Small Craft Advisory 849, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
527 PM AKDT Tue Oct 25 2022

.ANALYSIS AND UPPER LEVELS...

Westerly flow along with a strong upper level jet is moving
across the southern Bering Sea and the Aleutians. A short wave
trough over the northwestern Bering is trailing downstream of a
large trough over the eastern Bering. Clouds ahead of this front
are beginning to filter into the Copper River Basin from the west
as a low moves into the Kuskokwim Delta this afternoon. Radar
returns show precipitation falling across Southwest Alaska and
beginning to fill in through Southcentral, west of the Chugach and
Kenai Mountains and the Susitna Valley as of noon. Lower
visibility is reported on surface observations along the Southwest
coast. Seldovia reported rain while nearby Homer is reporting
mixed rain and snow. Kenai and Soldotna just reported shortly
before noon, light snow.

&&

.MODEL DISCUSSION...

The general pattern is on track for the near term with slight
differences with the surface low moving along the northern Gulf.
This would lead to implications with the details regarding timing,
duration, and intensity of snowfall west of the Kenai and Chugach
mountains. The next challenge with the models is with a low
entering the western Bering towards the end of the week.

&&

.AVIATION...

PANC...LLWS due to higher, southeasterly winds aloft crossing the
Kenai and Chugach Mountains is possible this afternoon. Wind
shear is expected to gradually lift later in the evening.

&&

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

Models continue to struggle with the location of the triple point
low across the northern Gulf late this evening through tonight.
This complication will affect the strength of the downsloping
component across the mountains, the extent of warm air advection
into Prince William Sound, and the location of the barrier jet
ahead of the low. The faster progression of the storm will limit
heavy accumulation in any given location. Snow will begin to taper
off across the region Wednesday as cold/dry air advects into the
domain behind the storm. This will give way to widespread gusty
winds Wednesday afternoon through Thursday night and will aid in
limiting the drop in temperatures initially. With the cold air
continuing to advect in, expect colder temperatures through the
end of the week. A Winter Weather Advisory for blowing snow has
been issued for Thompson Pass starting 4 AM AKDT Wednesday. With
models still struggling with the track of the aforementioned
triple point low, uncertainty lies in how much snow the Pass will
receive and the timing of the precipitation. The Canadian Regional
is showing the snow lingering as the low tracks across the Gulf,
meaning the strong northerly winds could increase when snow is
still falling. Other models show the brunt of the snow staying
more on the mountains and off of the road system and not linger in
the area. Regardless, colder temperatures and drier air will make
the snow light and fluffy in nature, which will allow the snow to
be more easily transported by winds. Therefore, plan for reduced
visibilities in the area and use caution while driving. For
Wednesday night into Thursday, the strongest winds will be along
the south side of the Alaska Peninsula, across the western Gulf,
and Kodiak Island Wednesday night with wind gusts up to hurricane
force for Shelikof Strait up to Kamishak Bay and the Barren
Islands corridor and to storm force for the rest of the Kodiak
Island waters. Meanwhile, cold air advection from the Alaska
Interior spreading southward across Southcentral will lead to
strong gap winds through mountains passes and coastal bays through
the end of the week.

&&

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

A mature low moved across the Bering and inland today near
Toksook Bay and Nightmute with an estimated surface pressure of
973 mb. This low still has a tight pressure gradient force
associated with it that is influencing much of the Southwest
Alaska and Bristol Bay. This system will result in widespread
gusty winds, a wintry mix, and the possibility for high surf from
Kipnuk to Togiak...and potentially other portions of Bristol Bay.
Expect a batch of unsettled weather most of this forecast period.
When the upper low moves inland expect light showers into
Thursday morning. For the entire event, accumulations will not be
significant. Also noteworthy, in the wake of the frontal passage
expect widespread cold air advection with temperatures plummeting
to the 20s along the coast by Thursday morning. But the interior
locations the temps will range from the teens to a few locations
in single digit territory Thursday morning. Friday morning will be
even colder and more interior locations will be in the single
digits.

A high surf advisory is in effect for Kipnuk down to Togiak. A
high wind warning has also been issued for the Alaska Peninsula
including Cold Bay early Wednesday morning through Wednesday
afternoon. Gusty winds through the bays and passes south of the
AKPen will remain gusty through Wednesday night.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

A mature low moved across the Bering and inland today near
Toksook Bay and Nightmute with an estimated surface pressure of
973 mb. This low still has a tight pressure gradient force
associated with it that is influencing much of the Bering. Gale to
storm force winds will continue and the threat of enhanced seas
will continue. The upper level jet that is driving this system is
directly over the Aleutian chain and it has a jet core of 175
knots. This is a fast moving system. In the wake of the frontal
passage expect widespread northerly flow and cold air advection.
Also a transient ridge will move over the Western Aleutians on
Wednesday. By Thursday morning, a new Pacific low will be on the
horizon for Attu Island. The dynamics are not impressive with this
next low but it will bring showers to the Western and Central
Aleutians late Thursday and Friday.

&&

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

Not much has changed for the long term since the previous
discussion. Colder temperatures will continue to be the main
headline for southern mainland Alaska as a longwave trough
settles over the state through at least Monday. Synoptic scale
model agreement is decent, with uncertainty increasing into Monday
as model solutions diverge.

The extended period will begin on Saturday with a surface low
dipping south across the Alaska Peninsula and moving into the Gulf
of Alaska. The GFS and ECMWF deterministic models are in good
agreement with this feature, though the Canadian model has this
low moving faster across the Gulf and remaining further south. For
now, it looks like a tight circulation around this low will keep
snow limited mostly to Bristol Bay, Kodiak Island, and the North
Gulf coast. The primary hazard for this system will likely be
winds, with winds of at least gale force (with storm force
possible) around this low. Given uncertainties in the low track,
where the strongest winds will set up remain uncertain. However,
ensembles are suggesting it is more likely than not that outflow
winds through Kamishak Gap and across the Alaska Peninsula will be
gale force from Saturday through Sunday.

As we head into Monday, model agreement worsens as they struggle
with how two upper level shortwaves (one in the Western Bering
Sea and one in the North Pacific) will phase late Sunday. Among
the different solutions, the GFS's looks like it would be the most
impactful as it shows these two features merging to produce a 963
mb Bering Sea low that moves into Western Alaska on Tuesday. The
surge of warm air northward with this solution, as well as winds
at storm force, could be hazardous for Western Alaska. The
Canadian solution shows a similar track, though it keeps the low
weaker. Finally, the ECMWF models shows the bulk of the energy
remaining along the Aleutians rather than Western Alaska. Overall,
unsettled weather is expected by Monday and Tuesday, though the
details remain uncertain at this time.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 121 131
         High Wind Warning 181
 High Surf Advisory 155 161.
MARINE...STORM 119 130 131 132 138 150 155 160 165 180 181 GALE
120 121 125 129 136 137 139 170 171 172 173 174 175 176 177 179
185.

FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...VR
SOUTHCENTRAL ALASKA...NS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PS
LONG TERM...KC