Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 211320
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
520 AM AKDT Thu Mar 21 2024

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

The high amplitude ridge that has been parked over eastern Alaska
and much of the Gulf will begin to shift eastward today with axis
positioning itself over the ALCAN border by early Friday morning.
Stratus and localized patchy fog have been prevalent across the Gulf
and up into the Cook Inlet this morning; however, more widespread
fog has yet to develop as stratus holds steady and higher cloud
cover works in. The Copper River Valley may yet see some fog develop
a bit later this morning with ridge axis positioning overhead and
relatively clear skies. Temperatures will remain fairly mild today
despite increasing cloud cover ahead of an approaching trough.

The aforementioned trough will take on a negative tilt as it lifts
towards the AKPen tonight. While models show modest forcing in the
mid and upper levels, the lower levels continue to struggle with
only a weak surface low progged to form along the eastern Kenai
Peninsula and a weak attendant front. Precipitation still looks to
be focused on Kodiak Island, and the southern and eastern Kenai with
decreasing chances further north. If any precip does make it up into
the northern Cook Inlet, Anchorage Bowl, and Mat-Su Valley...it will
be light. The other forecast challenge will be precipitation type
with temperatures hovering near freezing to several degrees above
freezing. Without a decently cold airmass in place, mild southerly
flow aloft, and precipitation working inland during the daytime
hours...we may have a difficult time supporting all snow.

The Copper River Basin could see an additional day of warmer
temperatures on Friday as the thermal ridge axis moves over the
Basin. Could see temperatures once again approach the 40 degree mark
in Gulkana and Glennallen areas. Shortwave ridging will move into
Southcentral behind Friday`s system and will make another mild day
on Saturday with temperatures pushing the upper 30s to mid 40s for
many areas. A stronger system will lift towards the Bering from the
North Pacific on Saturday. The front will lift north across the Gulf
with swath of precipitation favoring the southern AKPen, Kodiak
Island, and the eastern side of the Kenai Peninsula by Saturday
afternoon/evening.

- PP

&&

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

Key Messages:

* A Flood Advisory remains in effect through this afternoon for
  Unalaska and the surrounding area. Additional rainfall amounts
  up to 0.5 to 1 inch are expected.

* Warm and soggy conditions continue through end of week as
  persistent southerly flow and multiple waves of moisture bring
  up to 1 to 2 inches of rainfall to the Eastern Aleutians and
  the Alaska Peninsula through Friday night.

* 1 to 3 inches of snow across the western Kuskokwim Delta and
  Nunivak Island through Thursday.

Discussion:

A reinforcing shortwave and southerly flow continue to draw deep
moisture northward as strong vorticity advection and jet dynamics
allow a low to form along a boundary just south of the Central
Aleutians through today. As this low pushes eastward, anticipating
areas of moderate to locally heavy rain to develop along the
eastern the Eastern Aleutians and the Alaska Peninsula, especially
along the Pacific side. Southerly gale force gap winds are also
likely to develop again across the eastern Aleutians and Alaska
Peninsula.

In addition, light to moderate snow accumulations up to 3 inches are
possible across the western Kuskokwim Delta and Nunivak Island
through tonight. From Kwigillingok eastward, any precipitation
will likely be in the form of light rain or a rain snow mix.
Precipitation type for the Pribilofs remain a forecast challenge,
with model guidance diverging on the track and intensity of the
surface low between the Pribilofs and the Western Alaska. GFS
solution seems to be the outlier and has trended with a more
compact low and slower trend, while other solutions keep a more
progressive and weaker track towards St. Lawrence Island.
Continued with a low confidence model blend for this forecast
package, resulting in very light snow accumulations for the
Pribilofs through mid afternoon.

Overall, with the persistent southerly flow, high temperatures
near sea level over the next few days will likely push well into
the 30s to near 40, except near the Pribilofs and Kuskokwim Delta
where a reinforcing cold shot behind the departing low may cause
temperatures to struggle to rise above freezing on Friday.

&&

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

The upper level pattern over the region shows a broad trough
extending across the Bering from the Arctic to the North Pacific.
This pushes its way into the Western Mainland through the forecast
period. The high center over the Eastern interior weakens and
slips into the Canadian Provinces, with only a ridge remaining
over most of the state through Wednesday. Continued warmer
temperatures are on tap across the Mainland.

The broad trough supports a series of surface lows pressing
Eastward along the front over and just South of the Aleutians. A
well developed low South of the Pribilofs and its front moves
across the Southern Aleutians and Bering through Wednesday. This
low settles into the Southeastern Bering through midweek.
Widespread precipitation over the Aleutians and Bering into
Western Alaska expected, with locally heavy precipitation with the
frontal waves. Gusty Northerly winds spread from the Central
Bering West Sunday and Monday and continues across the Aleutians
through Tuesday. A developing North Pacific low brings another
round of precipitation and gusty winds to the Western Aleutians
Tuesday and Wednesday.

The Bering front extends over the Gulf of Alaska, moving to the
North Gulf Coast by late Monday. Locally heavy rainfall will occur
from the Alaska Peninsula across Kodiak Island through Sunday,
over the Kenai Peninsula through late Monday, into Prince William
Sound and the Copper River Valley through Tuesday. After a brief
break, a second front spreading across the Southwestern Gulf for
late Tuesday into Wednesday.

Kutz

&&

.AVIATION...

PANC...Southwesterly flow continues up Cook Inlet this morning.
Therefore, continue to expect ceilings to bounce around VFR and
MVFR levels through the day. Visibility should remain VFR with
light winds. Looking ahead, a weak frontal system lifts northward
through Friday with the possibility of more persistent MVFR
ceilings at the end of the TAF period and into Friday evening. The
one thing working against this is light southeasterly flow in the
lower levels of the atmosphere which could help keep conditions
drier.

&&

$$


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