High Wind Watch 3, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
433 PM AKST Tue Feb 7 2023

.ANALYSIS AND UPPER LEVELS...

A broad upper level trough stretches across the Bering and into
the Gulf with the Jet Stream running south of the Aleutians in a
zonal pattern towards the northwestern US. Several shortwaves and
weak surface lows are moving across the Bering with showers near
the Pribilofs. A stronger low is beginning to move near the
western Aleutians which will bring an increase in winds this
afternoon. Across the Gulf cold air aloft is supporting
convective showers with a surface low southeast of the Kenai
Peninsula with snow showers extending across the Peninsula.
Another shortwave is producing bands of snow showers across
eastern Prince William Sound with moderate to heavy snow showers
embedded in these bands. Farther inland relatively quiet weather
for Anchorage and the Mat-Su valleys with light snow across the
Copper River Basin. However, radar is showing snow showers
beginning to push northward towards Anchorage and the Susitna
valley.

&&

.MODEL DISCUSSION...

Model guidance is in good agreement with several shortwaves moving
across the Gulf and Southcentral. The main forecast challenge here
will be snow amounts across Anchorage and parts of the Matanuska
valley as low pressure may linger across Prince William Sound
which could bring higher snow totals to the area. Out west models
are in good agreement with a storm force low moving near the
Aleutian Chain Thursday and Friday.

&&

.AVIATION...
PANC...VFR conditions with light winds will persist through
midday. Snow returns after 00z with ceiling/visibility between
MVFR to IFR. Snow accumulations through tomorrow are expected to
be between 2 and 4 inches with the possibility of snow rates
nearing an inch an hour in the strongest bands of snow.

&&

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

At 500 mb there is a negatively tilt trough extending from Cook
Inlet to the Gulf of Alaska. Multiple shortwaves will continue
propagate across southcentral Alaska. These weak disturbances
aloft are producing pockets of snow that will continue into the
night. Bands of snow will move over Anchorage through Thompson
Pass/Valdez/Cordova. Looking at model data and satellite imagery,
the moisture advection component is relatively weak across the
region. The trough is then expected to linger over the area
before lifting north late Wednesday evening. Anticipate 1 to 4
inches of new snow at lower elevations, with locally higher
amounts possible in favored upslope areas, such as the coastal
mountains, Anchorage Hillside, areas from Palmer north and east.
Thursday will be dry but the temperatures will plunge. Expect low
temperatures ranging from single digits to subzero from Anchorage
to the Mat-Su Valleys.

&&

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

A cold but quiescent pattern will continue for the breadth of
Southwest over the next several days, until another pattern shift
begins towards the end of the week. While chances for accumulating
snow will remain rather low overall, a couple weak shortwaves will
rotate onshore from the Bering around an upper trough anchored
near the Y-K delta through Thursday morning. Snow showers will be
possible as these weak waves move onshore, mainly between Bristol
Bay and parts of the Kuskokwim Delta. Otherwise, little activity
is expected across the majority of Southwest through Thursday
night, with bitterly cold lows each night dipping well below 0
Fahrenheit, especially across the Lower Kuskokwim Valley and
Kuskokwim Delta.

By Friday morning, the initial effects will begin to be felt from
a front extending out ahead of a storm force low following along
the Aleutian Chain. Gusty offshore, easterly winds will pick up
along with increasing cloud cover throughout the day on Friday as
the front moves up the Alaska Peninsula towards Bristol Bay.
Chances for steady, light snowfall will increase for areas
favoring upslope enhancement with strong east to southeast flow
ahead of the boundary, namely over and immediately east of the
Kuskokwim Mountains. The best chance for perhaps an inch or two
of new snowfall through Friday night will be near the Dillingham
and Aleknagik area, with areas of blowing snow also possible in
this vicinity as easterly winds ahead of the approaching low
continue through Friday evening. Warm advection with the
increasing southeasterly flow should also push much of the region
out of the deep freeze, with highs moving back towards the 10s
and 20s on Friday afternoon.

&&

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

A myriad of small, weak lows periodically spinning up and
dissipating will continue to affect portions of the Aleutian Chain
and Pribilofs through Wednesday night as a broad, disorganized
trough continues to drift across the Bering Sea. Predominant winds
will generally stay in small craft range or lower through
Wednesday, however stronger winds will be possible for very
localized areas near the more potent mesoscale lows spinning up
along dynamically unstable boundaries (including those currently
visible on satellite). Aside from these areas of gustier winds and
a few snow showers, relatively calm conditions will persist until
the arrival of a much stronger system starting on Thursday.

By early Thursday, a strong North Pacific low and its attendant
front will approach central portions of the Aleutian Chain from
the southwest. Easterly winds will ramp up quickly as the gradient
between the deep low pressure and high pressure remaining in place
over the central Bering, with sustained winds peaking in storm
force range along the central Aleutians as the front moves past on
Thursday. Temperatures will initially be cold enough for wet snow
with a shield of precipitation moving out ahead of the low and
frontal axis, but a changeover to mostly rain is likely for most
spots a few hours after the onset of precipitation on Thursday.
Winds will mostly drop off along eastern portions of the Aleutians
between Thursday night and Friday as the low begins to follow
right along the Chain, but stiff northeasterlies will persist well
into gale force range on both the Pacific and Bering side as the
low slowly drifts up into the southern Alaska Peninsula through
Friday. Strong north to northeast winds will similarly persist
across the Pribilofs and on the back side of the low towards the
western Aleutians, with rain gradually transitioning back to snow
as colder air wraps back in from the north behind the low passage.
Extensive areas of freezing spray will develop close to the ice
edge as strong cold advection and gusty northerly winds increase
between Thursday night and Friday.

&&

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

A progressive, amplified pattern is expected to keep active
weather ongoing across southern mainland Alaska this weekend into
next week. The weekend looks to begin with low pressure in the
Gulf of Alaska, with a front initially bringing heavy
precipitation decaying and turning showery. Another low enters
the Gulf on Saturday, reinforcing low pressure and bringing
another round of heavier precipitation along the coast by
Saturday night. The track of the low will serve to keep much of
the precipitation from moving inland, and with little warm air
making its way into the mainland. However, models indicate a weak
front may bring light snow on the back side of the low over
Southwest Alaska for Sunday, moving into Southcentral by Monday,
but the light nature of the precipitation is expected to limit
snow amounts to just a few inches. Cold air, as cold as -24C at
850 mb, moves in over the Bering Sea and Southwest Alaska on
Sunday, cooling temperatures at the surface and helping to drive
strong gap winds on the south side of the Alaska Peninsula and
along the western Gulf. These winds are likely to gust to storm
force, and in localized areas storm force winds may be sustained.
Gap winds diminish going into Monday as the low pressure in the
Gulf weakens. Shower activity decreases along the north Gulf coast
as a result, and the decaying front leaves much of the southern
mainland dry by Monday night.

At the same time, a strong storm force, or potentially hurricane
force, low in the North Pacific approaches the Aleutian Islands.
Current model consensus suggests that the low tracks several
hundred miles south of the islands, but its front pushes across
the central and eastern Aleutians on Monday. This may bring
easterly winds as strong as storm force along with snow, as a
colder air mass remains in place over the Bering. Snow moves up
along the Alaska Peninsula into Bristol Bay and over Kodiak Island
on Tuesday. While the low dips back into the North Pacific, a
southerly oriented warm conveyer belt brings a continued push of
moisture to fuel precipitation. Transient high pressure enters
the Bering Sea on Tuesday within a very amplified pattern, which
will bring drier conditions. Then, a strong front off a deep low
near the Kamchatka Peninsula looks to bring rain to the western
Aleutians on a southerly push of warmer air late on Tuesday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning: 130, 176, 411
 		 Heavy Freezing: 180, 185
FIRE WEATHER...NONE.

&&

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