Gale Warning 16, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
451 AM AKST Mon Jan 15 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Wednesday night)...

Key Points:

* Dry conditions through the week.

* Colder and windy beginning Tuesday night.

* Strong winds likely for coastal communities mid to late week.
  This includes Seward, Whittier, and Valdez. Potential for
  damaging winds in Valdez (75 mph or greater) mid week.

A short-wave trough sandwiched between two ridges is sitting
overhead of Southcentral early this morning. It will exit eastward
this afternoon, with some light snow lingering this morning
across the eastern Copper River Basin. Weak cold air advection
with the trough and higher pressure off to the north and west will
lead to gap winds along the coast. As an upper ridge builds in
behind the short-wave, temperature inversions in place will
strengthen. Thus, fog which has formed over portions of Anchorage
and the western Kenai Peninsula will likely expand and linger
through Tuesday morning.

Another short-wave over the central Bering Sea this morning will
lift up and over top of the ridge over mainland Alaska. As it does
so, the center of the ridge over the Alaska Peninsula/western
Gulf will merge with a new ridge building over the western Bering,
leading to development of a much larger and stronger ridge
centered over the Bering Sea. This will force the aforementioned
short-wave to dig southward along the astern side of the ridge
Tuesday, bringing moderate to strong cold air advection to
Southcentral Tuesday afternoon through Wednesday. A strong
northerly jet will set up over Southcentral at all levels, while
pressure gradients rapidly tighten as a 1048 mb surface high sets
up over Interior Alaska. The result will be a "bora" (or
"katabatic") wind-storm, with widespread strong winds developing
through gaps in the mountain ranges. Most areas will see some
wind, but the strongest winds will be along the coastal gaps,
including Seward/Resurrection Bay and Valdez/Thompson Pass. Based
on the current location of the digging short-wave and strongest
cold air advection, the strongest winds will be in Valdez/Thompson
Pass and through the Copper River Delta. A tropopause fold on the
pole-ward side of the upper level jet streak will enhance winds
through this area, possibly leading to high (damaging winds).
While models are in good agreement right now, would like to see
another model cycle before issuing any High Wind Watches to ensure
consistency in the track of the digging short-wave. Any east-west
shift in the track would affect the area of strongest winds and
potential for high winds (75 mph or greater). The other threat
with the winds will be blowing snow and reduced visibilities,
particularly through Thompson Pass. Elsewhere, dry and colder
weather will settle in for the remainder of the week.

&&

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

A low in the northern Bering Sea tracking over Chukotka today is
aiding in drawing a stream of moisture from the North Pacific
across the central Aleutians/Bering Sea, accompanied by a swath of
gale force southerly winds. A warm front extends east from the
low across the Yukon Delta and into the Lower Kuskokwim Valley,
after having lifted through the Kuskokwim Delta overnight. This
will bring a dusting of snow to areas east of Aniak through the
morning hours, before the front lifts into the Interior. The cold
front across the central Bering Sea rapidly weakens today, with
winds diminishing below gale force by this evening and
precipitation largely coming to an end. The main exception,
however, will be along the northern portion of the domain, where
the front sweeps east across the Kuskokwim Delta tonight. There,
around half an inch of snow accumulation is likely for inland
locations, with a mix of rain and snow possible for Nunivak
Island and along the coast. Similar amounts of snow are expected
for portions of the Lower Kuskokwim Valley through Tuesday
morning until the front pushes into Southcentral Alaska.

For Tuesday, high pressure amplifies across the eastern Bering
and western Alaska, yielding primarily dry conditions which look
to continue through the work week. Precipitation will be confined
to the central and western Aleutians as weak shortwaves rotate
around the periphery of the high. Temperatures will begin the
week above climatological average, but will fall towards the end
of the week as cooler air filters in from the northeast.
Northeasterly winds increase across Southwest Alaska and the
eastern Bering Sea beginning Tuesday and continuing through much
of the week as a potent upper-level shortwave drops southward
into the Gulf of Alaska.

CQ

&&

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

An upper-level ridge will be situated over Southern Alaska and
the Bering Sea, suppressing active weather across our region
through next week into the next weekend. While the high pressure
is in place, a clear and cool pattern will prevail for most of
Southcentral and Southwest Alaska. There is the potential for some
low stratus and fog to develop in low lying areas given the
strength of the ridge that will be in place. With the high
pressure system centered over Southwest Alaska, models are keying
in on some low pressure system originating from the Gulf of Anadyr
and the Northern Pacific to move up the western-most Bering sea
and ride the northern edge of the ridge into Western Alaska. We
are monitoring the likelihood for pockets of energy swinging up
and over the northern side of the ridge to swing back down south
over Southcentral beginning Wednesday and continuing into the
weekend. Gusty winds and colder temperatures moving south will
likely be the impact felt for Southcentral and Southwest through
the latter half of the week into the weekend. Areas of outflow
winds develop along the Alaska Peninsula and Southcentral Coasts,
with gale force gap winds through the Barren Islands and Shelikof
Strait and along the Alaska Peninsula Coast into the Eastern
Aleutians developing for Thursday and diminishing Friday. By
Saturday afternoon, there is the potential for a new low to
approach coastal Southcentral from the Gulf of Alaska, however
uncertainty on this system remains high. Given cold temperatures
in the Copper River Basin, and gusty winds through the gaps
possible, a strong wind event blowing through portions of the
Matanuska Valley is possible by Friday. We will continue to
monitor this potential high pressure active pattern incoming to
Southern Alaska.

-CL

&&

.AVIATION...

PANC...Calm and variable winds will persist through the TAF
period. Conditions are favorable for fog development until winds
increase late tomorrow night and Wednesday morning. Fog could
move into the terminal at any time during the TAF period, dropping
vis and cigs as low as LIFR.

&&