Gale Warning 196, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
549 AM AKST Mon Feb 19 2024

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

Key points:

* Moderate to heavy rain expected in Southcentral upslope areas
  and along the coast through Tuesday

* Strong southeasterly gap winds of at least 40 to 60 mph expected
  Monday into Tuesday along the Anchorage Hillside

* Temperatures warming to 40+ degrees on both Monday and Tuesday
  across the Kenai Peninsula, Anchorage Bowl and Mat Valley.

* Precipitation potentially ending as mix/snow for Kenai P.,
  Anchorage and southern Mat-Su Tuesday evening, with rain and
  snow chances returning with another system late Wednesday into
  Thursday

Discussion:

South/southeasterly upslope flow continues light rain/showers
across the Southcentral coast throughout the day today ahead of
our next few systems, with typical downslope areas remaining
mostly dry.

The first shortwave feature of note over Bristol Bay will
continue to swing northward around an upper level low over the
Bering this afternoon. This will begin to pull up a deep plume of
moisture to over the western Gulf, increasing light to moderate
precipitation across Kodiak Island and through the typical upslope
areas in the northern and western Susitna Valley and Prince
William Sound later this morning into this evening. At the same
time, a ridge begins to build in the Gulf and shifts eastward over
Southeast Alaska by Tuesday morning. A strong west-to-east
thermal gradient and associated pressure gradient will develop
between these two features over Southwest Alaska on Monday. The
first round of strong southeasterly gap winds are likely to impact
Southcentral starting Monday and the higher elevations, including
the Anchorage Hillside, are likely to experience winds gusting
over 40 mph. The Turnagain arm winds are expected to temporarily
bend into south and west Anchorage Monday evening, bringing a
period of gusty winds. Similar warm winds will move through the
Knik Arm and Copper Valley. Strong jet dynamics, thermal gradient,
and vorticity advection associated with another shortwave will
then allow a stronger low to develop and deepen along a front in
the North Pacific, moving northward into Bristol Bay by Monday
night. While there are still timing differences, the southeasterly
gap winds are likely to become even stronger by Tuesday afternoon
as the low crosses 60N, potentially peaking at 60+ mph along the
Hillside. The associated southeasterly flow will also allow high
temperatures to breach 40+ degrees on both Monday and Tuesday
across the Kenai Peninsula, Anchorage Bowl and Mat Valley.
Generally speaking, this low is weaker and slower than indicated
yesterday, so the threat of 75+ mph winds on the Hillside has
lessened.

As the front and main shortwave axis finally push through Tuesday
night, the strong gap winds will come to an end and cold air
advection and up inlet flow may allow precipitation to fill in
briefly and end as a mix or snow across the Western Kenai
Peninsula, Anchorage Bowl and Mat Valley.

As we approach the latter half of Wednesday into Thursday, a
large upper low over the Bering Sea will push another system into
Southcentral, likely bringing another period of widespread
precipitation. This system will be notably colder, so the threat
of moderate to potentially heavy snow returns.

-ME

&&

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

On satellite imagery (CIMSS MIMIC PW) there is a fetch of moisture
that originates west of the Hawaiian Islands and extends
northeast to the Alaska Peninsula and Bristol Bay. There is a
second plume of moisture that extends from the West Pacific basin
to Northern Japan and Kamchatka. These 2 plumes of moisture will
bring precipitation to the state of Alaska and are actively being
monitored. The models continue to project a highly progressive and
dynamic pattern for the Aleutians, Bering and Southwest Alaska.
Expect more unsettled weather which will include gusty winds,
precipitation and enhanced seas. This morning there is at 3AM AKST
or 12Z a surface low entering Bristol Bay, a surface low north of
Adak, another surface low south of Adak and a low southwest of
Kamchatka. The radars at King Salmon and Bethel have been active.
Today and Tuesday will be wet for Southwest Alaska. It has been
snowing at Dillingham early this morning but it has been raining
at King Salmon. The P-type is going to continue to be tricky for
the region. The chain is going to be showery. And the next
stratiform event for the western Aleutians will be on Tuesday.

&&

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

The long duration upper level Bering low weakens and begins an
Easterly track through Interior Alaska, and forming a weak center
over the Gulf by the end of the forecast period. Consistent
forecast model positions, strengths and tracks will hold through
the weekend. Tightest gradients remain along the Southern
periphery, providing the axis of movement for the transient
systems supported by short waves along the Aleutians and across
Southern Alaska. Widespread gale force winds with storm force
gusts spread along the Aleutians before diminishing. Gusty winds
remain an issue across the Bering into the Gulf of Alaska through
Sunday. These transient fronts and troughs bring locally heavy
precipitation across the Aleutians, AKPEN and Southwest Alaska.
Mostly rain on the Pacific side, mixed rain and snow or all snow
on the Bering side through Friday. Colder temperatures for the
weekend expands the areas for snow through Sunday. After a
shortwave ridge moves over the Bering, another upper level low
moves out of the Russian Far East.

Longer term and locally heavy precipitation continues along the
AKPEN coast into Cook Inlet and over Kodiak Island, and expands
along the Southern Coast to the Canadian border through late
Friday, tapering off slowly afterwards. Onshore flow will be
deepest through Prince William Sound and Copper River Valley. Rain
dominates the coastal areas, with lesser amounts over higher
elevation inland. Mixed rain and snow at lower elevations across
Southcentral Alaska progressing to all snow further inland. The
above average temperatures across Southern Alaska linger before
making the turn colder through the weekend.

Kutz

&&

.AVIATION...

PANC...VFR conditions and light northerly winds will persist
through late this morning. A light to moderate Turnagain Arm wind
is expected to move over the terminal early this afternoon as a
low moves into western Alaska. The Turnagain Arm wind may move out
of the terminal late tonight as another low develops to the
south. Meanwhile, strong southeasterly winds will persist aloft,
which may result in LLWS. Should the wind stay over the terminal,
no LLWS is expected.

-ME

&&