Gale Warning 370, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
450 AM 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 morning.
Mostly clear skies dominate from 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. A surface low and attendant upper-
level low are situated southwest of Yakutat this morning. These
features are producing scattered showers around the entrance of
Prince William Sound. A weaker upper-level wave is moving
southeast over the Kenai Peninsula and is ushering in some drier
air to its north and west.

As the aforementioned Kenai wave moves southeast, it will slow
and help draw the low in the Gulf back west, making landfall near
Kayak Island. The upper-level low will open into a wave, with a
vorticity lobe moving northwest over the Copper River Basin by
afternoon. Snow showers will become more likely through the day
for Cordova/Valdez, and over the western half of the Copper river
Basin, by Monday afternoon as the wave moves through the region.
Interior areas such as Anchorage and the Mat-Su Valleys will
likely be sheltered from the easterly moving waves, providing for
another nice day. With southwesterly low level flow developing
from Cook Inlet north to the Mat-Su Valleys, though, it is
possible that areas along the foothills of the Chugach and
Talkeetna Mountains see another round of shower activity much like
yesterday afternoon, with rimed snow and/or graupel.

By Tuesday morning, an upper-level Arctic Trough will dive into
Southwest Alaska, building a low pressure system that will cross
the Alaska Peninsula near the Barren Island. this low will be
broad due to the stout upper-level support and will envelop the
low to the northeast, amplifying the conditions across coastal
Southcentral. As such, 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 (below -40C at 500 mb)
coupled with diurnal heating at the surface will yield a very
unstable atmospheric profile developing near the low towards the
afternoon on Tuesday. This will help fuel vigorous bands of
convective 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.

-TM/CL

&&

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

Snow showers chances across the Alaska Peninsula and Eastern
Aleutians will continue into Tuesday morning. There may be brief
periods of reduced visibilities due to blowing snow during snow
showers. Cold air continues to pull southwards over over the
Bering Sea (primarily eastern portions) and Southwest Alaska.
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.

Conditions will be mostly cold and dry over Southwest until
Wednesday as a low pushes its front west to east across the
Bering Sea towards the Southwest Coast. Models have been trending
the associated front faster over the last few days and seem to be
coming into better agreement with the most recent model runs.
There is a chance for blowing snow or blizzard conditions across
the Kuskokwim Delta and Nunivak Island and the Western Capes of
Bristol Bay as the front moves in. There is a lesser chance for
impactful blowing snow across the Aleutians as warm air quickly
follows the front, however, there may be a quick shot of
snow/winds ahead of the warm air. Additionally, storm force winds
and widespread gales are expected in the western/central Bering
Sea along the front.

-KM

&&

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

Long term models are in relatively good agreement with the
amplification of a large upper low over the Bering on Thursday.
Several shortwaves digging around the low will bring it across
Southwest and into Southcentral into early Friday. A cold air mass
will remain in place across the Bering with gusty conditions
persisting along the Aleutian Chain and the potential for a winter
storm to push across the Kuskokwim Delta, the Lower Kuskokwim
Valley, and the Greater Bristol Bay regions during the same time
frame. This system will be the primary focus and concern during
the long term period as cold air over the Bering wraps around the
low into the Gulf and across Southcentral as well. With Anchorage
still in the running to have the snowiest winter on record,
Thursday could prove fruitful with a round of accumulating snow,
with widespread snow showers spreading across Southcentral. Due to
the nature of the expected airmass, lapse rates will be quite
steep, further supporting the notion of numerous snow showers
spilling over from Southwest Alaska into Southcentral. The
Canadian forecast model is the most bullish with the strength of
the trough moving into interior Alaska, with the GFS not far
behind. Still, it remains just far enough out in time that
forecast confidence will remain low until further run-to-run
consistency within model guidance is observed.

BL

&&

.AVIATION...

PANC...VFR conditions and light 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.

&&