Storm Warning 107, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
456 PM AKDT Wed Oct 26 2022

.ANALYSIS AND UPPER LEVELS...

The pattern is dominated by a large upper-level trough situated
over the state, anchored by an upper-level low over the northern
Gulf. Multiple shortwaves are rotating around the upper-level low
today, keeping conditions generally unsettled across the Southern
Mainland. The first of these waves is over the northeastern Gulf
and moving east in conjunction with a compact surface low
northeast of Middleton Island. While precipitation lingers from
Prince William Sound east, the bigger story this afternoon is the
increase in northerly gap winds in the wake of the low. Winds are
gusting over 30 mph in Seward and over 40 mph in Whittier this
afternoon. The gusty winds are due to the tight pressure gradient
between the 962 mb Gulf low and higher pressures from the cold,
dense air advecting in from the interior of the state.

A second vigorous shortwave trough is dropping south across the
AKPen. This feature is associated with a surface low moving south
of King Salmon. The low was more pronounced this morning, but has
become somewhat diffuse as it hits the mountainous terrain.
Widespread snow showers persist from Bethel south to the AKPen,
where the precipitation transitions to a rain/snow mix for Cold
Bay and Sand Point. Again, the bigger story is the gusty northerly
winds. Winds gusted to 77 mph at Cape Newenham this morning with
peak gusts of 60 to 70 mph reported along the AKPen and as far
west as Akun.

Back east, snow showers continue along Cook Inlet and across
higher elevations of the Talkeetna and Kenai Mountains in response
to a weaker wave dropping south through the Susitna Valley. This
feature will help enhance gusty winds alter this afternoon. Snow
totals from the recent event across the Cook Inlet region ranged
from 1 to 4 inches across the Anchorage Bowl, 1 to 4 inches for
portions of the Susitna Valley, and upwards of 6 to 12 inches of
snow around Kenai and Soldotna.

&&

.MODEL DISCUSSION...

Latest models runs are in good agreement with the evolution of the
pattern through 12z Fri, mainly keying in on the continued cold
air advection and resultant gusty northerly gap winds and show
shower activity across the eastern Bering and AKPen. After 12z
Friday, model guidance all indicate the development of another
deep area of low pressure west of Shemya, moving east across the
southern Bering and into the western Gulf for Saturday. The main
issue is the timing of the eastward progression of this system.
The EC and GEM continue to outpace the GFS and NAM, about 12 hours
faster in the progression of the system. There is also about a 10
mb difference in the pressure of the surface low, with the NAM
and EC in the 965 mb range and the GFS and GEM around 955 mb.
Overall, guidance all shows a similar track with the low crossing
the AKPen around Cold Bay, eventually moving into the western
Gulf and keeping its associated warm front just offshore of the
Southcentral coast. Overall, there is increased confidence in the
expected impacts of this system, but less confidence in the
timing of any wind and precipitation events.

&&

.AVIATION...

PANC...VFR conditions are expected along with northerly winds.
Winds and gusts are expected to increase by late afternoon and
continue through early Friday morning. The development of a FEW or
SCT deck of low stratus a few hundred feet AGL is possible over
Knik Arm overnight as colder air moves over warmer water. However,
given the continued northerly winds, any development of fog is
not expected.

&&.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Friday night)...

The upper level jet and short-wave which brought widespread snow
to Southcentral yesterday/last night has exited eastward to
Southeast Alaska. The upper level low which has been sitting over
Southwest Alaska will move over top of a surface low spinning near
Middleton Island  this morning, then slowly exit eastward this
afternoon through tonight. Areas of snow will linger through this
evening near the northern Gulf low center and into the Copper
River Basin as short-waves rotate up and around this center.

Meanwhile, snow will taper off across the rest of Southcentral
this morning as cold (and dry) air advection kicks in. The
combination of cold air advection and tight pressure gradients
will lead to a long period of strong gusty winds across the
Gulf of Alaska coastal waters and through bays/passes along
area mountains. The strongest winds are on track for the western
Gulf and Kodiak Island tonight, along the axis of strongest cold
air advection and area of best upper level forcing on the poleward
side of an upper jet streak and front side of a Bering Sea ridge.
Temperatures will steadily fall across the region through the end
of the week. A new storm will arrive from the Aleutians Friday
night. At this point in time there is quite a bit of uncertainty
in the details. However, with arctic air in place across mainland
Alaska and generally fast zonal flow aloft, expect this storm to
take a southerly track, likely only impacting Kodiak and the Gulf
coast as we head into the weekend.

&&

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

A longwave trough dips over Mainland Alaska, with a vertically
stacked low resting in its base over the Gulf of Alaska. A tight
pressure gradient between this low in the Gulf and high pressure
in the North Pacific is contributing to strong northwesterly winds
across the Alaska Peninsula and along the Southwest coast.
Although the High Wind Warning for the Alaska Peninsula has since
expired, gusty northwesterly winds should continue for that area
through Thursday. In addition to winds, we'll see minimum
temperatures dip into the teens and single digits as northerly
flow ushers in cold air. These colder temperatures will keep
precipitation as snow as a shortwave brings showers over the
Kuskokwim Delta Thursday morning. Cold air moving over warmer
ocean waters will also lead to rain and snow showers moving from
the Bering Sea and into the Alaska Peninsula through Thursday
evening.

As we head into Friday, attention shifts to a strong surface low
that moves across the Southern Bering Sea. Models are coming into
better agreement with this storm force low, though differences
remain with its track and speed. Overall, the low looks to remain
far enough south (at least for now) that the worst of the
impacts should remain outside of Southwest Alaska. While Bristol
Bay and the Alaska Peninsula will likely see gusty winds and
light snow on Friday and Saturday, conditions look to be less
windy and drier for the Kuskokwim Delta and Lower Kuskokwim
Valley.

&&

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

Gusty northerly winds will continue for much of the Bering Sea
through Thursday, with the strongest winds at gale force for the
Eastern Bering Sea. The influx of colder air with this northerly
flow will lead to unstable conditions that produce snow or rain
showers.

Attention shifts on Thursday to a surface low moving east across
the Bering Sea. Forecast confidence is increasing that this will
be a storm force low, with the potential for hurricane force gusts
across the Central and Eastern Aleutian Islands. The influx of
warmer air with this low will lead to temperatures in the high 40s
along the Aleutian Islands and Southern Bering Sea, setting the
stage for light to moderate rain as the front moves across the
Chain from Thursday through Friday. As the low dips south across
the Alaska Peninsula late Friday night into early Saturday morning,
we could see freezing spray along the Southwest Alaska coast due
to cold, offshore flow.

&&

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

Looking ahead at the long range forecast, ensembles and
deterministic models continue to key in on broad troughing over
the Gulf of Alaska and a building ridge into the western Bering
Saturday into Sunday. A potential ~965mb low is forecast to move
from the AKPEN into the Gulf of Alaska during the 48 hour period
over the weekend while one or two embedded shortwave troughs track
southeastward into the AKPEN within a building ridge over the
Bering. As such, above average confidence exists in unsettled
conditions impacting the region from Bristol Bay into the Gulf of
Alaska up into the Gulf coast.

Across Bristol Bay, remnant northwesterly gales may be ongoing on
Saturday with timing of winds diminishing somewhat up in the air.
The GFS suggests gales may persist into the morning hours on
Sunday. Looking east and over to the Pacific side of the AKPEN,
the potential will exist for easterly gales over the northern Gulf
on Saturday as a front encroaches upon the Gulf coast resulting
in a potential barrier jet. While the windiest conditions will
likely remain offshore, the front may bring northeasterly gales
directly across Kodiak Island before the low pushes further east
later in the day. Models are in relatively good agreement with
depicting westerly storm force winds across the southern extent of
the Gulf both on Saturday and Sunday. Cold air advection being
reinforced over the eastern Bering will support gale to storm
force gap winds through the AKPEN and Kamishak Bay into Sunday.
These enhanced westerly winds should gradually weaken to gale
speeds on Monday as the pressure gradient slowly relaxes. While
snow will be possible for coastal areas from Kodiak to Prince
William Sound, strong southeasterly flow at the surface and ahead
of the low will likely keep temperatures above freezing and
precipitation as mostly rain.

Confidence begins to decrease more substantially in the forecast
beyond the weekend. Ensembles suggest high pressure over the
Bering will be overtaken by the next North Pacific low late Monday
into early Tuesday. Depending on the strength and placement of
the low, southeasterly storm force winds may become widespread
over the eastern Bering by Tuesday. However, aside from the
stronger solution of the GFS, both the Canadian and ECMWF remain
much weaker and further west, which was also true of the previous
long term discussion.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM 130 131 132 150 155 352 GALE 121 136 137 138 160
165 170 171 172 174 175 176 177 178 179 180 181 185 351 412 413
414. FIRE WEATHER...NONE.

&&

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