Gale Warning 375, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
522 AM AKDT Wed Apr 10 2024

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

The upper level Gulf low that has plagued the forecast with
numerous rounds of convective snow banding/showers over the past
day or so is finally beginning to retreat south and away from
Southcentral this morning. One final meso-low feature will rotate
east and south past Middleton Island today, perhaps prolonging
snowfall already ongoing near Cordova for a bit longer into this
afternoon. Elsewhere over the interior, the atmosphere has finally
begun to stabilize as mid to upper level temperatures warm north
of the retreating upper level low, with some nuisance low stratus
spreading in behind the overnight snow showers across the Mat
Valley and Anchorage area. Any lingering showers along the coast
should diminish by this evening as a transient shortwave ridge
moves in ahead of the next more important feature moving into the
picture late this week.

By Thursday morning, the upper ridge will begin to flatten out as
a strong frontal system moving over Southwest begins to impinge
onto the western Gulf. During the day on Thursday, strong
southerly flow will rapidly pick up in the low levels while a belt
of southwesterly flow shifts southeast into Southcentral closer
to the jet level aloft. A strong south to north pressure gradient
will set up along the coast out ahead of the front, leading to
fierce south to southeast gap winds picking up across multiple
areas. Gusts near the peak of the wind event could reach 50 mph
across the Copper River Basin near Gulkana, the Mat Valley near
Palmer, and along the Turnagain Arm. The strong south to north
gradient will easily bend the Turnagain Arm jet into Anchorage,
where widespread wind gusts a high as 40 to 50 mph will again be
possible on Thursday afternoon and evening.

The other aspect of this system will be largely upslope driven
mountain and higher elevation snow. Heavier snowfall rates most
notably concentrated along the eastern Kenai peninsula, Hatcher
Pass, and the northern Susitna Valley near Broad Pass, where a
Winter Weather Advisory is now in effect for total snowfall
accumulation up to 14 inches. The air mass moving in ahead of the
front does not look particularly warm, and several inches of snow
accumulation down to sea level near Seward will also be possible
through Thursday evening if precipitation can manage to stay all
snow. With only a shallow layer of south to southeast flow in
place and mostly southwesterlies aloft, even Anchorage could see a
period of snow or rain/snow mix on Thursday before the front
moves through.

By early Friday morning, the front will push out to Prince William
Sound as it begins to weaken, with a new weak low potentially
developing along it over the far northern Gulf. This should
finally allow the strong onshore gradient to weaken, and strong
southerly winds should drop off considerably by late Friday
morning. Meanwhile, a broad upper level trough with multiple
embedded smaller shortwaves will shift east over Mat-Su and Cook
Inlet region through Friday evening. This will keep lift and
generally southwesterly flow in place for much of the day,
supporting several more inches of snowfall accumulation across
the Anchorage Hillside and northeastern portions of the Mat-Su, as
well as near Valdez and Cordova.

-AS

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA, BERING SEA, AND ALEUTIAN
ISLANDS (Days 1 through 3)...

Satellite imagery this morning shows a vertically stacked low
filling in over Kodiak Island this morning. Low stratus and
scattered areas of snow showers persist from Iliamna to Bristol
Bay; however both the extent of low cloud cover and snow will
continue to wane through the morning hours. Farther west, the
main weather features are two distinct surface lows, one over the
Bering Strait and the second off the east coast of the Kamchatka
Peninsula.

The Bering Strait low is extending a front south across the
eastern Bering. This front will quickly occlude today as it moves
inland, weakens and slows in its forward progression. As this
first system weakens, the second low and its frontal system will
move across the Bering, reaching the eastern Bering by late
afternoon. Warmer air will accompany this front, with temperatures
warming into the mid to upper 30 across the Bering and into the
40s along the Aleutian Chain. COlder air ahead of both fronts will
result in snow across southwest Alaska, with copious moisture
advection with the second front. Southerly winds will also
increase with the approach of each front, with blowing snow first
for The Kuskokwim Delta coast this morning, spreading east
through the day. Enough warm air may reach the coast for a brief
transition to mixed precipitation tonight before this second front
occludes as colder air begins to work in and any mixed
precipitation changes back to snow.

This second front reaches the Alaska Range by late Thursday. A
trailing shortwave and surface trough will introduce a colder
airmass across the Bering, eventually moving into Southwest
Alaska Thursday night and the Alaska Peninsula for Friday. A
continuous moisture feed and instability with the trough will
allow for gusty southwesterly winds and snow showers to persist
through Friday afternoon. Snow showers will also develop for the
western Aleutians and Pribilofs by late Thursday along with storm-
force wind gusts across the Bering.

Snowfall amounts of 7 to 10 inches are possible for the Kuskokwim
Delta, 4 to 8 inches for the Kuskokwim Valley, and 9 to 13 inches
for the Western Capes of Bristol Bay with through Thursday. Wind
gusts of 35 to 50 mph along the coast could result is blowing
snow reducing visibility to as low as one half to one quarter
mile. Given the expected conditions, multiple Winter Weather
Advisories and Blizzard Warnings are in effect across Southwest
Alaska.

&&

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

By Saturday morning, a deep upper-level trough will be moving
east over Southcentral Alaska, with weak ridging building over
the central Bering. This would lead to a widespread showery
pattern over the northern Gulf of Alaska and relatively calm
conditions over the Bering and Aleutians early this weekend. The
upper low and its attendant surface low will exit into Southeast
Alaska on Sunday. This will lead into a fairly benign pattern
across much of southern Alaska as the ridge once over the Bering,
shifts over our region, allowing for clearer skies and weak winds
across the area. By Tuesday morning, multiple low pressure systems
will approach the Chain from the northern Pacific. Model
agreement regarding the breakdown of a ridge is usually poor, and
remains so in this case, but either way, a significant shift in
pattern does not seem evident. A prolonged break in active weather
seems most likely currently for the latter portion of this
weekend into early next week.

-CL

&&

.AVIATION...

PANC...Areas of light snow showers early this morning are in the
process of quickly diminishing, and predominantly VFR conditions
are expected to return for most of the TAF period. Some low
stratus and patchy fog developing in the wake of snow shower
activity overnight could lead to periods of IFR conditions or
lower for the first few hours of the morning, but this should
scatter out by midday at the latest. Late tonight into Thursday
morning, a gusty south to southeast wind from the Turnagain Arm
will resume ahead of a front moving in from the west.

-AS

&&