Heavy Freezing Spray Warning 217, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
558 AM AKST Thu Dec 9 2021

.ANALYSIS AND UPPER LEVELS...

A broad longwave trough is centered over the Bering Sea, with two
main embedded shortwaves affecting the region. The weaker of the
two shortwaves is located over the northern Bering, exiting
Kamchatka, and is diving southward, while the stronger and more
consequential of the two is working to strengthen a surface low
centered east of the Pribilofs which has produced blizzard
conditions there. The low is also producing widespread strong
gusty winds, heavy snow, blowing snow, and rain from the central
Aleutians all the way to the Southwest and Kodiak this morning.
Ahead of the longwave trough, Southcentral sits under a shortwave
ridge on the leading edge of the strong low. With light low-
level southerly flow in place and minimal cold/dry advection,
clear skies have turned to widespread low stratus all around the
Cook Inlet region, keeping temperatures in the teens across most
of the area. Further east, the frontal boundary that moved inland
over Southwest last night is now beginning to exit the forecast
area to the east, but continues to produce scattered, light snow
showers across the Copper River Basin.

&&

.MODEL DISCUSSION...

There is good agreement regarding the track of the low in the
eastern Bering through Friday morning as it moves into the western
Gulf. By Friday afternoon, however, there is increasing
uncertainty on the exact track of the low before it begins a
southward drive. Most of the models place the low near the
southern tip of Montague Island, whereas the GFS remains further
south over the northern Gulf. Regardless of the exact placement of
the low, there is good model agreement that cold air advection in
the wake of the low will help to produce strong northwesterly
storm-force gap winds along the Alaska Peninsula through to the
Kamishak Gap beginning Friday night.

&&

.AVIATION...

PANC...A deck of stratus keeping ceilings MVFR is expected to be
scoured out with the onset of southeasterly winds this morning
ahead of an approaching front, returning ceilings to VFR.
However, surface winds are expected to remain northerly, leading
to wind shear that persists throughout the day. As the front
passes overhead this afternoon and evening, an isolated stray snow
shower with limited impact to cigs/vsby may be possible. Friday
morning, southeasterlies aloft shift to northeasterly and relax,
reducing wind shear.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2: Today
through Friday Night)...

The next big storm is racing across the Bering and its effects are
beginning to be felt already across Southcentral this morning.
Light snow has begun in Kodiak City as of 4am, and the radar is
showing virga already overspreading the southern half of the Kenai
Peninsula. Speaking of which, the Kenai Peninsula houses both of
Southcentral's winter weather products. A Winter Storm Warning
remains in effect for the eastern half of the peninsula, with a
Winter Weather Advisory in effect for the western half,
specifically south of Clam Gulch. For the warning area, a broad
10 to 25 inches of snow are expected. Amounts closer to 10 inches
are expected from Moose Pass south to Seward, and the higher
amounts closer to 25 inches are expected from Turnagain Pass
through Portage and Whittier. Strong easterly winds are expected
with the leading front from late this morning through this
evening. This will result in significant reductions in visibility,
especially along the Seward Highway from Turnagain Pass through
Portage Valley and the eastern Turnagain Arm. In the windier
areas elsewhere along the Seward Highway, expect localized
reductions in visibility.

The leading front will exit to the northeast by midnight tonight,
if not sooner. However, the main low will then move to just south
of Montague Island late Thursday night, stall out, then drift
southward into the Gulf during the day Friday. On this track,
steady light to moderate snow will persist for much of the day
Friday, gradually ending from northwest to southeast. Winds will
remain gusty during this time, but will be significantly weaker
than when the leading front moves through today.

Now turning to the Winter Weather Advisory for the western Kenai
Peninsula south of Clam Gulch, snow will begin in this area over
the next few hours and will reach its peak intensity during the
day today. The center of the low will track just south of the
area, but with temperatures starting the day around freezing,
lower elevation coastal areas will get near or a few degrees above
freezing today, resulting in much lower snow totals in Homer.
However, at higher elevations of the Homer Bluff, the hills
upsloping the moisture will help to wring out the 6 to 10 inches
of snow forecast for the area. Snow will persist through the
overnight and into Friday, though will gradually diminish in
intensity, especially during the day Friday.

Elsewhere across Southcentral, the rest of the Prince William
Sound zones will get anywhere from 8 to 16 inches of snow from
this storm, but the winds will be weak enough where the
populations are that the impacts won't be much more than any
other typical snowfall event. Anchorage and points north will get
very little if any precipitation from this storm as its both
strong and relatively compact nature will confine much of the
snowfall to the aforementioned areas. Certainly stray snow showers
can't be ruled out but no impactful weather is expected.

Finally, once the storm moves off, the focus will quickly turn to
strong gap winds and some of the coldest, if not the coldest air
mass of the season moves into Southcentral this weekend. There is
potential for several impacts from this. First and foremost will
be extremely heavy freezing spray over many, if not all of the
coastal marine areas that border Southcentral. Mariners should use
extreme caution. A prolonged period of gusty winds is expected
from Seward to Whittier to Valdez, but much of Kodiak Island will
also be subject to these winds. While warning level gusts are not
currently expected, 48 hours of gusts of 40 to 60 mph in these
areas are likely. The gusty winds following the snow through
Thompson Pass may cause localized ground blizzard conditions this
weekend. Finally, the very cold air moving through the passes
through the Alaska Range are nearly certain to drop wind chills in
those areas to colder than 40 below and may even approach 60
below.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 2: Today
through Saturday morning)...

A powerful low pressure system currently moving south of the
Pribilof Islands this morning continues to deepen as it moves
towards Bristol Bay today. Snow and blowing snow with occasional
blizzard conditions will begin later this morning and through the
day across Bristol Bay and parts of the Kuskokwim Delta with
Blizzard Warnings for these locations. Expect heavy snow at times,
especially this morning through this evening. Snow is also
expected across the Lower Kuskokwim Valley later this morning
into the afternoon with a Winter Weather Advisory in effect for
this area. Overall most of the area will see 4 to 12 inches of
snow, however some areas just west of the western Alaska Range
will see downsloping effects with much lower snow amounts expected
there. From Hooper Bay to Toksook Bay no snow is expected as most
of it will remain to the east. Tonight into Friday morning,
expect most of the snow to wind down, with some lingering areas of
light snow across Bristol Bay and the Lower Kuskokwim Delta
through Friday. Otherwise, much colder air will usher in behind
this low pressure system especially by Saturday as lows will be 10
to 20 below zero and possibly colder in some locations.

Coastal flooding is possible for the Alaska Peninsula. Storm to
hurricane force northwesterly winds will provide favorable
conditions for the potential for coastal flooding along the north
shore of the Alaska Peninsula between Naknek and Nelson Lagoon.
Moreover, these strong northwesterly winds will coincide with the
time of high tide. Storm surge model guidance suggests storm surge
of 3 to 6 ft above Highest Astronomical Tide (HAT) for several
locations between Naknek and Nelson Lagoon. Another factor to the
flood potential is the lack of sea ice since it is early in the
season. Current sea ice remains very thin and very prone to be
broken up which will increase the likelihood of flooding along the
shores. Hence, Coastal Flood Warnings have been issued for the
Alaska Peninsula for areas between Naknek and Nelson Lagoon.

&&

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

A hurricane force low is currently developing just south of the
Pribilof Islands and will produce storm to hurricane force winds
today across the eastern Bering and Bristol Bay. This low will
also interact with colder air to produce high winds across the
eastern Aleutians and the AKPen today, with blizzard conditions
for the Pribilof Islands through 9 am. St Paul Island has already
reported blizzard conditions with visibilities of a quarter mile
or less, with periods of heavy snow and winds gusting up to 60
mph. As the low moves inland this afternoon and then into the
Gulf, storm force winds will continue south of the AKPen through
the weekend as cold air advection strengthens late Friday into
Saturday, with hurricane force gusts through the gaps and passes
likely. A second, compact storm force low will move across the
western Bering and towards the Aleutians through tonight and then
into the North Pacific Friday. As the cold air spills across the
eastern Bering and south of the AKPen, expect heavy freezing
spray to develop Friday and Saturday which could become a serious
hazard to marine interests across the area. Stay tuned to this
developing situation.

&&

.MARINE (Days 3 through 5: Saturday thru Monday)...

Aleutians/Bering... A well developed low moves into the Western
Bering with its front stretching across the Alaska Peninsula
through Monday. Confidence is good for widespread gales along the
front through Monday, with storm force winds developing Sunday
through Monday over the Bering. Seas to 19 feet on the Bering side
of the Alaska Peninsula, subsiding Saturday. Seas building to 35
feet over the Bering, and to 20 feet on the Pacific side of the
Aleutians Sunday and Monday.

Gulf of Alaska... A well developed Central Gulf low exits the
Gulf for late Saturday. Widespread high-end gales spread over the
Gulf with storm force outflow winds along the Pacific side of the
Alaska Peninsula, Shelikof Strait and Barren Islands into the
Gulf, diminishing Monday. Seas to 25 feet over the Gulf, subsiding
Monday. A new front approaches the Western Gulf for Monday.

&&

.LONG TERM FORECAST (Days 4 through 7...Sunday through Wednesday)...

Looking ahead into the extended forecast, the latest operational
model runs are in decent agreement with the synoptic scale
features, but begin to diverge in the middle of next week. An
amplified pattern remains over the Bering as a ridge of high
pressure begins to slide east in response to a deepening shortwave
trough enters the western Aleutians on Saturday. A well-
developed surface low and associated front will bring widespread
precipitation, strong winds, and elevated seas through Tuesday.
The frontal boundary is expected to track over the eastern Gulf
with the threat of winds and elevated waves along with coastal
rain and mountain snow for much of the southern-southwestern
mainland. Another low will move across the Bering and Aleutians
for the middle of next week with a continuation of winds and
precipitation. Models deviate, however, on the exact track and
position of this system but are nonetheless keying on an active
weather pattern to persist. Over the Gulf, benign conditions will
prevail as a low exits out of the area with a surge of Arctic air
spilling across the Alaska mainland. Much below normal
temperatures can be expected across the southern half of the state
from Saturday through Monday. The packing of cold air over the
coastal mountains and tightening pressure gradient will likely
keep localized winds funneling through the gaps and passes.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning 155 161
         Winter Storm Warning 125
         Coastal Flood Warning 161 181
         High Wind Warning 181 185
         Winter Weather Advisory 121 152

MARINE...Hurricane Force Wind Warning 150 155 165 170 414
         Storm Warning 119 130 132 160 171-175
                       179 180 352 412 413
         Gale Warning 120 125 128 131 136-140 176-179
                      181 185 351 411
         Heavy Freezing Spray Warning 139 140 160 180 181 185 414

&&

SYNOPSIS AND MODEL DISCUSSION...CQ
SOUTHCENTRAL ALASKA...JW
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...RC
MARINE/LONG TERM...MK/MF

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1102 AM AKST THU DEC 9 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0504 AM     NON-TSTM WND GST AKUTAN                  54.13N 165.79W
12/09/2021  E83 MPH          PKZ170             AK   AWOS

0207 AM     NON-TSTM WND GST 35 WSW AKUTAN           53.88N 166.53W
12/09/2021  E100 MPH         PKZ171             AK   PUBLIC

0202 AM     NON-TSTM WND GST 2 WNW NIKOLSKI          52.97N 168.86W
12/09/2021  E105 MPH         ALEUTIANS WEST     AK   OTHER FEDERAL

0707 AM     NON-TSTM WND GST 1 SSE COLD BAY          55.21N 162.73W
12/09/2021  E78 MPH          ALEUTIANS EAST     AK   PUBLIC

1008 AM     NON-TSTM WND GST 6 N NELSON LAGOON       56.01N 161.16W
12/09/2021  E77 MPH          ALEUTIANS EAST     AK   AWOS

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1144 AM AKST THU DEC 9 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0707 AM     NON-TSTM WND GST 1 SSE COLD BAY          55.21N 162.73W
12/09/2021  E78 MPH          ALEUTIANS EAST     AK   ASOS

            CORRECTS PREVIOUS NON-TSTM WND GST REPORT
            FROM 1 SSE COLD BAY.

&&