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FXAK68 PAFC 260120
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
420 PM AKST Mon Nov 25 2024

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

Precipitation for much of Southcentral is winding down this
evening as this morning`s upper trough exits the region to the
east. Southcentral will remain in broad cyclonic flow aloft
through the end of the week with additional shortwaves forecast to
dig southward into the Gulf. This will likely allow for snow
flurries to fall from the Mat-Su Valley down through the Turnagain
Arm into tomorrow afternoon, though little to no accumulation is
expected. It also means that lingering cloud cover will slow down
the expected cool down across Southcentral. High temperatures on
Tuesday will range from the teens across the Copper River Basin to
the mid 20s through the Mat-Su, Anchorage Bowl, and Kenai
Peninsula. The warm spots will be from Valdez into Prince William
Sound with highs in the low to mid 30s. Tuesday`s morning commute
may experience fog along the Glenn Highway from Wasilla down into
Anchorage.

Clearer conditions are anticipated Tuesday night into Wednesday,
which should allow for more robust cooling across Southcentral.
The Copper River Basin will see areas dip into the single digits
while the Mat-Su, Anchorage Bowl, and western Kenai Peninsula will
see daytime highs only warm into the teens. As typical with cold
air advection we expect gap winds to increase in the usual
locations (Resurrection Bay, Passage Canal, Valdez/Thompson Pass,
etc.) with various peaks through the latter half of the week, as
additional shortwaves pushing through the region support an
increase in northerly flow. The strength of a Matanuska Valley
wind will be greatly dependent upon how far east the upper level
low tracks across Southcentral on Wednesday and Thursday. There is
model disagreement here, and it is something we will keep a close
eye on.

&&


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

Key Points:

* Snow showers continue in Lower Kuskokwim Valley, Western Alaska
  Range, and Kuskokwim Mountains tonight

* Colder and drier conditions expected for Southwest Alaska
  through at least Thursday. Heavy Freezing Spray likely along
  Kuskokwim Delta coast near ice edge Tuesday evening into
  Wednesday morning

* North Pacific low brings rain, gusty winds, and gale-force
  conditions to the Aleutians; rain/snow mix possible for Pribilof
  Islands Tuesday

Upslope snow showers will continue through early tonight in the
Lower Kuskokwim Valley, particularly along the Western Alaska
Range as well as along the Kuskokwim Mountains in the Kuskokwim
Delta region. Northerly to northeasterly flow for Southwest Alaska
Tuesday through Thursday will lead lead to colder and drier
conditions across the area. With the persistent off-shore winds
expected, Heavy Freezing Spray is likely Tuesday evening into
Wednesday morning along the near shore zone of the Kuskokwim
Delta, especially near the ice edge and through Etolin Strait.

Farther west, a North Pacific low continues to send its front
northwestward across the Central and Western Aleutians, with
steady rain and gusty conditions occurring. At the same time,
widespread gradient-driven gale-force winds are developing across
the central and western Bering Sea. These winds will become
widespread on Tuesday along with storm-force gusts Tuesday morning
into Tuesday afternoon before the gradient between the North
Pacific low`s front and high pressure to the north in the northern
Bering begins to relax.

Meanwhile, showers will make it to the southern Alaska Peninsula
by this evening and into Tuesday morning. There is some better
agreement today in regards to the low track and northward extent
of precipitation for the Pribilof Islands, with a period of steady
rain becoming increasingly likely later on Tuesday into Tuesday
night. There is still more uncertainty in regards to precipitation
type as well, especially for Saint Paul, but a period of
rain/snow mix is possible Tuesday evening. Regardless, this area
of low pressure will end up weakening and transitioning into
frontal system as it moves west across the chain into Wednesday
afternoon. With that, more light rain will be possible for the
Central and Western Aleutians into Thursday as another stronger
North Pacific low sends it front northward towards the Chain by
then. However, there is still notable uncertainty in the northern
extent of precipitation and wind impacts from Thursday`s system.

-ME

&&

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

A colder, and drier pattern looks to set up across most of mainland
Alaska by late this holiday week and continuing through the weekend.
The blocking pattern will begin to break down by mid to late week as
an upper level trough surges southwards and elongates into Southwest
Alaska before deepening over the Bering Sea this weekend. Surface
ridging will remain entrenched over much of the mainland, keeping
temperatures well below normal. Any precipitation that occurs will
be light and mainly terrain induced, or tied to seeder-feeder
processes as several shortwave troughs pass through.

While the mainland looks to stay mostly dry throughout the extended
forecast period; the Aleutian Islands, AKPen, and the coastal
regions across the Gulf of Alaska will see a wet and fairly mild
pattern set up. A North Pacific low will lift up towards the central
and eastern Aleutians before getting blocked by the trough dropping
southwards into the Bering. As such the North Pacific low will then
to forced to skirt along the southern periphery of the Aleutian
Chain and the western Gulf. A modest surge of moisture will
accompany the low, with widespread rainfall expected across the
Central Aleutians and AKPen. Precipitation will then spread into the
Gulf and associated coastal areas by the upcoming weekend.

- PP

&&

.AVIATION...

PANC...Persistent cyclonic flow aloft, upslope flow along the
Chugach Mountains, a moist boundary layer (with drying conditions
aloft) all point toward low clouds persisting at and near the
terminal. The flow tends to favor the lowest conditions right up
against the mountains. Based on this, have gone with prevailing
MVFR ceilings for the terminal. However, suspect there will be a
period of IFR ceilings - it`s just very difficult to say when that
will be. Atmospheric flow will shift to northerly Tuesday afternoon
through Tuesday night, which should lead to arrival of drier low
level air and lifting of ceilings.

-SEB

&&


$$