

A surface trough and associated upper-level shortwave will lift
north from the central Gulf across Southcentral today. These
features will keep conditions unsettled throughout the day, with
widespread showers along the immediate coast and periods of
shower activity farther inland. There is some added instability,
mainly colder air aloft, with this shortwave that could trigger
some isolated thunderstorms from the northern Gulf to the coastal
mountains through early afternoon. The upper-level wave lifts into
the interior by Tuesday morning as a transient upper-level ridge
moves in. The developing easterly flow aloft will shift the bulk
of the shower activity along the eastern Kenai Peninsula and the
Alaska Range.

By Tuesday, the main focus will shift to the North Pacific where a
hurricane-force low will move north to the Southern Gulf. The
leading occluded front will sweep northwestward over the northern
and western Gulf by Tuesday afternoon with widespread rain from
the immediate coast to Kodiak Island and storm-force winds over
the open water. This front rapidly weakens as it, and the
associated upper-level wave push inland. This feature will
increase northerly gap winds and push precipitation along the
coastal mountains and across the Copper River Basin, falling as
mix of rain and snow, both at elevation and over the western
Copper River Basin. The low is then expected to continue to
rapidly weaken as it moves east toward Yakutat. A mix of rain/snow
showers will linger across the mountains as the flow aloft turns
northerly.

A secondary upper-level wave is then expected to lift northeast
from the AKPen Wednesday night into Thursday morning with light
precipitation developing from Cook Inlet north to the Susitna
Valley. Temperatures should remain warm enough at lower
elevations for rain. However, higher elevations such as the
Anchorage Hillside and northern Susitna Valley could see some
light snow. As this system lifts to the Copper River Basin, a
frontal system will move into the western Gulf with another round
of precipitation for Thursday.

&&.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 2: Today
through Wednesday)...

A broad upper low remains over the Bering Sea with another
shortwave generating scattered rain showers in Bristol Bay and
wintry mix in the Kuskokwim Valley. By tonight, the low is
expected to weaken in response to a high pressure system building
overhead with cool, dry conditions. Periods of rain showers,
however, will persist at least through Tuesday night for the
Alaska Peninsula in addition to north- northwesterly gap winds.
Otherwise, daytime temperatures will range in the 30s and 40s with
overnight lows below freezing under party to mostly cloudy skies.
After a brief break of drier weather on Tuesday, an upper trough
and surface low sets up over eastern Russia, advancing a front
eastward toward western Alaska. Along and ahead of the front,
steadier precipitation and southerly winds arrives Wednesday
afternoon/evening.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 2:
Today through Wednesday)...

A broad low pressure system extends across the eastern Aleutians
and southern Alaska Peninsula. North-northwesterly gap winds along
with scattered rain/snow showers continues across the Bering Sea
and Aleutian Chain as cold air streams over the relatively warm
sea waters on the back side of the low. Winds are expected to
diminish along with precipitation tapering off tonight as a ridge
of high pressure builds overhead. Meanwhile, a front extending
ahead of a strong low in the Sea of Okhotsk will advance a front
toward western Alaska. Along and ahead of the front, storm force to
gale force southerly winds with moderate to heavy rain moves
across the Bering Sea and Aleutian Chain between tonight and
Wednesday.

&&
.LONG TERM FORECAST (Days 4 through 7: Thursday through
Sunday)...

Unsettled weather is in store for Southern Alaska and the Bering
Sea through the extended period, with model agreement about
average. The long term begins on Thursday with an upper level
trough over much of the Bering Sea. An occluded low embedded
within this trough pushes its front into Mainland Alaska
through Thursday, bringing elevated winds and rain/snow.

The next feature to watch is a shortwave in the North Pacific
Ocean that spins up a surface low on Friday. Models have not been
in good agreement, though it appears that they may be slowly
converging on a solution. The GFS and Canadian deterministic
models show this low tracking south of the Aleutian Islands on
Friday, then moving into the Gulf by Saturday night as it runs up
against a ridge. However, the deterministic ECMWF model shows this
low remaining in the North Pacific due to weaker ridging. Beyond
the track, there are also differences in the strength of this
low. The deterministic Canadian model has been the most
aggressive, with pressure dropping as low as 970 mb with the low
center. The 12Z GFS had been a bit less aggressive (with minimum
pressure around 1000 mb), though the latest model run is
suggesting that the low center will drop to around 990 mb with a
trend towards stronger winds. Both the deterministic Canadian and
GFS models have winds of at least gale force, with a period of
storm force winds around the backside of the low. The
deterministic Canadian model is even suggesting a brief period of
hurricane force winds, though whether that plays out remains to be
seen. Uncertainty remains high, with ensemble members showing a
broad range in sea level pressure associated with this feature.

By Sunday, the aforementioned low should depart the Gulf, leading
to gusty outflow winds through Kamishak Gap. Further west, the
presence of an upper level low over Eastern Russia suggests more
unsettled weather is on the way, though the specifics remain
uncertain. The question is how strong a shortwave rounding this
upper level low will be, and how quickly its associated surface
low will occlude. These factors will affect the maximum winds
expected with this low and the potential development of a low at
the triple point.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm Warning 131 132 177 178 351 351 411-413
		 Gale Warning 119 120 130 136 137 138 150 175 176 185
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KM
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MF
LONG TERM...KC