Gale Warning 711, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
519 AM AKST Sun Nov 19 2023

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...

The coldest morning of the season thus far is currently underway
across much of southcentral Anchorage. Temperatures have dropped to
the -10 to -20 range across much of the Copper River Basin and
Susitna Valley. The Matanuska Valley is marginally warmer with
temperatures ranging from about 0 to -10 as of 4am. Temperatures
across much of the western Kenai Peninsula range from about -10
below to 10 above. That same range of about -10 below to 10 above is
also the story for Anchorage overnight.

Satellite imagery shows a mostly clear sky across the forecast area
thanks to an amplifying ridge. Low stratus and freezing fog has
developed across the Anchorage Bowl and over the Knik Arm. This area
has been sloshing between the Knik Arm / Eastern Anchorage and
Western Anchorage through the night. Temperatures warm a few degrees
as the fog/stratus moves over, but then drops once again to below 0
when the fog clears the area. This fog should be slow to
dissipate today given minimal horizontal air movement
/ wind, along with limited diurnal heating and mixing thanks to a
low sun angle. A fog advisory is in effect through noon today, but
may have to be continued into Monday should no improvement be
realized.

Otherwise, the amplifying ridge will lead to clear, cold, and dry
weather across much of southcentral Alaska Sunday into Monday. By
late Monday, a large low will begin to move northward into the Gulf
of Alaska. Increasing pressure gradient between the ~965mb low and
high pressure across much of Alaska and YT will result in winds
increasing throughout much of southcentral Alaska. A winter storm
watch for blizzard conditions has once again been hoisted for
Thompson Pass as wind gusts upwards of 55mph will result in greatly
reduced visibility for that portion of the Richardson Highway. Winds
are expected to also increase through Valdez, but lesser fresh snow
contribution will help mitigate visibility issues.

In addition to Thompson Pass and Valdez, winds will pick up across
the board. Gusty northeast winds are expected out of the Matanuska
River Valley through Palmer+Wasilla and down the Knik Arm to western
Anchorage Monday/Monday night. Gap winds will also pick back up out
of the Copper River delta and other various gaps. Marine areas will
see fairly widespread gale force winds, with many small crafts
closer to the coast and storm force across the open waters of the
Gulf of Alaska.

The strength of the low will diminish as it approaches the coast on
Tuesday, with winds subsiding as a result. Precipitation will begin
as early as Monday evening/night for some coastal communities such
as Cordova and the adjacent mountains. Snow is likely at onset, but
robust warm air advection in the low/mid-level should force a
switchover to rain in any lower elevations. Precip will be limited
outside of the immediate Gulf of Alaska coast and Chugach Mountains
as the northward progression of the low slows. Temperatures Tuesday
will be closer to average as that cold air gets displaced.

-Brown

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today
through Tuesday night)...

Cold and mostly dry conditions will continue for Southwest Alaska
at least into the first half of the week, as surface high pressure
extending up from the eastern Bering Sea remains in place through
Monday morning. The one exception to the dry conditions is another
band of light snow showers, similar to yesterday's, sweeping
eastward across the Kuskokwim Delta this morning. This light snow
is not likely to produce any significant accumulation in the
region, and will move into the Lower Kuskokwim Valley later this
morning. Isolated to scattered snow showers will continue to
stream into the Delta region off the Bering Sea today until winds
shift out of the southeast tonight as the surface high pressure
begins to retreat into the Interior. Expect drier conditions
thereafter.

A widespread deck of stratus over much of inland Southwest Alaska is
keeping temperatures generally warmer this morning, and this cloud
layer is anticipated to stick around through the day. It may begin
to scour out tonight with the retreat of the surface high allowing
northeasterly flow to bring in drier air over Bristol Bay. This
will cause another round of colder low temperatures Sunday night.
Models begin to diverge for Monday night, however, as warmer air
and potential layer of insulating high-level clouds moves in off a
low moving into the Gulf of Alaska, which may keep low
temperatures warmer for Bristol Bay and the Lower Kuskokwim
Valley. However, clearer skies to the northwest could allow the
Kuskokwim Delta to see a night of low temperatures dropping into
the single digits. Regardless, temperatures remain below normal
through at least Tuesday.

CQ

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3: Today
through Tuesday night)...

A storm force low centered just east of the Kamchatka Peninsula is
pushing a front with strong, intensifying winds and heavy rain
into the western Bering Sea this morning. The front has already
passed east of Shemya, where winds have already diminished below
high wind criteria. The front pushes into the central Aleutians
today, where wind gusts up to 70 mph for Adak, and wind gusts up
to 65 mph for Atka, are expected. By this evening, the low
occludes and its associated winds begin to diminish gradually as
the front continues further north and east. At the same time, a
second round of winds begin to move into the western Aleutians.
Colder air wrapping around the south side of the low will
contribute to an unstable atmosphere, where there will be a low
potential for wind gusts up to 75 mph mix down to the surface at
Shemya.

By Monday morning, the strongest core of winds moves into the
northern Bering Sea and weakens below storm force. Rain begins on
the Pribilof Islands as the low draws enough warm air northward
for liquid precipitation. Some colder air lingers longer near the
eastern Aleutians, which may allow for a light rain/snow mix,
though most of the precipitation is likely to be downsloped out
for Unalaska until the main brunt of the front arrives Monday
afternoon, by which time the atmospheric profile is warm enough
for precipitation to fall as rain. After this point, the front
rapidly weakens and precipitation tapers off through Monday night.

Another storm force low tracks south of the Aleutians Monday
night, bringing gale force easterly winds and another round of
moderate to heavy rain to the western Aleutians. The front pivots
across the central Aleutians for Tuesday, spreading precipitation
and gale force winds eastward. Further north across the Bering
Sea, easterly winds begin to intensify going into midweek.

CQ

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

There continues to be high confidence in active weather across
Southern Alaska and the Bering Sea during the extended period,
with forecast confidence hovering around average. The primary
hazard being monitored is the potential for heavy precipitation
along Eastern Kenai Peninsula and Prince William Sound from
Wednesday through Friday. Otherwise, the weather looks active (but
fairly seasonable) for this time of year.

With a low in the Gulf of Alaska moving onshore through early
Wednesday morning, the primary weather maker in the extended
period will be a low moving along the Aleutian Chain. Current
guidance continues to drop minimum sea level pressure to about
940-950 mb, increasing our confidence in the strength of this
feature. Guidance also continues to show sustained winds to storm
force around the backside of the low, as well as a short period
of sustained winds up to storm force along the low's front.
Overall, shifts in the low track look to keep storm force winds
largely south and west of the forecast area, though they still
remain within the realm of possibilities.

While the low itself will remain near the Aleutian Islands/Bering
Sea, its front will sweep out ahead of it and bring the bulk of
impacts to the Southern Mainland through Thursday. Expect winds to
gale force along this front and for abundant moisture to sweep
across the region. While the front will move rather quickly inland,
precipitation rates could be high along Western Susitna Valley
and the north Gulf coast as the front moves in, and southerly flow
behind the front could lead to persisting precipitation along
coastal mountains after the front has passed. 850 mb temperatures
approach freezing as warm air advects inland with this front,
raising questions about what precipitation type we'll see.
Coastal locations are most likely to see rain, though
precipitation type remains uncertain further inland. Rain, snow,
and even freezing rain remain on the table, so stay tuned as we
continue to evaluate this aspect of the forecast.

Otherwise, model guidance continues to differ with the track of
this low as it occludes on Thursday. The long-term forecast leans
towards the scenario where ridging is stronger behind the low,
leading to this low moving across the Aleutians into the Bering
Sea. The other scenario keeps the low south of the Aleutians, with
implications for wind directions/speed along the Aleutian Chain
and precipitation in Southwest Alaska. Downstream differences
between these two scenarios worsen into Saturday, where the low
position eventually affects the location of a plume of moisture
headed for Southcentral Alaska and the track of a front moving
into the Bering Sea from the west.

-KC

&&

.AVIATION...

PANC...Areas of low stratus and fog will likely continue to drift
in and out of the terminal through most of the day today and
potentially persist well into tonight. Ceilings and visibility
will vary from as good as VFR at times as breaks in the
fog/stratus develop, to IFR or even LIFR as dense fog and very low
stratus move into place. Winds will remain light, but should
begin to pick up slightly from the north by Monday morning. These
winds should begin to mix out lingering low clouds and fog and
result in more consistently improving conditions near the end of
the TAF period.

AS

&&

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
1239 PM AKST Sun Nov 19 2023

AKZ102-121-201500-
Anchorage-Western Kenai Peninsula-
Including the cities of Anchorage, Eagle River, Indian, Eklutna,
Kenai, Soldotna, Homer, and Cooper Landing
1239 PM AKST Sun Nov 19 2023

...GUSTY WINDS ALONG KNIK ARM AND COOK INLET MONDAY...

Strong northerly winds with gusts between 25 and 50 mph will
develop through the day Monday along Knik Arm and Cook Inlet. For
the Anchorage Municipality, this includes areas west of the Glenn
Highway, Downtown, and west Anchorage. For the western Kenai,
areas from Nikiski south to Anchor Point will receive similar
winds. Most of the snow in the Anchorage area has hardened due to
recent rain and warm temperatures, but areas of blowing and
drifting snow are possible. For the western Kenai, recent dry snow
will be easier to transport, resulting in a higher likelihood of
blowing and drifting snow. Despite warming temperatures, wind
chills will range between -10F and 5F.