Area Forecast Discussion
Issued by NWS Anchorage, AK

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

000
FXAK68 PAFC 270054
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
454 PM AKDT Thu Mar 26 2020

.ANALYSIS AND UPPER LEVELS...
A fairly flat upper level ridge is moving from the eastern Bering
toward mainland Alaska. A series of short-waves are tracking
southeastward down the east side of the ridge, with Arctic air
advecting southward across Southcentral Alaska and into the Gulf.
As a result, gap winds have developed through gaps of the Alaska
Range as well as through bays and passes along the north Gulf
coast and Prince William Sound (including Seward, Whittier, and
Valdez areas). Skies are mostly clear across the southern
mainland, with some patchy low clouds and fog in areas where winds
are light. To the west of the ridge, a gale force low is tracking
northward across the far western Bering Sea, with a frontal
system extending north and east from the low center, then back
south across the heart of the Bering Sea (west of the Pribilof
Islands southward to Adak and Atka). Rain is falling ahead of the
frontal system, with colder more unstable air behind leading to
stronger and gustier winds behind the front.

&&

.MODEL DISCUSSION...
Models are in fair agreement through the next few days. The most
notable differences are track and strength of a series of short-
waves crossing the southern Alaska mainland Friday through
Saturday. Handling of these waves has also been inconsistent
between model runs. This makes sense, as models tend to struggle
with multiple short-waves in fast flow aloft. While there is high
confidence in the forecast for widespread snow across Southwest
and Southcentral Alaska the next couple days, the differences
noted created high uncertainty in total snow accumulation for any
specific location or region. Thus, expect to continue to fine-tune
snow amounts over the next 24 hours.

&&

.AVIATION...
PANC...Snow is expected to move in very late in the TAF period.
Right now timing indicates indicates it will start just after 00z.
Expect ceilings to drop to MVFR but vis will most likely be IFR in
snow.
&&

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

An upper level trough over the northern Mainland and a building
upper level ridge over the Bering are the two key features for
the next couple of days. Cold, northerly flow will arrive to the
area tonight as the upper level trough drops southward. Outflow
winds along the northern Gulf coast will increase overnight
tonight through Friday. Areas including Seward, Valdez, and the
Copper River Delta will all see elevated winds from the north and
generally gusty conditions. With the ridge to our west, gusty
outflow winds can also be expected through gaps and passes near
Kodiak Island, including Kamishak Bay, the Barren Islands, and
Shelikof Strait beginning late Friday and lasting through
Saturday. A front approaches from the west bringing a chance for
accumulating snow Friday night into Saturday. At this time,
accumulation of up to 3 inches is expected. As snowfall diminishes
by midday Saturday, a second, stronger upper level trough moving
southward late Saturday will allow cold air advection to continue
across the area through the weekend.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2: Tonight
through Saturday)...

A front moving into Southwest Alaska from the Bering tonight will
spell the end of the quiet weather and sunshine. As it moves into
the Kuskokwim Delta late this evening, snow will break out along
the coast before midnight, spread into Bethel after midnight, then
into Bristol Bay and the Lower Kuskokwim Valley in the predawn
hours Friday. During the day Friday, the eastward moving front
will rapidly weaken and fall apart. Thus, with the initial front,
snow totals will strongly favor locations farther west, which will
be advantaged by it both being night/earlier start time of the
snow (so the sun isn`t melting any of the falling snow), and the
front being stronger.

Behind the front Friday afternoon, onshore westerly to
southwesterly flow will allow the snow to persist on the west
facing slopes of the Alaska Range and Kuskokwim Mountains, with a
break for communities such as Dillingham and King Salmon.
Meanwhile, across the Kuskokwim Delta, while snowfall rates will
be much diminished during the day than during the morning, snow
showers will remain common in the onshore flow. On Friday evening,
a Bering low tracking along a front separating seasonably mild air
across Southwest Alaska and most of the Bering with a polar air
mass over northern and western Alaska will approach the Kuskokwim
Delta. Heavier snowfall will redevelop Friday afternoon across the
Kuskokwim Delta, which will continue into Friday evening as the
low center approaches. Snow showers will persist through the
overnight as the low moves inland. Behind the low, much colder air
on strong northerly wind flow will cause ocean-effect snow
activity to develop along the coast. Blowing and occasionally
heavily falling snow will reduce visibilities at times along the
coast into the day on Saturday. Meanwhile, upslope snow shower
activity will persist Friday night into Saturday along the Alaska
Range from King Salmon east. Snowfall rates will diminish area-
wide through the day Saturday, but snow shower activity could
persist into Saturday evening. Much colder air will overspread all
of Southwest Alaska by Saturday night, allowing temperatures to
fall to near zero in the Kuskokwim Valley, with single digits to
teens expected for overnight lows through Bristol Bay.

Snowfall totals in the Kuskokwim Delta from both events will total
in the 4 to 6 inch range, with isolated areas picking up as much
as 8 inches of new snow. The snow tonight will likely be wetter
and heavier in consistency. As the cold air moves in Friday night
into Saturday, the snow with this second batch will be a much more
powdery consistency. Thus, while more total snow is expected
tonight, the blowing snow threat is largely expected with the
second round of snow Friday night into Saturday. For the Lower
Kuskokwim Valley and Bristol Bay, 2 to 4 inches of snow are
expected, with the highest amounts along the foothills of the
Alaska Range.

&&

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

A low over the far western Bering and its associated front over
the central Bering are both moving eastward towards Alaska this
afternoon. The front will move into Southwest Alaska tonight.
Meanwhile the low will track between St. Lawrence Island and St.
Matthew Island Friday morning. High pressure will move over the
Aleutians through Friday night. It will strengthen over the
central Bering through Saturday night. A weak low will spread rain
over the central and western Aleutians Saturday evening.

The primary hazard under this pattern will be heavy freezing
spray, which will return to the eastern Bering along with much
colder air and gale force winds Friday night into Saturday. Strong
gap winds and freezing spray will impact the waters around the
Alaska Peninsula by Saturday, which will persist into Saturday
night.

&&

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

Gulf of Alaska...

Gale force gap winds are likely to continue into Sunday morning
south of Kodiak Island, out of the Barren Islands, and out of the
Copper River Delta. The winds will diminish Sunday afternoon,
with no gales expected from Sunday night through Tuesday. Freezing
spray may be common in windy areas with colder air moving into
the region.

Bering Sea...

There is high confidence that gale force winds will impact the
waters west of St. Matthew Island on Sunday. The winds will
diminish Sunday night. Gales are possible to the west of a low
that will track near the central Aleutians Tuesday. This is low
confidence however as there remains significant uncertainty with
the track and strength of the low. Heavy freezing spray and gale
force winds through the gaps south of the Alaska Peninsula are
likely to persist from Saturday night through the day Sunday.
Rapidly diminishing winds are expected late in the day Sunday,
ending this threat.

&&

.LONG TERM (Days 3 through 7: Sunday through Thursday)...

The long term forecast begins with good model agreement through
Sunday and Monday, followed by a loss of agreement and significant
uncertainty through the end of the week. The good news is that for
Sunday and Monday, there is good agreement that the weather will
be quiet across southern mainland Alaska. There is also good
agreement that we are in for a pair of much colder than normal
days as well. Cold air that moves in behind the low on Saturday
will dig in across the area on Sunday. This will keep gap winds
strong, especially across Southcentral, including around Kodiak
Island, the Copper Delta, Seward, and the Valdez marine areas.
Freezing spray, potentially heavy at times will be possible across
many of those same marine areas. As the low moves off and the high
to the west both weaken through the day on Sunday, all the winds
will diminish on Monday.

By Tuesday, the model agreement rapidly diminish regarding how
they handle a front over the Bering and a low over the Gulf, the
EC wants to keep both features stronger, lifting them moisture and
threaten coastal communities in both Southwest and Southcentral
with precipitation. Meanwhile the GFS is dry as the Bering front
dissipates and the low over the Gulf remains much further south.
Model agreement only diminishes further for Wednesday and beyond.

&&.
AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 155.
MARINE...Gale warning.. 132
150 155 165 180 181 185 412 414.
Heavy Freezing Spray...180 185
414.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...SB
SOUTHCENTRAL ALASKA...KO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JW
MARINE/LONG TERM...JW



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.