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000
FXAK68 PAFC 221319
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
519 AM AKDT Mon Apr 22 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Wednesday night)...

In the upper levels, a ridge extends from western Canada northwestward
to the norther Alaska Mainland. A vertically stacked low positioned
just south of the Gulf of Alaska, with winds and precipitation
overspreading the Gulf offshore marine areas. A trough extends
northwestward from this low to a second weaker upper level low
over interior Bristol Bay. A short-wave trough which tracked
across Southcentral yesterday is pulling this low northward toward
the Kuskokwim Delta. Upstream, a short-wave ridge is building
ahead of a very large and deep low over the western Aleutians.
Weather for Kodiak Island, the Gulf waters, and Southcentral is
fairly quiet, with a hodgepodge of clouds and clear areas across
the region. Persistent low level instability (due to cool air
above the surface up to around 700mb) is leading to showers
primarily along the Gulf coast.

As surface temperatures warm today, expect isolated to scattered
showers. There is little in the way of upper level forcing, so the
coast and upslope areas will be favored. As the Aleutian low and
associated trough and basal jet progress eastward tonight, the
upper low over interior Southwest Alaska and trough trailing to
the southeast will be pushed back eastward to Southcentral. Models
have really struggled with the track of this feature, but the
latest solutions are converging around a common track - even if
there still is some spread in the exact track. Generally expect
the low and trough to track into Cook Inlet and the western Gulf
tonight, then weaken as increasing anticyclonic flow around the
upstream ridge pushes it southeastward across the Kenai Peninsula
on Tuesday. The NAM is a clear outlier with a more northern track.
With better model agreement, have tried to better dial in the
precipitation forecast tonight through Tuesday, with the focus of
steady precipitation over the southern to eastern Kenai Peninsula,
as moisture is pulled northward from the Gulf system ahead of the
upper low and trough. Secondarily, low level flow off the Gulf
will advect some of the precipitation to Kodiak as well. In any
case, precipitation will be light. The remainder of Southcentral
will continue a chance of showers, though with weak forcing they
will remain isolated to scattered in coverage (at most).

Conditions will dry out Tuesday, with some breaks of sun developing
by afternoon for most areas. The ridge ahead of the Aleutian low
will strengthen over northern Alaska Wednesday, while the remnants
of the trough sit over Southcentral. Expect mostly dry conditions
across Southcentral with increasing sunshine and slightly warmer
temperatures. Meanwhile, a weakening occluded front from the
Aleutian low will approach Kodiak Island Wednesday through
Wednesday night, leading to the return of steady light rain.

-SEB

&&


.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days
1 through 3)...

Weak ridging just offshore will promote areas of patchy fog this
morning along portions of the Southwest Coast. Further inland,
shortwaves passing through will provide opportunities for showery
activity to continue through this afternoon. The low situated in
the western Bering Sea continues to strengthen today. Along the
associated front, anticipate gale force winds with storm force
gusts and areas of rain and snow tracking along the Bering Sea
and Aleutians, including the Pribilof Islands today. The front
weakens as it approaches the Southwest Coast Tuesday and light
precipitation will linger through Wednesday. Daytime temperatures
at or just above freezing along the Southwest coast will allow
for rain to mix with snow or a transition to all rain, minimizing
the threat of blowing snow.

&&


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

A front extending across the Gulf from the Alaska Peninsula
across Kodiak Island moves across the Gulf by Saturday. The upper
level ridge over the Alaskan Interior weakens and falls back into
British Columbia by Saturday. This allows a moderately strong low
pressure center to advance from the Central Bering into the
Western Gulf of Alaska by the end of the forecast period. Models
are well clustered early but require the ensemble means to work
out the changes in tracks and strength by late Saturday into
Sunday. The Bering low picks up North Pacific moisture and forms
a front that will extend across the Gulf for Saturday through
Sunday.

Gusty Western Bering surface winds spread over the Aleutians
through Friday when they move out into the North Pacific. Locally
heavy rainfall associated with a second front connected to the
Bering low spreads over the Aleutians and Bering and Pribilofs
through Friday, and into Southwest Alaska and the AKPEN and into
the Gulf by the weekend. This front continues Eastward, bringing
potential for widespread rainfall over Southcentral Alaska late
in the week. Rainfall is expected to remain nearer the coast,
with higher elevations inland seeing a small amount of new
precipitation. A new frontal system coming out of the Russian Far
East extends its weather over the Western Aleutians and Bering
late Saturday into Sunday.

Kutz

$$

.AVIATION...

PANC...Gusty southerly winds will finally die down early this
morning as pressure gradients slacken. Weak coastal ridging will
develop again today, leading to redevelopment of the Turnagain Arm
jet this afternoon. However, with higher pressure inland today,
there will be little northerly bend to the jet and the terminal
will be on the very northern periphery of winds. Still expect some
south to southeast winds to develop late this afternoon, but winds
will be notably weaker than on Sunday and shorter-lived. Down-
inlet flow will develop tonight, leading to a return to light
northerly winds.

Patchy MVFR clouds have developed in the Anchorage area early
this morning. Based on the wind direction, expect these low clouds
will likely remain north and east of the terminal, but can`t rule
out a very brief period of these clouds floating over the airport.
For the remainder of the TAF period VFR conditions will prevail,
largely due to the persistent low level east to southeast flow
across the mountains. There is a chance of showers, especially
this afternoon through tonight as an upper low and trough move
into Cook Inlet. However, even if there are showers at the
terminal, the ceiling/vis would likely still remain VFR.

&&


$$