High Wind Watch 9, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
450 AM AKDT Thu Apr 4 2024

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

A weakening frontal system is beginning to shift from the western
Gulf into the Kenai Peninsula this morning. This is following a
wave of moisture and lift that's bringing mostly snow up into the
Kenai Peninsula and Cook Inlet right about on schedule. Snow will
soon spread up into Anchorage, the Mat-Su and Prince William Sound
regions within the next few hours as the front continues to lift
northeast around an upper ridge beginning to shift towards
Southeast by this afternoon. Widespread accumulation of around an
inch is still expected through this afternoon from the Kenai
Peninsula north to Anchorage and the Mat Valley, with higher
amounts up to 5 inches across the northern Susitna Valley.

By late this afternoon, stubborn nuances with the forecast and
continued shifts in modeled depiction of a couple key features
begin to compound the overall forecast picture. With weak coastal
ridging building into the Prince William Sound ahead of the front
and broad low pressure focused over the Bering/Southwest, a gusty
southeasterly Turnagain Arm wind will develop and bend into
Anchorage by about midday today. This couped with daytime heating
in the afternoon could be enough to change falling snow over to
rain or a slushy rain/snow mix near sea level, particularly
between the western Kenai Peninsula and Mat Valley. Even so, there
will likely be a lull in precipitation intensity/coverage before
another window opens for briefly more intense snowfall for some
areas after sunset.

By this evening, a shortwave trough will move northeast from the
AKPen up into the Kenai Peninsula as a surface low also develops
out ahead of it and slowly deepens near Middleton Island. Around
the same time, weak cold advection will kick in as flow near the
surface shifts from southeasterly to westerly. This will help set
up a convergence zone along an axis from roughly Soldotna to
Palmer, and it's looking even more likely that this coupled with
lift ahead of the arriving shortwave will help a new band of snow
develop over the Mat Valley down into Anchorage tonight. Snowfall
accumulation will depend on how quickly temperatures at the
surface cool and where smaller scale banding sets up, but another
1 to locally 3 inches of wet snowfall accumulation is likely for
this corridor through early Friday morning.

From Friday onwards, things will become a bit less unsettled, but
still not very spring-like just yet. Snow will continue much of
the day on Friday near the Prince William Sound as the Gulf low
meanders slowly east. Snowfall farther east over Anchorage and
the Mat Valley will slowly become more focused over the western
slopes of the Kenai/Chugach Mountains as northwest flow continues
to wring out moisture as it upslopes into higher terrain. Upper
level troughing will become reinforced by additional waves digging
into the Gulf from Southwest between Friday and Saturday, but
overall most of Southcentral should still manage to slowly dry out
through the first half of the weekend.

&&

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

The longwave pattern features a trough axis bisecting the Bering
and a ridge over the Gulf Of Alaska. The trough axis will deepen
and the longwave pattern will amplify over the Pacific. An area
of low pressure in the northern Bering Sea will keep a persistent
fetch of southwesterly winds into Southwest Alaska. There is
potential for some minor coastal erosion with some
locations possibly seeing water levels reaching 1 to 2 feet above
highest astronomical tide. With shorefast ice along much of the
Kuskokwim Bay coastline, the most significant impact is likely to
be some water pooling on the icepack. Another North Pacific low
continue to move towards the western Aleutians, bringing gusty
winds and precipitation to the Western and Central Aleutians. The
surface low will move north of the chain on Friday and the front
will reach Bristol Bay early Saturday.

&&

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

The main feature on the Alaska weather map is an elongated trough
extending from the Arctic through the Mainland into the Gulf of
Alaska. Aside of some minor East-West swaying due to the
transitory shortwaves moving through the pattern, and the influx
of Arctic air over the Western Coastal areas, it remains in place
over Alaska through the forecast period. Most of the active
weather runs across Southern Alaska with upper level support.
There is another well developed system in the queue coming out of
the Russian Far East late Wednesday. Forecast confidence remains
good starting with the deterministic models and then sustaining
the forecast in the transition to the ensembles through midweek.

Gusty Westerly winds with areas of gale force gusts associated
with a well developed surface low spread across the Western and
Central Aleutians Sunday before moving out to sea over the North
Pacific Monday. Possible coastal flooding along the Western coasts
may include ice pushing onshore. Widespread precipitation, begins
as rain ahead of the low, but mixing with or changing over to
snow as the low passes to the East. As the low tracks over the
Alaska Peninsula, another round of gusty winds and local gales are
expected from Bristol Bay and the Pacific side of the AKPEN
around Kodiak Island until midweek as the low slide across the
Northern Gulf. Gusty winds are possible through Turnagain Arm
through Wednesday. Widespread rain or rain mixed with snow extends
along the Southcentral zones all the ways to the Canadian Border,
with mixed rain and snow or all snow further inland.

Kutz

&&

.AVIATION...

PANC...Conditions deteriorate by early morning as snow moves into
Anchorage. Visibilities and cloud ceilings will be mostly
IFR/MVFR through this evening. Warming this afternoon may allow
for a rain/snow mix. Turnagain arm winds pick up this afternoon
around 22Z and are expected to affect the terminal. Snow is
expected to be light.

&&