Gale Warning 760, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
531 AM AKST Tue Nov 29 2022

.ANALYSIS AND UPPER LEVELS...

Very cold, clear and dry conditions have taken hold across most
of Southcentral as well as a strong ridge continues to amplify
over the Bering and western mainland. Gusty outflow winds are
continuing out of gaps and bays along the northern Gulf coast and
Prince William Sound, including near Whittier, Seward and Valdez.
The strongest winds have been focused through Thompson Pass and
Valdez, where the strongest pressure gradient exists between the
frigid air over the Copper River Basin and warmer air out over
water. Where winds overnight have remained mostly calm, ideal
circumstances for radiative cooling have allowed temperatures to
drop into the -10s to low -20s overnight, including near Kenai,
Willow, and Gulkana. Temperatures are slightly warmer over
Southwest, but readings a few degrees below zero are still common
away from the immediate coast. Much warmer conditions exist across
the Bering and along the Aleutians underneath the ridge axis,
with surface temperatures mostly ranging between the upper 30s to
upper 40s. A blanket of low marine stratus remains trapped under
the ridge as well, with fog intermittently affecting parts of the
Pribilofs and Aleutians.

&&

.MODEL DISCUSSION...

Model agreement remains very good for the pattern progression and
for noteworthy features through the end of the work week. Some
slight timing differences still exist for the potent trough
expected to move southeast across Southwest and Southcentral
between Wednesday and afternoon and early Thursday morning, but
the overall impact to the forecast remains minimal. The above
average model agreement persisting through the end of the week
supports generally high forecast confidence at this time.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Tuesday through Thursday night)...

Southcentral remains sandwiched between an upper-level low over
the Alaska Panhandle and a ridge extending from the North Pacific
up along the west coast of the state. The resultant northerly flow
continues to usher in colder and drier air, with generally clear
skies and below normal temperatures prevailing. The cold air
advection and northerly flow are maintaining gusty offshore winds
which are expected to peak this morning before slowly diminishing
through the late afternoon and evening hours as the ridge slides
east and both the cold air advection and northerly flow wane.

The next big weather feature to impact the region is a surface
low and associated upper-level wave parked over eastern Siberia
this morning. These features will quickly move east, making it to
around Norton Sound Wednesday morning. The surface low and its
front will weaken as they advance on toward the Alaska Range by
Wednesday afternoon; however, the upper-level wave will continue
to track east and move over Southcentral by late Wednesday
afternoon. Southwesterly flow ahead of the decaying front and
upper-level trough axis will advect moisture into the region,
allowing for increasing clouds and the chance for widespread light
snow moving from west to east. This system will move quickly
east, though, and with plenty of cold, dry air in place near the
surface, valley locations may only see flurries to, perhaps, a
dusting of snow. At higher elevations, especially along the
western facing slopes of the mountains, a couple of inches of snow
could fall before the system moves to the Copper River Basin for
Wednesday night into Thursday morning.

As this system departs, the ridge / trough pattern that is
currently affecting the region will set up once again. This
pattern will allow for cold air to advect back in behind the
trough with gusty offshore winds quickly ramping up for favored
gap locations and mountain passes Thursday morning through
Friday.

&&
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...

The pattern will become more active on Wednesday as a frontal
system moves through the area. The biggest forecast challenge with
respect to this frontal system is precipitation type. There is
good model agreement that 850 mb temperatures will be above
freezing across the Kuskokwim Delta and Bristol Bay during frontal
passage. Meanwhile surface temperatures will still remain below
freezing across most of the area except for the immediate coastal
areas. Due to this set up, freezing rain is likely across the
Kuskokwim Delta Wednesday morning and early afternoon as well as
across Bristol Bay. Winter Weather Advisories have been issued for
the Kuskokwim Delta and Bristol Bay for trace amounts of freezing
rain. Precipitation will taper off from northwest to southeast
Wednesday afternoon.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

Unsettled but benign weather continues for the next 3 days across
the Bering/Aleutians. Winds will remain below gale force with no
high seas expected.

&&

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

Overall model agreement with deterministic and ensemble guidance
is fairly good in the long term with above average predictability
through Sunday before model solutions diverge. The notable weather
features include a high amplitude ridge over western Alaska and a
series of upper shortwaves and attendant surfaces lows attempting
to break down the ridge or ride over it's axis from a deep trough
over eastern Russia. The first shortwave and surface low will
transit the Bering Strait on Friday, with it's front likely
bringing an initial bout of rain followed quickly by snow to the
Kuskokwim Delta and River areas as the system occludes and much
colder air returns aloft. Other than some light precipitation and
gusty onshore winds, this system won't have much impact on the
AOR.

The primary focus for the long term will be a strong storm
developing along the southern periphery of the Russian trough and
moving quickly into the Western and Central Bering Saturday. This
looks like a likely high wind scenario for the Central and
Western Aleutians with widespread high seas and gale to storm
force winds across the Bering Saturday and Sunday. Models have
trended more towards yesterdays ECMWF track into the Gulf of
Anadyr, which would put the western coast of Alaska into
south-southeast flow. Lunar cycles are not supportive of a high
high-tide so that should help mitigate any coastal flood issues in
addition to the fetch of wind and waves no longer being as
favorable (south-southeast instead of southwest) for high water.
There remains a possibility for sea ice related issues but this
remains uncertain at this time.

As this strong low moves north into the High Arctic another will
be quick to follow. The main impact from this system will be a
sweeping front that will move across the Bering Sea Monday,
reaching the coast Monday morning. With the occlusion of the
previous low and additional cold air from this system, the
atmosphere will cool considerably, bringing the return of normal
winter weather to the region. The two subsequent storms will
likely be enough to break down the ridge or at least shift it far
enough to the east, to return precipitation to Southcentral.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning: 131.
		 Winter Weather Advisory: 155, 161.
MARINE...Gale Warning: 127.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AS
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ED
LONG TERM...CJ