High Wind Warning 14, NWS Anchorage, AK

356 
WWAK72 PAFC 221458
NPWALU

URGENT - WEATHER MESSAGE
National Weather Service Anchorage AK
558 AM AKST Thu Dec 22 2022

AKZ181-221600-
/O.EXP.PAFC.HW.W.0014.000000T0000Z-221222T1500Z/
Alaska Peninsula-
Including the cities of Cold Bay and Sand Point
558 AM AKST Thu Dec 22 2022

...HIGH WIND WARNING WILL EXPIRE AT 6 AM AKST EARLY THIS
MORNING...

Gusty easterly winds have fallen below warning criteria and are
expected to continue to slowly diminish through the day.

$$

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

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
612 PM AKST Wed Dec 21 2022

.ANALYSIS AND UPPER LEVELS...

A strong blocking ridge is centered over the Chukchi Sea and
extends down over northern Alaska. A second ridge extends from off
the western coast of the CONUS northwestward to the eastern Bering
Sea. A narrow trough is getting squeezed between the two ridges
over southern Alaska. Most of southern Alaska remains entrenched
in a deep chill, with temperatures bottoming out at -20F to -35F
degrees over the Copper River Basin and Kuskokwim Valley and
single digits below zero to single digits above zero for most
of the rest of Southwest and Southcentral Alaska.

Meanwhile, a long-wave trough is positioned over the North Pacific
and southern Bering Sea. A deep surface low about 500 miles
southeast of Unalaska is lifting slowly northward, with a leading
occluded front approaching the eastern Aleutians, Alaska
Peninsula, and Kodiak Island. A stationary front remains in place
across the southern Bering Sea down to the Eastern Aleutians and
southern Alaska Peninsula. CIMMS MIMIC Precipitable Water
satellite products indicate a moisture rich environment across the
aforementioned areas, with 0.60" to 1" Total Precipitable Water
which is roughly 200% of normal for this time of year. This is
leading to areas of heavy rain, especially across the Eastern
Aleutians and Unalaska areas where a Flood Warning remains in
effect for urban and small stream flooding. The Unalaska (Dutch
Harbor) Airport recorded in excess of 6" of rain in the past two
days. With strong high pressure over northern Alaska and the
northern Bering Sea, pressure gradients are particularly tight
across the region. As a result, there is a large area of gale to
storm force winds extending from the Gulf of Alaska across the
Alaska Peninsula and much of the Bering Sea.

The entire upper trough and storm system is lifting slowly
northward toward southern Alaska. This is tightening pressure
gradients further across southern Alaska leading to gusty offshore
winds in many places. Precipitation lifted north to Kodiak Island
last night the form of snow, but changed to rain this morning as
warmer air arrived with the approaching frontal system. Lastly,
there is some light snow pushing onshore of the north Gulf coast
and Prince William Sound, primarily due to overrunning and upslope
flow.

&&

.MODEL DISCUSSION...

Model guidance is in decent agreement with larger scale features
through Friday. Differences then develop with the short-wave
driving southwestward across southern Alaska Friday night and the
resultant cyclogenesis somewhere over Southwest Alaska/eastern
Bering Sea Saturday night/Sunday. This could be an impactful
storm, but model spread is quite large and will need to await
future model runs to hone in on which areas will be impacted by
this system. Model spread also grows over the Gulf of Alaska
Friday night and Saturday with systems moving up from the
Pacific and across the Gulf. This will affect the wind and
precipitation forecast along the Gulf coast. In summary, forecast
confidence is average to above average through Friday, then low
beyond that.

&&

.AVIATION...
PANC...Increased pressure gradients and low level winds have
ended any threat of fog and low clouds. Northerly winds will
hold fairly steady below 12kts until Thursday night/Friday when
stronger northerlies will develop as cold air advects across the
region.

&&

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

Mostly clear skies and well below temperatures will likely
persist for the rest of the week across the southern mainland. A
front extending ahead of a North Pacific low continues to push
northward toward the north Gulf coast. Areas of light snow will
persist tonight across the eastern Kenai and western Prince
William Sound mountains before tapering off Thursday morning.
Otherwise, most the precipitation will stay south of Prince
William Sound.

Over the coastal waters, increasing easterly winds associated the
front will reach to storm force with hurricane gusts possible
sometime tonight into Thursday morning. There remains some model
disagreements with the track and position of the low over the
Gulf, but winds are expected to slowly decrease to gales sometime
on Friday.

Meanwhile, an upper level trough from the Arctic will drive
southwestward across Southcentral Thursday night and Friday. This
will bring colder air towards the Copper River Basin along with a
tightening pressure gradient between a surface high across
northern Alaska and a low pressure system across the southern
Gulf. Strong winds across the Matanuska Valley with gusts up to 65
mph begins Thursday night and continues into Friday evening. The
main concern is blowing and snow drifts onto roads that may
produce hazardous travel conditions with a reduction to visibility
(please see our Winter Weather Advisory for more details). Winds
will then slowly diminish Friday evening into Saturday. Cold wind
chills are also expected for the Copper River Basin from Thursday
night to Friday evening. Heading into the weekend, the
aforementioned North Pacific low may bring a return of snow across
Southcentral, but details are still being ironed out so stay
tuned.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: This
afternoon through Saturday afternoon)...

An upper-level low in the vicinity of the Yukon Valley, continues
to elongate and weaken as heights build slightly into Southwest
Alaska. Temperatures tonight will be warmer than the last few
nights area wide as a North Pacific low and its associated front
lift northward towards the eastern Aleutians overnight tonight
into Thursday morning. The Alaska Peninsula (AKPEN) stands the
best chance to see precipitation from this system through tomorrow
evening in the form of a mix of rain and snow as the system moves
into the Bering Sea and southeasterly upslope flow continues.
There is also the chance that coastal sections of Bristol Bay and
the Kuskokwim Delta could see some light snow showers from this
system Thursday morning into the afternoon; amounts are expected
to light if any. Colder air works back into the area for Friday
and Saturday with mostly quiet weather conditions. There is some
uncertainty for Friday afternoon into Saturday, as guidance is
struggling with how to handle a westward ejecting shortwave off of
an upper-level trough over northern Yukon and where a potential
low pressure system spins up in response. As of now, most
precipitation looks confined to the AKPEN and coastal Bristol Bay
through Saturday morning as the system pulls westward towards the
eastern Aleutians Saturday afternoon. Stay tuned to the latest
forecast updates as details become more clear for the second half
of Friday into the day on Saturday. The overall trend is for a
more active AKPEN and a quieter mainland Southwest.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3: This
afternoon through Saturday afternoon)...

The Aleutian Chain, Bering Sea, and Pribilofs will continue to be
active in the weather department for the short-term period. An
atmospheric river continues to reorient itself from north/south to
northwest/southeast. It is this system that is causing continued
flooding in Dutch Harbor/Unalaska and a Flood Warning remains out
until Friday morning. The heaviest rain over the central to
eastern Aleutians will taper off Thursday morning into the
afternoon as the low pressure system moves over the Chain and
westward into the Bering Sea. The Pribilof Islands will continue
to see a rain/snow mix and switching to all snow at times through
Friday afternoon. Dynamic cooling from precipitation intensity
stemming from the atmospheric river and the Bering system moving
westward is the reason why the Pribilofs temperatures remain on
the cooler side. Gusty conditions also continue throughout the
central and eastern Bering as a belt of easterly storm-force
winds is generated early Thursday morning through Thursday
afternoon on the Bering side and Pacific side of the Alaska
Peninsula when the North Pacific low and its front lifts north
towards the eastern Chain. Winds diminish back down back down to
gale-force late Thursday afternoon through the rest of the short-
term. There is uncertainty towards the end of the short-term
though as guidance is struggling on handling a westward ejecting
shortwave from an upper trough over the Yukon Territory and where
exactly a surface low spins up in the eastern Bering or along the
Aleutian Chain itself. Stay tuned to the latest forecast updates
as details continue to be fine-tuned regarding the evolution of
this system.

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

It is becoming more clear that an upper level low will split off
of the cold trough over the mainland part of the state and set up
over the Eastern Aleutians/Alaska Peninsula by Sunday. Once this
upper level pattern is established, it will not change much
through the middle of next week. The result will be temperatures
generally returning to more seasonal levels with it colder in the
Bering Sea region and warmer over mainland Southern Alaska.

A surface low should be in that eastern Aleutian/Alaska Peninsula
region vertically stacked with the upper level low early through
middle of the week. This will not be a strong low but will keep
some clouds and precipitation in the area. The strongest low early
next week will be in the Gulf of Alaska Sunday into early Monday.
While most of the coast will see this precipitation in the form
of snow, areas around southern Prince William Sound may have
periods of rain. We will just have to watch the development of the
storm to see whether the warmer temperatures make it to the coast
or not.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Warning 185.
Winter Weather Advisory 111 141.
MARINE...Heavy Freezing Spray 127 130 139 140 180 181 185.
Storm 130 131 132 138 150 155 160 165 179 180 185 351 352 414
Gale 119 120 127 128 136 137 139 141 170 171 172 181 411 412 413.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SB
SOUTHCENTRAL ALASKA...MF
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DN
LONG TERM...EZ