Gale Warning 372, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
451 PM AKDT Mon Apr 8 2024

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

Conditions are generally quiet across Southcentral this
afternoon. Mostly clear skies are present across much of Cook
Inlet north into the Susitna Valley along with scattered cloud
cover across the Copper River Basin associated with the remnants
of a weak upper-level wave moving into the Yukon. However, areas
along the foothills of the Chugach and Talkeetna Mountains are
seeing another round of shower activity capable of producing rimed
snow and/or graupel. A surface low and attendant upper-level low
are moving inland just east of Kayak Island this afternoon. These
features are producing scattered showers just east of Prince
William Sound, although they are slightly further north and east
than previously modeled. As such, while snow showers will become
more likely through early tonight for Cordova/Valdez, the heaviest
looks to remain north and east over portions of the Copper River
Basin as the wave moves through the region.

By Tuesday morning, an upper-level Arctic trough will dive into
Southwest Alaska, with a weak broad low developing near the Barren
Islands. This low will envelop the low to the northeast,
amplifying the conditions across coastal Southcentral. A return to
widespread snowfall will come to the coast from Seward to
Cordova. By this time, cold air will begin to wrap all the way
around the low, ushering a colder air mass into the Kenai
Peninsula up into the Mat-Su from the southeast. Very cold
temperatures aloft (near -40C at 500 mb) coupled with diurnal
heating at the surface will yield a very unstable atmospheric
profile near the low during the afternoon on Tuesday. This will
help fuel vigorous bands of convective high ratio snow showers
streaming into the coast, especially along the eastern Kenai
Peninsula and across the Prince William Sound. Some of this
activity will likely spill over the mountains into interior
Southcentral from Tuesday afternoon into Tuesday night,
potentially affecting parts of the Mat Valley, Anchorage and the
eastern parts of the Kenai Peninsula at times. Snowfall
accumulation could vary wildly depending on exactly where bands of
showers train over the same areas, with the best chance for
several inches of accumulation on Tuesday focused near Seward,
Whittier, Valdez and Cordova.

-ME/TM

&&

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

An Arctic trough has plunged south into Southwest Alaska, and
established a pressure gradient conducive for cold and gusty
northerly winds in the eastern Bering Sea and across the eastern
Aleutian Chain. Strong gap winds south of the Alaska Peninsula
will reach as high to 65 knots (75 mph) in some areas. Extreme
freezing spray along the ice edge will continue through tonight
for most areas, and through Tuesday in Bristol Bay. Some areas of
heavy freezing spray could be possible through gaps south of the
AKPen. These cold and gusty conditions are expected to persist
until Wednesday morning before shutting off.

This pattern shift will be driven by a couplet of lows in the
northern Bering Sea pushing a series of fronts beginning with a
weak front entering the Bering and moving over the Pribilofs by
Tuesday morning. This initial front is not expected to be very
potent, but should bring about an inch of snow to the Pribs by
Tuesday afternoon before being absorbed by a significantly
stronger front rapidly approaching from behind it. This stronger
system will bring storm force winds initially across the western
Aleutians, along with warmer temperatures, and moderate to heavy
rainfall starting Tuesday evening. This system will push quickly
to the northeast, spreading strong winds and rainfall across the
Aleutians, reaching Adak, the Pribilofs, and Nunivak Island by
Wednesday morning. The front will continue to spread rain and
rain/snow mix across the Aleutians through midweek.

As the front moves over Nunivak Island and enters the Kuskokwim
Delta Wednesday morning, temperatures are expected to be cold
enough to allow for widespread moderate to heavy snowfall. The
system will also be bringing strong and gusty winds up to 50 mph,
and this is expected to produce blowing snow. Blowing snow may
reduce visibilities down to one-quarter mile or less at times. The
worst conditions are expected to be along the Kuskokwim Delta
coastline, where snow accumulations may reach up to 8 inches of
new snowfall. As such, a Winter Storm Watch has been issued for
the Kuskokwim Delta from Wednesday morning through Thursday
morning. The front is expected to bring similar conditions to the
Western Capes of Bristol Bay, however being further south, the
presence of warmer air may keep the precipitation wetter, and
harder to loft with gusty winds. However, we will continue to
monitor the latest model trends and will update this region as
needed.

-CL

&&

.LONG TERM FORECAST (Days 4 through 7: Friday through Monday)...

The long term forecast begins on Friday with a shortwave ridge
exiting the eastern Gulf of Alaska and a large upper-level trough
over western Alaska. As a result, low pressure at the surface
spreads across Southwest Alaska, and a surface low briefly
develops over the Gulf early on Friday. A cold air mass will
remain in place over western Alaska while also spilling into the
Gulf. As the trough digs to the east, gusty winds and
precipitation taper off across most of Southwest by Saturday
morning as northwesterly gap winds increase along the Alaska
Peninsula. The system will maintain precipitation across
Southcentral through Saturday. The upper low and its attendant
surface low will exit into Southeast Alaska on Sunday. Model
agreement really begins to diverge on Monday with an Arctic upper-
level low. A potent shortwave is advertised to round the base of
the low and enter into western Alaska, however, the exact
placement of the wave (and, thus, the attendant surface low) has
yet to be ironed out. The deterministic GFS and Canadian NH runs
are the most similar to each other, while the EC is the slowest in
bringing the shortwave to western Alaska.

AF

&&

.AVIATION...

PANC...VFR conditions and light winds will persist. Isolated
showers may develop along the Anchorage Hillside and foothills of
the Chugach Mountains Tuesday afternoon and evening. However, any
shower activity should stay along the higher terrain and away from
the terminal.

&&

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
258 AM AKDT Tue Apr 9 2024

AKZ103-126-100200-
East Turnagain Arm-Western Prince William Sound-
Including the cities of Girdwood, Portage, Whittier, Seward,
and Moose Pass
258 AM AKDT Tue Apr 9 2024

...BANDS OF MODERATE TO HEAVY SNOW SHOWERS ACROSS EASTERN KENAI
PENINSULA AND EASTERN TURNAGAIN ARM THROUGH TUESDAY EVENING...

Bands of moderate to heavy snow showers will move across Eastern
Kenai Peninsula and Eastern Turnagain Arm through Tuesday evening.
The first of these bands will move through the area early to mid
Tuesday morning with the second late Tuesday morning through mid
Tuesday afternoon. Snowfall rates may approach 1 to 2 inches per
hour in heavier snow showers, reducing visibility to as low as
one quarter mile at times. Motorists are urged to slow down and
use caution when driving through heavy snow showers.

The highest snowfall accumulations are expected along Portage
Glacier Road, where 5 to 10 inches of snow could fall. Elsewhere
along the Seward Highway, 2 to 6 inches of snow, with locally
higher amounts, are possible. Any snow accumulations on area
roads this morning may turn slushy or wet by afternoon as
temperatures warm into the mid 30s.