Small Craft Advisory 32, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
539 PM AKST Wed Jan 12 2022

.ANALYSIS AND UPPER LEVELS...

A shortwave trough continues to push across the northern Gulf as
seen on satellite. With radar showing rain and snow across Prince
William Sound with another band of mixed precipitation moving
across the Kenai Peninsula. And light snow across the southern
Susitna Valley. Temperatures are in the 20s and 30s with rain near
coastal locations and snow reported inland with spotty reports of
sleet near Soldotna. Across Southwest Alaska a shortwave is
moving through the Kuskokwim Delta with radar showing snow mainly
just west of Bethel towards the coast. A few snow showers also
showing up south of King Salmon. Observations across the Kuskokwim
Delta show temperatures in the teens with snow and visibilities
of 1 to 3 miles with stronger winds along the Kuskokwim Delta
Coast up to 35 mph and near a quarter mile with snow and blowing
snow at Chevak. The remainder of the Bering and Aleutians shows a
front across the southern Bering with winds generally less than 35
knots and a few rain and snow showers.

&&

.MODEL DISCUSSION...

Models have come into better agreement with the stronger GFS
solution as a strong front and accompanying low moves into the
Gulf through Thursday, with only subtle differences. The biggest
forecast challenges will be precipitation types for Southcentral
and parts of Bristol Bay. As well as winds and QPF amounts for
Southcentral. A couple of inches of rain possible Thursday and
Friday in coastal locations like Seward and heavy snow in the
coastal mountains including Alyeska Ski Resort above 1000 feet or
so.

&&

.AVIATION...

PANC...Light snow is expected this evening with some MVFR
conditions with it. Biggest question for the TAF is whether these
MVFR ceilings will be able to dissipate after the snow ends or
not. There should be a northerly breeze developing at that time so
initial thought is that they should mostly improve. Look for low
level wind shear to develop tomorrow morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2...Wed
evening through Friday)...

A weak shortwave moving over the Kenai Peninsula and into the
Susitna Valley this evening will bring a chance for snow and a
brief period of freezing rain from Anchorage north to the southern
Susitna Valley. Any freezing rain that does fall will remain at a
light glaze with up to an inch of snow possibly shortly after.

The main weather story for the next two days will be a strong
front extending north from a storm tracking from the Southwest
Gulf Thursday into Bristol Bay on Friday. The Gulf Coast,
particularly the eastern Kenai Peninsula, will receive the brunt
of the storm with moderate rain at sea level and heavy, wet snow
above 800 to 1200 ft in elevation. Early Thursday morning the
storm should begin as snow at sea level, quickly transitioning to
rain at Seward and the Portage Valley. Strong mass convergence
and easterly winds near Whittier will allow strong winds to push
over Portage Pass and into the eastern Turnagain Arm, with gusts
to 65 mph through Portage Valley possible throughout the day
Thursday. Any remaining snow on the roadways, as well as ground
temperature near freezing, may cause ice on the roadways similar
to, but to a slightly lesser extent than was observed two days
ago. Sustained warm temperatures and winds coming through Portage
should eventually mitigate any ice problem. In Turnagain Pass,
temperatures at the surface will remain around freezing, with some
warmer air aloft, heavy wet snow is expected. 12 to 18 inches is
expected with up to 2 feet possible on the higher end. Due to the
heavy nature of the snow and rapid accumulation, a Winter Storm
Warning has been issued from Portage to the Hope Cutoff. The
highest snow accumulations and strongest winds are expected from
10 am to 5pm.

As the storm progresses, winds aloft will switch from east to
southeast to south-southeast. This will transition heavy
precipitation away from Turnagain Pass and north towards the
Girdwood area, but snow is likely to continue through Friday, but
rates will slowly drop throughout the day. For Seward, the wind
transition will also bring higher rainfall totals due to less
downsloping effect. Total rainfall is estimated to be between 1.5
and 1.75 inches, which may cause localized urban flooding/ponding
of water due to the poor draining in winter conditions.

Valdez and Thompson Pass are also likely to receive snow, with the
heavier accumulations starting around 1pm Thursday and going
through the evening before slowly tapering off on Friday. With the
transition of winds from southeast to south, a transition to a
rain snow mix is possible on Friday, through uncertainty for
precipitation type remains high. By Friday evening the low will
dissipate over the western Interior, bringing an end to the snow
over most locations.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Day 1 through 3: Tonight
through Sat)...

Snow near the Kuskokwim Delta will gradually move northward and
diminish through tonight. The next low pressure system is
beginning to push its outer bands into the Southwest. Chances for
precipitation will continue to increase tonight into Thursday and
while many areas will be snow, a wintry mix or even a change to
rain or freezing will be possible for places around Bristol Bay,
including Pilot Point to King Salmon and Iliamna Thursday morning.
Northeast winds will increase out over the Southwest Thursday
morning and blowing snow will be possible. This timeframe is a
tricky precipitation forecast as warmer air advects into the area
and the extent of how strong downsloping will try to dry out the
atmosphere near King Salmon. Cold air will usher in behind this
system and by Friday and lingering precipitation throughout the
day should turn to all snow by Friday morning.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Day 1 through 3:
Tonight through Sat)...

A large low will progress towards Southwest Alaska but its
western extent could impact the Eastern Aleutians as winds turn
northerly into Thursday morning and winds flow through gaps. A
shortwave accompanying northerly flow near St Paul Island will
keep snow over the area through Friday morning before diminishing
throughout the day. Heavy freezing spray over the northern Bering
Sea may be a problem near Saint Matthew Island over the next few
days. To the west, a North Pacific low will lift north on Friday
night, increasing chances for rain and snow from the Western
Aleutians to Central Aleutians through Saturday afternoon.

&&

.Marine (Days 3 through 5: Saturday through Monday)...

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

Bering Sea: An area of low pressure will track from the North
Pacific and enter the western Bering Sea starting on Saturday, and
then remain stationary through early next week. A swath of gale
force winds and seas above 20 ft at times are expected for south
of the Aleutians and much of the Bering Sea at least through
Monday.

&&

.Long Term Discussion (Days 4 through 7: Sunday through Wednesday)...

Looking ahead into the extended forecast, the latest operational
model runs are in decent agreement with the evolution and
progression of the synoptic scale features for early next week but
diverge in the specific details towards the end of the period.
For Southcentral, most of the precipitation will shift east toward
the Panhandle as an area of low pressure near the Kenai Peninsula
starts to weaken, leaving a brief period of dry weather from
Sunday through Tuesday. The rest of the mainland, including
coastal and interior Southwest, is expected to be relatively dry
with near to below normal temperatures. Beginning on Wednesday,
models seem to hint on a frontal boundary extending from a center
of a low, bringing precipitation and wind from Kodiak Island
northward to the Alaska Peninsula, and into the southern mainland.
Where the uncertainty emerges is the track, position, and timing
of the front that still needs to be ironed out with subsequent
model runs. Out west, a stationary low near the western Aleutians
will keep a wintry mix of rain/snow and gusty winds at times along
the southern portion of the Aleutians into the Bering Sea through
the middle of next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Storm Warning 125.
MARINE...Storm Warning 119.
Gale Warning 120 125 130 131 132 136 137 138 139 150 155 351 352.
Heavy Freezing Spray Warning 185 414.
FIRE WEATHER...NONE.

&&

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