Heavy Snow and Winter Weather in Alaska, November 10 to 11, 2021

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
542 AM AKST Wed Nov 10 2021

.ANALYSIS AND UPPER LEVELS...
An upper trough remains largely stationary over Alaska this
morning. A smaller wave of low pressure exiting the base of the
trough is lifting northward across Prince William Sound. Isolated
to scattered snow showers are noted on radar making their way
northward as a result with Cordova experiencing the brunt of
activity. Northerly outflow winds along the coast have diminished
substantially for locations such as Seward, Valdez and Thompson
Pass, where dense, colder air to the north is being offset and
overtaken by increasing southerly warm air advection from the
Gulf. A second wave of low pressure, and one that will bring
winter impacts to Southcentral later tonight into Thursday, is
making its way across Kodiak with a baroclinic leaf feature
trailing back over the Alaska Peninsula. To the west of
Southcentral and just entering the base of the trough over Alaska
is a more subtle wave of low pressure that is moving to the
southeast and toward Bristol Bay. Light snow has been observed at
times from Dillingham to King Salmon with negligible
accumulations.

Across the Bering a shortwave trough previously north of the
Aleutians is exiting the island chain to the south. Height rises
are noted over the western Bering with the slow eastward approach
of a ridge of high pressure, and previously gusty winds across the
Aleutian Chain are beginning to taper off. One last feature noted
is the continued presence of a front draped across the Alaska
Peninsula. This front has been responsible for increased cloud
cover and periods of light snow, but is beginning to meander south
and into the North Pacific.

&&

.MODEL DISCUSSION...
Models have been in good agreement with the overall pattern
across Southcentral. A broad upper low is sitting over the state
of Alaska. Models take a trough offshore of the Gulf Coast inland
and across Southcentral through the next 24 hours. Some recent
changes that have been noted is the slower passage of the trough
through Southcentral, which will play a big factor in overall snow
amounts. Previous solutions had the trough wrap around the upper
low more quickly with increased downsloping limiting any
significant accumulation for the Anchorage Bowl. Should such a
solution verify the heaviest snow totals would likely be confined
to the Kenai Peninsula where Seward could see upwards of a foot of
snow through Thursday. However, hi-res models have began a shift
toward the trough making slower northward progress, resulting in
less downsloping for the Anchorage Bowl. This could allow for
greater snowfall accumulations through Thursday morning. The NAM
and HRRR have been consistent with each other this morning with
the GFS starting to trend slower as well.

&&

.AVIATION...
PANC...VFR conditions are expected to prevail through most of the
day on Wednesday. A trough off of the Gulf Coast will move inland
later this evening and tonight with increasing precipitation.
Some recent hi-res model guidance has slowed the passage of the
trough to the point where less downsloping is forecast and higher
snow totals may be possible for PANC. Regardless of amounts,
lowering ceilings and a reduction in visibility should eventually
promote IFR conditions through Thursday morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

A short wave is moving over the Prince William Sound area early
this morning and bringing some snow showers as it moves
northward. Even after this wave, there will be some snow showers
through the day as southerly flow aloft will keep conditions
favorable.

The main forecast challenge remains the snow amounts this evening
through Thursday across the Kenai Peninsula and Anchorage and
Mat-Su regions. This snow will be in response to the interaction
of a 500 mb low that is over the western Interior of the state and
a plume of moisture associated with a weak surface low and
baroclinic zone that will stream into the region overnight
tonight. The upper level low will elongate southward tonight and
edge eastward as the baroclinic zone brings in moisture and
lifting. The 850 mb isotherms align very nicely from north-to-
south over Cook Inlet and Kenai/Anchorage areas tonight.

What looks likely is that Seward will get a good amount of snow
tonight and either Anchorage or Kenai will as well. Which one is
the big forecast challenge. The weak surface low will elongate int
a trough over the eastern Kenai Peninsula this evening and then
rotate westward before stalling out overnight. How far west this
stalls out is the key. If the trough stalls out over Anchorage or
just west of it, there will be more than the 2 to 3 inches in the
forecast and Kenai will get less snow than what is in the current
forecast. Should this wave progress farther west, Kenai will get
more snow with Anchorage in a downslope hole and having the snow
shut off after an inch or two. This is the conundrum. Thinking has
been that the snow will favor a more westerly track due to that
is what usually happens. However, the very latest 12Z model runs
are keeping the trend started by the 06Z models to put the packed
isotherms over Anchorage which would put more snowfall there. We
will know more by this time tomorrow!

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...

Light snow is developing along the coastal area of Bristol Bay
this morning in response to an upper level wave moving across the
interior Southwest. Precipitation will taper off as the wave exits
the area by this afternoon with little to no accumulation
expected. Meanwhile, an area of low pressure developing south of
Cold Bay will trek west of Kodiak Island Island by tonight. The
bulk of moisture and snow will be confined over the AKPEN and
western Alaska Range. Light snow is possible across parts of
Bristol Bay and the Lower Kuskokwim Valley on Thursday and Friday.
Otherwise, a general troughing pattern extending from the Alaska
mainland to the eastern Bering Sea will remain anchored over the
next couple of days and eject weak shortwaves with minimal impact
expected. A persistent northerly flow pattern will help maintain
an Arctic airmass across the coastal areas and interior valleys.
Expect mostly sunny to partly cloudy skies to prevail with daytime
highs in the teens to the mid 20s and overnight lows in the
single digits to below zero.

&&

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

A weakening low pressure system moving in the southern Bering Sea
will help maintain small craft advisory level winds and showers
along the western and central Aleutians through tonight.
Thereafter, gusty, northerly winds will funnel through the gaps
and passes along the central and eastern Aleutians, Pribilofs, and
AKPEN through Friday in response to a shortwave moving on the
eastern side of a ridge. Additionally, a cool and showery pattern
will likely persist in these areas before tapering off by Friday
as the ridge axis continues to build across the central Bering.

&&

.MARINE (Days 3 through 5: Friday through Sunday)...

Aleutians/Bering...High pressure with moderate winds over the
Bering exits across the Alaska Peninsula for late Saturday.
Forecasts good through Sunday. A low moves along the Kamchatka
coast while its front pushes over the Western Aleutians and Bering
through Sunday. Increasing Southerly winds over the Western
Aleutians become gales that spread to the Central Aleutians by
Sunday. Seas building to 16 feet along the Pacific side of the
Aleutians for Sunday.

Gulf of Alaska...A well-developed Central Gulf low weakens as it
moves into the Western Gulf by Sunday. A trough extends into
Southcentral Alaska and rotates over Kodiak Island. Potential
gales around Kodiak Island are uncertain, and depend on the
trough's strength, duration and location through Saturday. Gusty
winds over the lower Cook Inlet, upper Shelikof Strait and
Kamishak Bay will continue. Seas to 16 feet across the Western
Gulf, subsiding.

&&

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

To begin the extended forecast period on Saturday, expect a
high amplitude pattern in place, with a trough and mature low
somewhere in the Gulf of Alaska, a ridge over the central to
eastern Bering Sea and a trough and potentially deep surface low
over the far western Bering Sea. The flow looks progressive, so
expect the ridge to to quickly head for mainland Alaska over the
weekend, followed behind by the trough and whatever surface
systems exist. Model spread in depiction of individual storm
systems across the Bering Sea/Aleutians is large. However, the
pattern is favorable for deep lows. Thus, for sensible weather
expect mostly dry conditions over southern Alaska for the weekend,
possibly with gap winds along the Gulf coast in the wake of the
departing Gulf low. Out west, expect storminess progressing
eastward across the Bering Sea during the weekend and likely into
Southwest Alaska by early next week. It's hard to say if these
storms will survive and make it to Southcentral.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MF
MARINE/LONG TERM...KZ/SEB

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
1218 PM AKST Wed Nov 10 2021

AKZ101-110000-
Anchorage-
Including the cities of Anchorage, Eagle River, Indian,
and Eklutna
1218 PM AKST Wed Nov 10 2021

...WIDESPREAD SNOW EXPECTED FROM WEDNESDAY EVENING THROUGH
THURSDAY MORNING...

3 to 5 inches of snow are likely across Anchorage, Eagle River,
and the Hillside from Wednesday evening through Thursday morning.
The snow is expected to be a powdery consistency, which will allow
it to be easily lofted by vehicular traffic. Thus, localized
reductions in visibility both on the highways and where snowfall
rates are heavier are likely. There remains some uncertainty as to
how much downslope drying might reduce snowfall totals. Total
snowfall amounts also could be higher than currently forecast due
to the trough stalling over Anchorage.

Drivers should slow down and use caution when driving on area
roads Wednesday night and Thursday morning due to expected
slick conditions. Leave extra space between vehicles and plan for
extra time to get where you are going. For the latest road
conditions please go to 511.alaska.gov.

AKZ125-110000-
Western Prince William Sound-
Including the cities of Whittier, Seward, Girdwood,
and Moose Pass
1218 PM AKST Wed Nov 10 2021

...UP TO A FOOT OF SNOW ALONG THE SEWARD HIGHWAY WEDNESDAY
EVENING THROUGH THURSDAY MORNING...

A storm system moving in from the Gulf will cause locally heavy
snow along the Seward Highway Wednesday evening through Thursday
morning. The heaviest snow is expected in the Seward area, where
as much as a foot of snow is currently forecast. Whittier and
Portage are expected to pick up 4 to 8 inches of snow, with up to
6 inches around Girdwood. Occasionally heavy snow will cause
hazardous conditions along the Seward Highway due to significant
reductions in visibility. There is some uncertainty as to whether
all of the storm's precipitation in Seward will be snow, or if it
will mix with rain at times. A mix with rain will reduce snowfall
totals significantly from the amounts currently forecast though it
does look to remain all snow at this time.

Drivers should slow down and use caution when driving on area
roads Wednesday night and Thursday morning due to expected
slick conditions. Leave extra space between vehicles and plan for
extra time to get where you are going. For the latest road
conditions please go to 511.alaska.gov.

AKZ121-110000-
Western Kenai Peninsula-
Including the cities of Kenai, Soldotna, Homer,
and Cooper Landing
1218 PM AKST Wed Nov 10 2021

...THREE TO SIX INCHES OF SNOW LIKELY ACROSS THE WESTERN KENAI
PENINSULA WEDNESDAY AFTERNOON THROUGH THURSDAY EVENING...

Light snow is expected to develop late Wednesday afternoon from
south to north across the Western Kenai Peninsula. The snow will
increase in intensity, becoming locally heavy at times Wednesday
night into Thursday morning. The snow will diminish late Thursday
morning through the evening, but light snow may persist across the
southern Kenai Peninsula into Thursday night. 3 to 6 inches of
snow are likely by the time the snow ends. Localized reductions in
visibility are likely along area highways from vehicular traffic,
and in areas where snowfall rates are heavier.

Drivers should slow down and use caution when driving on area
roads Wednesday night and Thursday morning due to expected
slick conditions. Leave extra space between vehicles and plan for
extra time to get where you are going. For the latest road
conditions please go to 511.alaska.gov.

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
301 PM AKST Wed Nov 10 2021

AKZ121-111215-
Western Kenai Peninsula-
Including the cities of Kenai, Soldotna, Homer,
and Cooper Landing
301 PM AKST Wed Nov 10 2021

...WIDESPREAD LIGHT SNOWFALL TONIGHT THROUGH THURSDAY MORNING...

Snow is expected to begin over the western Kenai Peninsula this
evening and will persist through Thursday morning. The heaviest
snow has shifted eastward since yesterday's model runs. As such
totals of 3 to 5 inches are expected along the Sterling Highway
between Sterling and the Seward Highway split. Lesser amounts will
occur near Cook Inlet. Although winds are expected to be
generally light, the fluffy nature of the snow may lead to periods
of reduced visibility, particularly in the wake of vehicles.