Gale Warning 696, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
510 PM AKST Mon Nov 13 2023

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3: This
afternoon through Thursday afternoon)...

With the vigorous upper level trough and its attendant surface
low exiting into the eastern Gulf of Alaska, snow has largely
tapered off across Southcentral Alaska. Lighter snow is
persisting across the Copper River Basin and Eastern Prince
William Sound but should taper off by late tonight. Even though
snow should end shortly, a Blizzard Warning remains in effect for
Thompson Pass through 9 PM. A tightening surface pressure
gradient is leading to gusty offshore gap winds, and gusts up to
50 mph through Thompson Pass are expected to cause a ground
blizzard as they resuspend fallen snow from earlier today. These
gap winds are expected to peak around midnight, then gradually
diminish as we head into Tuesday.

The first part of Tuesday should be relatively benign for the
Southcentral Mainland. There is a chance for areas of fog to
develop late tonight into early tomorrow morning in
Anchorage/Mat-Su as moisture moves from the recent snowpack into
the low-level atmosphere. Aside from a chance of snow showers
along the Talkeetna and Chugach Mountains, little to no
precipitation is expected.

From Tuesday evening through Wednesday evening, however, a strong
Bering Sea low will push its front across Southcentral and the
Gulf of Alaska. The highest precipitation amounts with this system
are expected in Susitna Valley and the mountains surrounding
Prince William Sound, with much lower precipitation amounts
expected at this time for parts of Kenai Peninsula, Anchorage, and
Matanuska Valley due to downslope drying. The lingering forecast
challenges with this system will involve precipitation type and
timing. While guidance is leaning towards snow, an influx of
warmer air through Turnagain Arm could lead to rain or a mix with
rain for Anchorage later on Wednesday. Overall, this storm system
is not expected to be as impactful as the last two for
Southcentral; while there is about a 60% chance that snow totals
in Susitna Valley could exceed a foot, this would come in the form
of lighter snow rates over the course of several days.

Peeking ahead at Thursday, upper level shortwaves rotating around
the Bering Sea low look to bring snow showers across Southcentral.
There remain some uncertainties with the timing of these waves
and, therefore, with the timing of precipitation.

-KC

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days
1 through 3: Today through Wednesday)...

The combination of cold air advection and upper level short-waves
rapidly tracking eastward across the Bering Sea will continue to bring
a showery regime to the Bering, Pribilof Islands, and into
Southwest Alaska. A transient upper ridge will build across
Southwest on Tuesday and briefly taper off showers before the next
system arrives Tuesday afternoon.

The next system will be a low that tracks from the Pacific to the
Aleutian chain this afternoon before it elongates and moves into
the Bering through Wednesday. The system's front will lift along
the Aleutians through Tuesday, reaching the Southwest Alaska
coast by Tuesday afternoon, and then the low itself will follow
and track across Southwest on Wednesday and Thursday. The front
will bring widespread rain across the Bering and Aleutians and
then a quick round of widespread snow to Southwest Tuesday evening
into Wednesday morning as it lifts to the east.

In general, gales will become widespread across the Bering and
Aleutians Tuesday into Thursday. The core of strongest winds
(sustained storm force with gusts to hurricane force) around the
southern periphery of the low is now advertised to track along
the coastal waters including the Central Aleutians Tuesday
evening through Wednesday morning. Winds will largely diminish
across the Bering and Aleutians later on Thursday as the expansive
system gradually weakens and tracks eastward across Southwest, as
mentioned above.

Confidence is high that winds across Adak and the central
Aleutians will increase to 45-60 mph through tomorrow evening.
However, confidence is not as high that gusts will reach 75 mph,
though wind gusts will easily flirt with 70 mph. Due to the
uncertainty, a watch has been hoisted, starting tomorrow evening,
and will last through Wednesday morning.

AF/SS

&&

.LONG TERM FORECAST (Days 4 through 7: Friday through Monday)...

The long term forecast period begins on Friday with a cooling
trend anticipated. Light to moderate snow should be ongoing across
the Copper River Basin and portions of Prince William Sound,
east, as an upper low shifts into Southeast Alaska into Saturday
night. The bigger story is an expected trough drifting into
interior Alaska. Which will pull a broad swath of colder
temperatures in from the north. At the same time a drier air mass
will help to clear out most precipitation for both Southwest and
Southcentral through the weekend. The exception will exist over
the Bering where isolated to scattered snow showers are forecast
with the trough's passage. A Kamchatka low then brings a strong
front into the Bering Sunday into Monday with potential high winds
as the front moves through the Western and Central Aleutians. The
front will progress into the eastern Bering by Monday with a
rain/snow mix and enhanced southerly winds along the front, from
the Eastern Aleutians up into the Chukchi Sea.

BL

&&

.AVIATION...

PANC...While skies have cleared this afternoon, there is a good
chance that stratus and/or fog with IFR conditions redevelops in
the Anchorage area as the sun sets. There is low confidence in
whether this will move over the terminal. At a minimum, with
westerly low level flow and some weak upper level short-waves
passing overhead tonight, do expect upslope clouds banked up
against the mountains. A shift to southerly steering flow on
Tuesday will help clear out anything that does form. The next
chance for snow and lower clouds/vis will then come late Tuesday
evening (after 06Z Wednesday).

Winds will remain light and variable through the TAF forecast
period.

&&

Preliminary Local Storm Report
National Weather Service Anchorage AK
1111 PM AKST Mon Nov 13 2023

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

0800 PM     Snow             Trapper Creek           62.32N 150.22W
11/13/2023  M12.0 inch       Matanuska-Susitna  AK   Trained Spotter

            A trained spotter measured 12 inches of
            snow. Storm total.

0800 PM     Snow             Amber Lake              62.17N 150.54W
11/13/2023  M5.0 inch        Matanuska-Susitna  AK   Trained Spotter

            A trained spotter measured 5 inches of snow.
            Storm total.

1230 PM     Snow             South Anchorage         61.12N 149.91W
11/13/2023  M13.1 inch       Anchorage          AK   Public

            A member of the public measured 13.1 inches
            of snow. Storm total.

0836 PM     Snow             Anchorage/Fairview      61.21N 149.86W
11/13/2023  E8.0 inch        Anchorage          AK   Public

            A member of the public estimated 8 inches of
            snow. Storm total.

&&