High Wind Warning 16, NWS Anchorage, AK

085 
WWAK72 PAFC 191402
NPWALU

URGENT - WEATHER MESSAGE
National Weather Service Anchorage AK
502 AM AKST Sun Nov 19 2023

AKZ191-191515-
/O.EXP.PAFC.HW.W.0016.000000T0000Z-231119T1400Z/
Western Aleutians-
Including the city of Shemya and Amchitka
502 AM AKST Sun Nov 19 2023

...HIGH WIND WARNING HAS EXPIRED...

Winds have diminished across the western Aleutians as the
strongest winds have pushed into the Bering Sea. Another round of
winds which may gust as high as 70 mph is forecast later this
evening before diminishing Monday morning.

$$

For more information from the National Weather Service visit
https://weather.gov/afc

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
517 AM AKST Sat Nov 18 2023

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

Key Takeaways:

1) The coldest air of the season has arrived and will persist
through the weekend and into Monday. Expect overnight lows ranging
from 10 to 15 above zero along the coast, from 10 below zero to 5
above zero from Cook Inlet to the Mat-Su Valleys, and 25 below to 10
below zero for the northern Susitna Valley and Copper River Basin.

2) Strong northerly gap winds will continue along the coast from
Seward to Whittier and Valdez through Sunday. Blizzard conditions
will continue for Thompson Pass through today. Elsewhere, areas of
blowing snow are also possible along the coast of Prince William
Sound and Turnagain pass.

GOES water vapor imagery shows broad upper-level troughing persists
across southcentral/eastcentral Alaska. The primary wave axis
rotating around the broad trough and associated surface low has
pushed into the eastern Gulf, with shower coverage diminishing
across the eastern/coastal Chugach. Remnant moisture and light
northnorthwest flow in the mid-levels has continued to bring low/mid-
level cloud cover for parts of Anchorage, the eastern Mat-Su Valley,
and the adjacent Chugach Mountains. This has resulted in overnight
temperatures being somewhat warmer than they would have been
otherwise, and a solid 5-10 degrees warmer than cloudless locations
on the periphery of this cloud cover.

As the trough continues east today, ridging will amplify across the
interior Southcentral while a surface low remains in the northern
Gulf. Gap winds will continue to intensify, especially for mountain
passes and gaps along the coast. These winds will peak by early
afternoon today for Seward and Whittier, with the peak of winds
arriving late this evening for Valdez and Thompson Pass. The
combination of recent snow from Whittier to Valdez will result in
some blowing snow through Saturday with blizzard conditions expected
for Thompson Pass.

Temperatures will also continue to fall as 850 mb temperatures fall
to near -20C through the weekend. This will result in the coldest
temperatures so far this season.

Winds and coastal precipitation will likely return by late Monday as
frontal system moves into the northern Gulf.

-Brown

&&

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

Conditions will remain colder than normal and relatively calm
across Southwest Alaska this weekend under the influence of
surface high pressure. This will be punctuated today by a weak
shortwave over the Kuskokwim Delta, producing a line of light snow
showers pushing east into the Lower Kuskokwim Valley this
afternoon and evening, before weakening. A trace to an inch of
snowfall is possible from this feature through tonight, from
Bethel north and east to Aniak. Temperatures will remain below
normal through at least Monday under increasingly clear skies and
with the current cold air mass remaining in place. Calm, quiet
conditions also extend across the Bering Sea/Aleutians today as a
result of a ridge out ahead of an incoming deep low. Scattered
ocean effect snow showers will continue to drift into the
Aleutians and Alaska Peninsula, enhanced by an upper level
shortwave crossing the eastern Bering Sea today and exiting into
the North Pacific by tonight.

Attention from there shifts to a deep 940s mb low near the
southern tip of the Kamchatka Peninsula, which sends an
intensifying front into the western Bering Sea and Aleutians
tonight. Sustained winds well into storm force range move into
the western Aleutians tonight, increasing to near hurricane force
as the front progresses north and east into the Bering Sea. With
the front intensifying as it crosses Shemya late tonight, the
question of whether or not high winds will be experienced there
depends strongly upon the track of the low, hinging on minor
changes in its forward speed. With that taken into consideration,
there continues to be a moderate chance for winds to gust to 75
mph or greater at Shemya. Therefore, a High Wind Watch remains in
effect for the western Aleutians.

The front continues east on Sunday, into the central
Aleutians/Bering Sea. The main core of winds is forecast to pass
north of the island chain. This, combined with the unfavorable
southerly wind direction and atmospheric profile has led to the
cancellation of the watch for the central Aleutians. Regardless,
strong wind gusts as high as 65 mph are still anticipated there.
Sunday evening, a second round of high winds have the potential to
push through the southwest corner of the Bering as the parent low
passes to the west. However, the low will be occluded by this
time, and winds associated with the low will begin to diminish. A
lot of warmer air and precipitable water is associated with this
low and rainfall could be heavy at times.

The low traverses the far western Bering Sea on Monday as it
tracks north, winds gradually weakening. The strongest core of
winds moves into the northern Bering and weakens below storm force
by Monday morning. The low's occluded front pushes to the
Pribilof Islands and the eastern Aleutians, bringing air warm
enough on southerly flow for precipitation to fall mostly as
rain. Another low, likely storm-force, looks to approach the
western Aleutians by Monday night.

CQ

&&

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

High confidence in active weather across Southern Alaska and the
Bering Sea for the long-term, though confidence remains low in the
finer details at this time due to model uncertainty. Here are the
hazards being monitored for this time period:
* Heavy precipitation along Eastern Kenai Peninsula and Prince
  William Sound from Tuesday through Thursday
* High winds across much of Southcentral Alaska from Monday into
  Tuesday

Tuesday begins with a 960-970 mb low moving north into
Southcentral Alaska. Some differences persist with timing and low
position, but there remains a consistent signal for sustained
winds at storm force (>= 50 kt) extending across much of the
northern Gulf coast, from Cordova in the east to Kodiak Island in
the west. Gusts could reach as high as hurricane force (>= 65
kt). In addition to strong winds along the front, a tightening
surface pressure gradient between a 1020-1030 mb interior Alaska
high and this incoming low could contribute to gusty gap winds
prior to the arrival of this front, likely through Matanuska
Valley and Thompson Pass. These bear watching, especially as
residual cold air in the Copper River Basin could lead to a bora-
type wind event. Speaking of cold air, some uncertainty remains
with precipitation type as abundant moisture streams in with this
front. Will temperatures stay below freezing as this weekend's
cold air takes longer to scour out? Or could warm air advection
lead to mixed precipitation? Overall, while the position of the
low will have some effect on precipitation amounts, there seems to
be a decent downsloping signature, suggesting that much of the
precipitation will be focused along the north Gulf coast mountains
with not much making it inland into the primary Southcentral
population corridor.

Overall, the general trend for the long-term will include a warm-
up as the aforementioned Southcentral low moves in from the south
and an occluded low moves towards Western Alaska from the Bering
Sea. This warm-up will be further enhanced with the movement of
yet another low towards the forecast area by Tuesday. A North
Pacific low (with current guidance pointing towards minimum sea
level pressure of 940-950 mb) moves along the Aleutian Chain from
Tuesday through Friday. Model discrepancies with the positioning
of this low means that wind directions and speeds are difficult to
pinpoint at this time. However, operational guidance is pointing
at sustained winds of at least storm force (and perhaps even
hurricane force) for the Bering Sea and Aleutian Islands. It's
too early yet to delve into the forecast details. However, the
outlook is for strong winds along the Bering and Aleutians, and
for elevated winds (up to gale force) and abundant moisture to
sweep across Mainland Alaska along the low's front. Precipitation
type, again, will be something to watch as this front further
warms temperatures.

- KC

&&

.AVIATION...

PANC...VFR conditions and light northerly winds will persist.
Temperatures are expected to drop into the single digits during
the overnight hours this weekend.

KM

&&