668
FXAK68 PAFC 241312
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
412 AM AKST Sun Nov 24 2024

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

The influence of the ridge that has encompassed much of the
southern Mainland this past 4-5 days is waning as a trough moves
in from the west. For today, cloud cover will steadily increase
from west to east, leading to rising temperatures in the lower
elevations and cooling temperatures aloft as a strong temperature
inversion breaks down. With the slight influence of the ridge
remaining, fog and/or low stratus has been seen throughout the
Anchorage area.

The trough will influence the area starting tonight, with
southwesterly flow and lift induced by the trough, bringing light
snow to the far northern Susitna Valley as early as this evening,
with higher confidence of more moderate and widespread snow early
Monday morning. With the southwesterly flow, the Mat-Su will
likely get the most snowfall from this system with 4-8 inches,
and lesser amounts of 1-3 for Anchorage and the eastern Prince
William Sound. For the Mat-Su, there should be a strong upslope
component to the snowfall for south and west facing areas. This
means areas along and east of the Parks highway for the Susitna
Valley, and near Hatcher Pass, Fishhook and Sutton for the Mat
Valley. The primary uncertainties for snow amounts have to do with
the timing of saturation, and whether or not a trailing shortwave
will linger snowfall an additional 3-6 hours along western facing
slopes.

By Tuesday morning this system should be departing, with any
remaining precipitation mostly over the higher terrain. An
additional shortwave dropping south over Southcentral from the
northwest Arctic will reinforce more cold air, dropping
temperatures well below normal once again. Strong winds are once
again likely to develop through Seward, Whittier and Thompson
Pass, and may develop in the Mat Valley and Valdez depending on
the path of the upper level feature. Otherwise, expect clear and
cold weather to return by mid-week.

-CJ

&&


.SHORT TERM FORECAST SOUTHWEST ALASKA AND THE BERING SEA/ALEUTIANS
(Days 1 through 3: Today through Wednesday morning)...

An area of low pressure in the northwestern Bering Sea south of
the Gulf of Anadyr continues to push eastward today to between St.
Matthew and St. Lawrence Islands by this afternoon. The frontal
system associated with this low, currently across the Yukon and
Kuskokwim Deltas, will continue to push further inland today.
Pockets of light freezing rain are possible in the Lower Kuskokwim
Valley today as the cold air at the surface will be stubborn to
depart with warm air aloft working in. Meanwhile, the Kuskokwim
Delta region should continue to rise above freezing at the surface
through the day. With that, a Winter Weather Advisory remains in
effect until 6AM AKST early this morning for the Kuskokwim Delta.
This advisory should be allowed to expire as most locations are
above freezing and will continue to warm through the day today.
The one cold location is Kalskag which is in the upper 20s
currently. There is some potential for light freezing rain there
this morning as warmer air works in aloft; however, any freezing
rain will be short-lived before a transition to rain. A Winter
Weather Advisory for the Lower Kuskokwim Valley also remains out
through the afternoon hours with freezing rain most likely to
occur near Aniak and Chuathbaluk. Areas further inland, like
Sleetmute and Lime Village, should remain cold enough for snow.
This system continues eastward and starts to impact Southcentral
Alaska for Monday, while snow showers along the Western Alaska
Range continue with upslope westerly to northwesterly flow behind
it. Northerly to northwest flow will be the dominant weather
player for Southwest Alaska starting on Monday and continue
through Wednesday. This setup looks to lead to colder and drier
conditions across the area.

Farther out west, the tail end of the front impacting mainland
Southwest today, departs the Pribilof Islands this morning, and
could clip the Eastern Aleutians later this morning into the
afternoon with a few light showers. Meanwhile, a shortwave ridge
over the Western Aleutians will begin to weaken today and move
further north into the Bering Sea while a North Pacific low pushes
its front northwestward towards the Central and Western Aleutians
by this evening. Steady rain across is likely across those areas
tonight through Monday. The low itself lifts northward to the
vicinity of the Central Aleutians by Tuesday morning with a
resurgence in steady rain likely. Persistent showers are also
likely for the Eastern Aleutians through Tuesday with rain making
it to the Southern Alaska Peninsula (AKPEN) by Tuesday afternoon.
There is some uncertainty with where this North Pacific low will
track and evolve past Tuesday afternoon. Some solutions push the
system further into the Bering Sea (Canadian/ECMWF) while other
guidance lingers the system in the North Pacific through Wednesday
morning (NAM/GFS). The further north track would give places like
the Pribilof Islands the potential for steady rain while the
southern solution of linger in the North Pacific would keep them
mainly dry through Wednesday but give more precipitation to the
southern AKPEN.

&&

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

Significant weather changes are expected over Alaska throughout
the long term period, with evolving dynamics in the North Pacific.
The period begins with a ridge of high pressure over the Bering
Sea and a positively tilted trough digging over eastern Alaska and
the Yukon. A large upper-level low over the North Pacific is the
key player, but models differ in its progression. The GFS
indicates the trough will deepen, allowing the North Pacific low
and additional shortwaves to move northeastward, spreading more
widespread precipitation across the region, particularly along
the coast. In contrast, the ECMWF suggests the initial trough
evolves into an upper-level low over mainland Alaska, shunting the
North Pacific low southward and leaving much of Southwest Alaska
and parts of Southcentral Alaska drier during the period.

Regardless, gale-force winds are expected to continue over the
Bering Sea early in the period. Snow is also expected to spread
across Interior Alaska by Wednesday, reaching near the
Southcentral coast with coastal areas east of Prince William Sound
potentially seeing a mix of rain and snow. Depending on how the
North Pacific low progresses, as suggested by the GFS and other
guidance, moderate rain and snow could develop near the eastern
Aleutians and AKPEN by Friday and potentially spreading towards
Kodiak Island and the Southcentral coast by the end of the period.
However, with model disagreement, there remains uncertainty in
the exact timing and extent of precipitation, though there is a
strong signal for impacts at some point.

Eovino


&&.AVIATION...

PANC...There is a chance for fog development over night into early this
morning. Fog chances should dissipate by mid/late morning, with
only a few low hanging clouds leftover. VFR conditions and light
winds are expected for most of the afternoon and evening hours.
Conditions Begin to deteriorate tonight, with snow moving in
around 10Z, dropping visibilities and cloud ceilings to low MVFR.
Winds are expected to shift southeasterly around the time snow
begins and increase to around 12 knots.

&&



$$