Heavy Freezing Spray Warning 21, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
521 AM AKST Mon Jan 30 2023

.ANALYSIS AND UPPER LEVELS...

A longwave trough continues to be situated to the west of the
domain over East Asia, while ridging is located to the east over
the Northeast Pacific. Though the ridge still stretches up into
mainland Alaska this morning, heights are falling as it has begun
to slide back south and shift eastward. This has allowed a well-
defined front off a large low in the western Bering Sea to
approach the Southwest Alaska coastline. Rain is ongoing across
the Kuskokwim Delta and western Bristol Bay region as the front
begins to push inland. Temperatures are falling in association
with the front as well, with a colder airmass moving in behind
it. Mekoryuk has switched cleanly over to snow with the
temperature dropping to 32. Additionally, a triple point low is
developing along the front south of the Alaska Peninsula, where
temperatures are solidly in the upper 30s.

Over Southcentral, a large, disorganized area of enhanced
vorticity is contributing to widespread stratus, with some
localized fog impinging on north Anchorage. While the Kenai radar
has been seeing weak returns throughout the night, little if any
precipitation has been reported at the ground. Further north, in
the northern Susitna Valley, some upslope snow and rain continues
to be reported. Along the coast, rain and snow showers are moving
in around Prince William Sound. Low stratus is widespread across
the Gulf of Alaska.

Out west, another front defines the boundary of cold air and
colder air in the central Bering Sea within the larger swirling
mass of a former hurricane-force low. Within the colder air mass
over the western Bering, GLD has reported infrequent lightning
from convective cells. Cold advection in association with this air
mass is also allowing for a swath of southwesterly gales across
the western Aleutians.

&&

.MODEL DISCUSSION...

Models continue to handle the synoptic-scale pattern well and are
in good agreement. However, run to run differences continue to be
a significant source of uncertainty. Models now suggest that the
front tracking into Southwest Alaska today progresses eastward
slower than previous model consensus, with precipitation only
moving in appreciably over Southcentral by Tuesday night. There is
some divergence in solutions on Wednesday with a shortwave moving
north out of the Gulf of Alaska, which will impact whether
precipitation is reinforced, prolonging snow (as shown by GFS and
GEM) or the front continues to decay over Southcentral (indicated
by EC and NAM) going into Thursday.

&&

.AVIATION...

PANC...Fog and low stratus will have the potential to impact the
terminal through this morning. Low cig/vsby conditions should
lift to VFR by late morning. Slight precipitation chances hang on
through the morning but end by this afternoon, and are most likely
not going to impact ceilings or visibility. VFR conditions
continue into Tuesday, though a return of fog and low stratus
cannot be ruled out for Monday night into Tuesday morning. Winds
remain light through the forecast period.

&&

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

Southerly flow in the upper levels of the atmosphere will direct
shortwave troughs northward into Southcentral through Tuesday. The
first shortwave is moving into the northern Gulf this morning and
will push a front towards the coast, bringing rain and snow to
coastal locations. Farther inland, an upper level ridge will
weaken this shortwave, with very little energy and precipitation
pushing north of the coastal mountains. What moisture that does
push north today will be in the form of snow flurries or a very
light wintry mix of freezing rain and/or sleet. However, most
areas north of the coastal mountains will remain dry with cloudy
conditions. Several other weak shortwaves will move into
Southcentral tonight and Tuesday morning, with most of the
precipitation remaining along the coast and very light snow
flurries in the Susitna Valley tonight.

On Tuesday, a surface low will develop across the southeastern
Gulf. This will keep the bulk of the energy and moisture out over
the Gulf. Some weak shortwaves may still rotate north very slowly
into Southcentral, but the precipitation will be light and in the
form of snow as the airmass cools by Tuesday. On Wednesday, a
stronger shortwave trough will become slightly negatively tilted
as it approaches from the west and will bring a better chance of
snow across the area, especially from the Kenai Peninsula
northward into Anchorage and the Mat-Su valleys.

&&

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

A shortwave within a frontal system exists over Southwest Alaska
today, with a second front approaching the Southwest coast late
tonight. Flow will remain mostly southerly today, with
temperatures hovering at or above freezing for most areas this
afternoon. Thus, precipitation, while light, will be rain or a
rain/snow mix. Flow switches to westerly and colder air advected
in behind the initial front, causing temperatures to drop below
freezing tonight and persist through mid-week. Long-duration,
light, showery snow is expected across Southwest Alaska through
mid-week, with little accumulation likely for most areas. The
highest snow amounts will be in the Lower Kuskokwim Valley, near
Sleetmute, as they have less influence of warmer air to begin
with, but will still only see around 1 to 3 inches.

&&

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

There is a front sweeping across the Bering Sea towards the
Southwest coast today. A widespread area of small craft winds
extend into the central Bering, with an area of gale force winds
in the western Bering. High pressure ridging lifts from the
Pacific into the central Bering tomorrow, shifts eastward and
weakens. A developing low pressure system in the north Pacific
moves into the western Bering on Tuesday and slides northwards.
Widespread gale force winds are expected, with a band of
precipitation riding along the front. The low stalls in the
northern Bering on Wednesday and the front weakens rapidly as it
sits along the Southwest coast.

&&

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

Confidence is increasing that a north pacific low will continue to
deep and drive into the central Bering Wednesday into Thursday.
This system will be much weaker than the one that brought high
winds across the region this week. This low is expected to bring
only low end gales to the central aleutians as it moves towards
the coast. As cold temperatures have begun to return to much of
the state, most precipitation is expected to fall as snow as this
low drives inland into the weekend. Across southcentral, light
snow is anticipated most days, while a bigger driver in the form
of a weak trough will move across the Cook Inlet Region bringing
a a better chance late in the week. The pattern leading into the
weekend will remain rather progressive, though temperatures look
to remain near normal.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 175-178 411 413.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...CQ
SOUTHCENTRAL ALASKA...RC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KM
LONG TERM...AB