Gale Warning 233, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
440 PM AKST Wed Mar 8 2023

.ANALYSIS AND UPPER LEVELS...

In the upper levels the anomalous ridge is reorienting across the
eastern half of Alaska with a shortwave moving across western
Alaska in the Fairbanks area. This shortwave is beginning to
reorient the ridge and shift it westward over the eastern Bering
over the next 24 hours. Otherwise, light snow is occurring across
the Kuskokwim Delta and valley areas associated with the
shortwave, with high level clouds spilling over the ridge into
Southcentral. A low pressure system south of the eastern Aleutians
is pulling moisture northward across the eastern Aleutians and
AKPen with areas of light rain, low ceilings and some fog as warm
air is pumped into the area. Across Southcentral low level clouds
are spreading across the northern Gulf and Prince William Sound.

&&

.MODEL DISCUSSION...

Model guidance is in good agreement with a pair of shortwaves
moving across Southcentral Thursday and Friday bringing colder air
and strong gap winds. The main forecast challenge will be the
possibility of high winds across Valdez and Thompson Pass Thursday
evening through Friday. Also, strong winds across the Matanuska
Valley with gusty winds up to 50 knots possibly extending along
the Glenn Highway from the Hay Flats to Chugiak and towards the
JBER area as well as western Anchorage, with 35 to 40 knot gusts
possible. These winds may also resuspend some of the snow reducing
visibilities.

&&

.AVIATION...

PANC...VFR conditions and light winds will persist. There may be
a brief lowering of the ceilings to 5,000 to 7,000 feet this
evening and tonight but should remain VFR.

&&

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

Warm and quiet conditions today give way to colder temperatures
and stronger winds by Thursday night. The ridge that has persisted
over Southcentral Alaska for the past few days will weaken tonight
as a shortwave moves over top of it. Little to no precipitation
continues to be expected for much of Southcentral; most locations
will see increased cloud cover tonight, but light snow will be
limited to higher elevations in the Copper River Basin.

A surface low develops in the Eastern Gulf Thursday as the
shortwave exits into the Eastern Gulf. The north-south pressure
gradient across the state tightens as a 1040 mb Bering ridge
tilts into Northern Alaska. With another upper level shortwave
descending south across the Eastern Chugach range on Friday and
cold air filtering into Eastern Alaska, the stage is set for gusty
outflow winds.

A High Wind Watch is in effect for Valdez and Thompson Pass from
late Thursday night into Friday, with max gusts of 80 mph
possible as cold air channels out of the Copper River Basin.
Further east, a Special Weather Statement is in effect for
Matanuska Valley and Anchorage as cold outflow winds (weaker than
those expected for Valdez and Thompson Pass) exit the Copper River
Basin and move south along Knik Arm and Cook Inlet. Though melting
and compaction from our recent warm weather has likely shored up
the snowpack, there remains a potential for blowing snow with
these stronger winds. Confidence is lower for max wind gusts
through Matanuska Valley and Anchorage, so stay tuned as we
continue to update the forecast.

&&

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

A shortwave trough that has since tracked over the Kuskokwim Delta
earlier this morning is now making its way across the Kuskokwim
Valley bringing light snow showers to the area. Once the
aforementioned shortwave tracks further east, an upper-level ridge
will set up and bring widespread dry conditions back to Southwest.
This will lead to the development of offshore flow and will bring
cooler temperatures and drier conditions back to the region
through the weekend.

&&

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

An upper-level ridge of high pressure, originally located over
the Gulf of Alaska, is swinging its way over to the Bering. This
high pressure will expand across the Bering through the end of the
week with continued benign conditions forecasted. Any moisture
trapped beneath the aforementioned ridge will likely introduce
persistent fog and low-level stratus for the Bering, Aleutians,
and Pribilofs. A warm front weakening to an inverted trough is
forecast to continue tracking across the Chain east to west and
reach Atka and Adak by Thursday afternoon. A weak trough over the
far western Aleutians may produce some widely scattered showers
for Attu and Shemya through tomorrow morning. Leading into the
weekend, the ridge of high pressure will dominant the region and
lead to drier conditions and warmer temperatures across the
Chain/Bering.

&&

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

The long term begins Saturday night with an upper-level ridge
anchored over the eastern Aleutians and extending northeast across
the interior of the state. This feature is bisecting two upper-
level shortwave troughs. The first looks to be exiting the Gulf of
Alaska to the south, with the resultant northerly flow between it
and the ridge over interior Alaska keeping clear but cols across
much of the Southern Mainland. The orientation of these feature
will also likely maintain the gusty gap winds along the
Southcentral coast; however, these winds should be well below
their expected peak from previous days.

The ridge then quickly retreats to south of the eastern Aleutians
for Sunday as that second shortwave moves south and east from the
Chukchi Sea to a position somewhere over the southern half of the
state by Monday morning. While the position and strength vary
between models, the result is generally the same: a resurgence of
arctic air and temperatures falling well below normal, especially
across Southcentral Alaska. This pattern looks to further amplify
by Tuesday as yet another shortwave dives from eastern Russia
toward southern Alaska as an upper-level ridge builds between the
western Aleutians and the Kamchatka Peninsula. Areas of light
snow, mainly at higher elevations, is possible with this systems
as it drives a surface cold front from west to east across the
state. The bigger story, though, will be a reinforcement of colder
air with 850 mb (~4500 ft) temperatures potentially falling to
-20 degrees Celsius or colder across the region. This would likely
correspond to daytime highs across the region struggling to get
out of the teens for most locations, especially across interior
Southcentral and Southwest Alaska by Wednesday, temperatures more
climatologically representative of mid-January than mid-March.
Along with the cold temperatures, this pattern will likely keep
the gusty gap winds along the coast persisting through mid-week
next week.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Watch 131.
MARINE...Gale Northern Gulf of AK
 Heavy Freezing Spray Bristol Bay, Kuskokwim Delta
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHCENTRAL ALASKA...KC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...NS
LONG TERM...TM