Gale Warning 837, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
502 AM AKST Sun Nov 17 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Tuesday night)...

Key Message:

* Clouds and areas of light snow will linger today, with clearing
  skies tonight through Monday.

* Cold and windy conditions are on tap for much of the region for
  the beginning of the work week.

A deep and cold trough is centered over mainland Alaska while an
upstream ridge builds over the western Bering Sea ahead of a deep
low tracking northward across the Sea of Okhotsk. This ridge will
play a key role in the weather ahead for Southcentral. In the
meantime, a short-wave trough is digging southeastward across the
central Gulf. An axis of moderate to strong cold air advection
behind this trough extends from Southwest Alaska and across
Kodiak Island and the Gulf. This is leading to widespread strong
and gusty winds, with peak wind gusts on the order of 50 to 65 kt
through bays and passes along the south side of the Alaska
Peninsula and out across the Kodiak Island coastal waters. An
upper level low which has been sitting over western AK is now
slowly dropping southward as the aforementioned upstream ridge
amplifies and builds eastward. A surface low continues to spin
over the northern Gulf, just south of Cordova. It is just beginning
to be pulled southward by the short-wave undercutting it to the
south. Areas of light precipitation are being observed in the
Cordova area northward to the Copper Basin. Very light snow,
mainly driven by cold air advection and upslope flow, lingers
in the Anchorage and Mat Valley areas up against the Chugach
Mountains. Though cold air advection over Southcentral is weak in
comparison with the western Gulf, it is combining with strong
pressure gradients to produce strong and gusty gap winds through
mountain passes and coastal bays. Air temperatures have not fallen
all that much since yesterday, largely due to the presence of
clouds and wind, but that will change.

The upper low over western Alaska will open into a trough and
track south across the Alaska Peninsula and down into the Pacific
on Monday. By this time, a now strong high amplitude ridge will
be centered over the Bering Sea and approaching mainland AK. This
will lead to deep northerly flow across the mainland, with deep
Arctic air settling over Southcentral. Despite the fact the
surface low in the Gulf will be exiting, pressure gradients will
continue to increase most places as a surface high builds from
western AK into the Interior. Thus, gap winds will strengthen and
move out into the valleys of Southcentral. The critical feature in
determining how strong the winds will be is a short-wave dropping
southward across the state on Monday. Model guidance varies with
the track and strength of this short-wave as it crosses Southcentral.
If the stronger scenario verified and it tracks southward into the
Gulf, would expect strong downward motion behind it to combine
with an increase in wind strength at all levels to lead to
potential for high winds of 75 mph or greater. Based on the most
envelope of solutions, the most likely location for this to occur
looks to be Thompson Pass down into Valdez. Secondarily, if it
tracks far enough west, the Matanuska Valley could see high winds.
Even the weaker and further east solutions will lead to an uptick
in winds Monday through Monday night.

Meanwhile, temperatures will steadily fall as we head through the
next few days. The winds will keep the actual air temperatures
from plummeting, but winds chills will drop well below zero for
nearly all of Southcentral. Winds will diminish most places
Tuesday though Tuesday night as the upper ridge builds in from
the west. THis could mean that Wednesday morning ends up being
the coldest morning of the week.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA AND THE BERING
SEA/ALEUTIANS (Days 1 through 3)...

Synoptically, a low over the Chukchi Sea will continue to bring
waves of moisture southward toward the Aleutians and Alaska
Peninsula through this afternoon. Dry, arctic air will begin to
invade Southwest Alaska Sunday night causing subzero temperatures
in the interior Monday afternoon through Tuesday morning. Finally,
a ridge of high pressure builds into the Aleutians during the
weekend reaching the Alaska Peninsula and Southwest Alaska
Tuesday.

Current nighttime microphysics shows convective snow showers
continuing to flow southeastward over the Bering Sea toward the
Eastern Aleutians and the Alaska Peninsula this morning. Surface
observations in Cold Bay and Dutch Harbor shows 12-hour
precipitation amounts ranging from 0.10" in Cold Bay to 0.03" in
Dutch Harbor as of 4:00am today. Through today, numerous snow
showers will reach locations east of Cold Bay and continue through
the afternoon hours. Northwest winds ranging from 30 to 40 mph
with higher gusts out of bays and passes are expected through
tomorrow evening. The greatest winds are likely this evening
through tomorrow morning as a shortwave moves over the Alaska
Peninsula causing wind gusts to briefly reach 50 mph. Winds will
shift more northerly early tomorrow morning.

Arctic air will flow into the Interior this evening through
Tuesday morning with many places in the Interior staying below
zero Monday afternoon through Tuesday morning. Guidance continues
to show the coldest air will be during the late Monday evening to
the late Tuesday morning hours. This will coincide with a mostly
clear sky too. Therefore, Tuesday morning's lows ranging from the
middle 20s to the middle teens below zero will be wide spread from
Aniak to Lime Village northward. Wind chills ranging from the
middle -20s to the middle -30s are expected during this time too
in this area. South of this line, including Bethel and
Dillingham, lows drop to the single digits above and below zero
will be common.

A ridge of high pressure moves over the Aleutians this weekend
bringing temperatures into the 40s, fog and rain showers. This
warm air moves over the Bering Sea, Alaska Peninsula and
Southwest by Tuesday afternoon quickly rising temperatures into
the 20s in the AK Pen, the 30s along the Southwest coast from
Goodnews Bay northward and above zero in the Interior. Widespread
fog will be common, too.

-DJ

&&

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

By Wednesday, high amplitude ridging pushing in from the Bering
Sea/Aleutians will cover the majority of the state, bringing
northerly flow to most of southern mainland Alaska. Warmer air
from the Pacific is associated with this feature, so we are
expecting the cold temperatures from the first half of the week to
give way to more moderate temps, especially for the Southwest.

A North Pacific low looks to enter the Bering Sea Thursday night,
tightening the pressure gradient and bringing moderately strong
southerly winds to the Western Aleutians and Central Bering Sea.
This system will be pushed to the northeast as it moves through
the top edge of the amplified ridge. The low center should stay in
northern Alaska, but there is some model disagreement here about
how much it will flatten out the ridge. This will be something to
keep an eye on going forward as it could potentially impact
Southcentral.

Light winds and little precipitation are expected throughout the
long term outlook for most of Southcentral and Southwest Alaska.

&&.AVIATION...

PANC...Light snow in the vicinity will finally taper off today as
the upper trough overhead sinks southward into the Gulf and colder
and drier air continues to advect into the region. This will allow
ceilings to slowly lift, with clearing skies likely sometime
tonight. The bigger forecast challenge will be winds. The terminal
will sit right on the eastern periphery of gusty northerly winds
coming from the Susitna Valley into northern Cook Inlet. Suspect
gusts will be in and out at the airport for much of today. Overall
strengthening of the winds with time will lead to gusts becoming
more frequent this afternoon through tonight.

&&

Preliminary Local Storm Report
National Weather Service Anchorage AK
1135 AM AKST Sun Nov 17 2024

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

0800 AM     Snow             8 SE Eagle River        61.23N 149.44W
11/17/2024  M11.2 Inch       Anchorage          AK   Public

&&

Preliminary Local Storm Report
National Weather Service Anchorage AK
1138 AM AKST Sun Nov 17 2024

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

0828 AM     Snow             3 E Eagle River         61.31N 149.48W
11/17/2024  M12.5 Inch       Anchorage          AK   Public

&&

Preliminary Local Storm Report
National Weather Service Anchorage AK
1139 AM AKST Sun Nov 17 2024

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

1017 AM     Snow             2 SE Eagle River        61.30N 149.53W
11/17/2024  M9.0 Inch        Anchorage          AK   NWS Employee

&&

Preliminary Local Storm Report
National Weather Service Anchorage AK
1144 AM AKST Sun Nov 17 2024

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

0800 AM     Snow             8 SE Eagle River        61.23N 149.44W
11/17/2024  M11.2 Inch       Anchorage          AK   Public

            Storm total. Corrects previous snow report
            from 8 SE Eagle River.

&&

Preliminary Local Storm Report
National Weather Service Anchorage AK
302 PM AKST Sun Nov 17 2024

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

0154 PM     Snow             Sutton                  61.71N 148.87W
11/17/2024  M3.5 Inch        Matanuska-Susitna  AK   Trained Spotter

            Updates previous report from Sutton. Since
            last evening on the 16th, an additional 1.25
            in of snow has fallen.

&&

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
340 PM AKST Sun Nov 17 2024

AKZ112-181500-
Matanuska Valley-
Including the cities of Palmer, Wasilla, Sutton, and Chickaloon
340 PM AKST Sun Nov 17 2024

...AREAS OF BLOWING SNOW EXPECTED TO REDUCE VISIBILITY ALONG THE
GLENN HIGHWAY MONDAY and MONDAY EVENING...

The last storm system dropped 3-6 inches of light and fluffy snow
across parts of the Matanuska Valley. This low density snow on
the ground will be very transportable when the Matanuska Valley
wind ramps up on Monday. Gusty winds coming out of the Mat Valley
will begin to increase this evening, but the peak gustiness of
winds will be in the 30 to 50 mph range on Monday afternoon and
evening. Expect places such as the Palmer Hay Flats may see
visibility reduction to one-mile or less at times during the
evening commute.