Gale Warning 286, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
531 AM AKDT Sun Apr 9 2023

.ANALYSIS AND UPPER LEVELS...

At upper levels, a large low remains anchored near Point Hope
while it extends a shortwave southward across the center of the
entire Mainland. The associated trough axis is located over Kodiak
Island. Out west, a ridge of high pressure continues to build
eastward across the Bering and Aleutians.

At the surface, a low complex sits over the eastern Gulf and is
extending an inverted trough northward into the Southcentral
coast. As of early this morning, the core of strongest snow is
located over the eastern Prince William Sound. To the west, very
cold temperatures and generally clearer skies are the name of the
game for Southwest Alaska as high pressure lingers near the
surface and a polar airmass moves south behind the digging
shortwave. Strong, cold northwesterly winds continue across the
Barren Islands, Alaska Peninsula, and eastern Aleutians. The gusty
winds are resuspending ash from the Katmai volcano, as seen on
satellite. Further west, a Kamchatka low extends a front across
the central Bering and eastern Aleutians. Elevated winds and rain
accompany the low as it pushes east.

&&

.MODEL DISCUSSION...

With respect to the inverted trough reaching eastern Prince
William Sound this morning, the GFS solution seems to have
initialized the best. The GFS continues to be the quickest
solution overall with this system and the NAM is still the
slowest. Models continue to struggle with the track of the
associated low as it moves from the eastern Gulf toward
Southcentral. The current 06z runs already show low placement
discrepancies by around 21z today. For instance, by this time the
GFS brings the low center over Middleton Island while the other
models keep it roughly 120 nm to the southeast. As the low tracks
closer to the Southcentral coast by tonight, the GFS is the
westernmost solution brining the low to the eastern Kenai
Peninsula coast, the NAM and the Canadian are the more eastern
solutions bringing the low near eastern Prince William Sound, and
the EC is the in-between solution.

&&

.AVIATION...
PANC...VFR conditions are expected to drop down to as low as IFR
later this morning with the arrival of some heavier snowfall. The
snow is anticipated to continue into the afternoon before
tapering off by this evening. Ceilings and visibility will
gradually increase with the lightening of the snow. Gusty
northerly winds should start to diminish by this afternoon.

&&

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

A complex storm remains on track to bring more spring snowfall to
Southcentral through early Monday morning. Today's system is
driven by a deep upper low and unseasonably cold airmass centered
over northwest Alaska, and a series of shortwaves moving north-
northwest along the Panhandle and into the Gulf Coast. The core of
the snow as of 4am is over the eastern Prince William Sound to
the north side of an elongated surface low. This should be fairly
short-lived for this area as the front pivots quickly into the
Western Sound, overspreading into the Anchorage area and Mat-Su
Valleys this morning. Northwesterly flow in the low-to mid-levels
of the atmosphere, driven by cold air advection driving through
the gaps of the Alaska Range as well as forcing from the low in
the Gulf, will provide upslope enhancement to the western facing
slopes of the Chugach Front Range. As such, snowfall totals will
be higher the closer you get to the mountains.

The wind forecast over the marine areas is perhaps the most
complex aspect to this forecast due to the interaction of the
surface low with the abundance of arctic air streaming from
western Alaska through the gaps and passes of Southcentral into
the Gulf. Some forecast guidance indicates a solution that places
the low in the Prince William Sound by late tonight; however, the
upper level low and area of high baroclinicity is expected to be
south of the Kenai Peninsula, so the favored low location should
be in this area. As such, precipitation should come to an end over
the population centers around sundown tonight as the main energy
from the system drifts south. Should the low track more into the
Sound, snow will likely linger longer into Monday.

Influence from this system will wane quickly on Monday, leaving
behind some coastal snow showers. There is a possibility that snow
will linger for the Anchorage area and Mat-Su Valleys through
Tuesday morning due to deformation aloft, though accumulation will
be minimal. By late Tuesday afternoon, yet another system will
move in from the southwest, bringing another chance for snow to
the region.

&&

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

The main weather feature continues to be a deep upper-level low
that will remain anchored by a cold, Arctic air mass over
northwest Alaska through Tuesday. This feature, in combination
with a weak surface high pressure over the eastern Bering, will
bring colder air to Southwest Alaska with northwesterly flow
through Monday. A weak shortwave will bring a chance of snow
to the Kuskokwim Delta through the evening today. Another cold and
mostly clear night is expected tonight as the aforementioned shortwave
weakens and precipitation chances decrease. Temperatures continue
to moderate for Monday as an incoming ridge starts to push the
cold air mass out of the forecast area. By Monday evening, a
front extending off a Kamchatka low pushes into the Southwest
coast, bringing roughly 2 to 4 inches of snow Monday night into
Tuesday. Highest amounts seem to be confined to the Kuskokwim
Delta region with lesser amounts further inland. Blowing snow
will be possible with this front, but there is uncertainty in the
extent and severity of the threat. Be sure to check back with the
forecast as the finer detail's of this feature become more
resolved.

&&

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

A Kamchatka low will gradually replace northwesterly flow and
cold air with southwesterly flow and warmer air as it pushes a
series of fronts into the Bering. Several weak meso-scale lows
will track through the central and eastern Bering throughout
today, promoting periods of light snow showers for the Pribilof
Islands, eastern Aleutians, and the Alaska Peninsula for the
remainder of the weekend. A warm front will reach the central and
eastern Bering by Monday, bringing a band of light snow and rain
to the islands. However, a stronger front will traverse into the
western Bering/Aleutians tonight. The aforementioned front will
have gale force winds accompany it along with a swath of precipitation
as it tracks towards the Southwest for Monday night. The
southerly winds with this front will aide in bringing warmer air
to the region and will result in the main precipitation type with
this front to be all rain for the Aleutian Chain and Pribilof
Islands. By Wednesday, a more zonal/progressive pattern will move
into the Bering with widespread snow showers and small craft
westerly winds.

&&

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

Overall synoptic flow appears to be in relatively good agreement
for the long term, but consensus begins to breakdown toward the
weekend. Zonal flow appears favorable across southern Alaska as a
polar low continues to flattened a ridge near the mainland. A
western Bering low will propagate shortwaves along this flow,
helping to break down any amplification of the upper level
pattern. This paves the way for embedded troughs to travel a more
southerly track across the Gulf of Alaska. While the prevailing
pattern appears to be unsettled overall, the bulk of the moisture
plumes is nudging more toward Southeast Alaska.

The Bering low and the polar low appear to have some interaction
for Thursday that will help to destabilize the cooler airmass over
the western and northern portions of the state as the bulk of the
Bering low energy attempts to shift into the Gulf of Alaska.
There is a high probability for the odds to favor colder than
normal temperatures across southern Alaska. Northerly and offshore
flow is possible as the low nudges southward and the cold airmass
points toward Southwest. Winds with cold air advection for the
last half of the week could lead to accelerated outflow winds for
the Alaska Peninsula and as far west as the Pribilofs and the
eastern Aleutians. The exact location and timing of the polar low
movement, along with interacting troughs from the west, increases
forecast uncertainty.

&&

SYNOPSIS AND MODEL DISCUSSION...AF
SOUTHCENTRAL ALASKA...CJ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...NS
LONG TERM...VR