Gale Warning 204, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
512 PM AKST Wed Feb 21 2024

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

A broad and impactful low pressure system in the Central Bering
has pushed a pronounced frontal boundary across the Alaska
Peninsula and is now beginning to impact much of Southcentral.
Currently, this front is bringing precipitation across the
southeastern edge of the Kenai Peninsula and Western Prince
William Sound, however this system will rapidly advance northward,
bringing cooler temperatures and moisture to almost all of
Southcentral.

Through Thursday morning the southerly push of moisture and winds
will come to Thompson Pass and surrounding areas, to the north
along the Richardson Hwy, and to the south in Valdez. The highest
accumulation is expected to occur along the Richardson Hwy just to
the north of Thompson Pass where 12 to 24 inches of new snow
beginning late this afternoon and persisting until early Thursday
afternoon. This system is also expected to bring another round of
strong winds to Anchorage and the Mat Valley, with gusts late
tonight between 40 and 60 mph for Anchorage and the Mat Valley.
There is still notable disagreement between guidance regarding
which airmass will prevail, the incumbent warm air being fed
through the eastern gaps and passes, and the colder air moving up
Cook Inlet. This disagreement leading to higher uncertainty in
precipitation type and amounts in and near the Anchorage area.
There is likely to be at downslope warming through early tonight
due to the strong southeasterly winds, but precipitation in the
form of snowfall is expected to fill in as cold air advection
increases and winds turn southerly/southwesterly. For now, light
snow accumulations are expected in the Anchorage Bowl, with
slightly higher amounts of up to 8 inches possible on the
Hillside. Similar to Anchorage, Palmer's snow forecast is tricky,
depending on the timing of the Knik Arm warm air shut-off,
allowing for cooler southwesterly flow to prevail. Currently,
Palmer should expect about 3 to 6 inches of wet snow overnight
tonight.

Areas of higher forecast confidence for snow totals include the
Susitna Valley and along the Richardson Highway from Thompson
Pass north to Tonsina. Please see the associated
Advisories/warning for those areas.

The bulk of the precipitation across Southcentral ends by
Thursday evening as the main shortwave pushes through, but some
light upslope precipitation and showers may persist/start back up
by Friday. While the exact details are uncertain at this time,
another shortwave swinging around the main upper low will bring
another round of precipitation to Southcentral for Friday into
Saturday.

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

Key Messages:

High Winds for the Aleutians

-  High Wind Warning remains in effect for the Western Aleutians,
including Attu, Shemya, and Amchitka through late tonight.
Anticipate southwest winds 50 to 75 mph with gusts up to 85 mph.
Expect snowfall to reduce visibility to quarter mile or less at
times. Snow totals around 2 to 4 inches through tonight.

- High Wind Warning is also in effect for the Central Aleutians
including Adak and Atka this evening through Thursday morning.
Expect southwest winds 40 to 60 mph with gusts to 80 mph. Expect
reduced visibility with blowing snow. Around two inches of snow is
expected through tomorrow morning.

Discussion:

A complex low is developing over the Bering Sea as a Kamchatka low
moves into the far western Aleutians near Attu and Shemya, and
numerous lows along its frontal boundary deepen over the northern
Bering. One of these surface lows near St. Matthew Island enhanced
winds across Southwest Alaska resulting in near blizzard to blizzard
conditions over the Kuskokwim Delta and Nunivak Island earlier
today. Temperatures have since warmed and winds are gradually
decreasing as the front lifts north across western Alaska. As such
the Blizzard Warning was allowed to expire this afternoon as has the
Winter Weather Advisory that was out for the greater Bristol Bay
area. Much of the precipitation near Bristol Bay has changed over to
more of a rain/snow mix to all rain as temperatures climbed into the
mid and upper 30s this afternoon with some pockets of snow.

Looking back to the west...The Kamchatka low that was progged to
quickly deepen as it neared the western Aleutians has
underperformed. Models had this low and another compact low, that
would develop just east along the front, merging with a resultant
deepening of the low. It appears, however, that this second low
has not quite merged with the Kamchatka low and instead these two
lows have pushed east towards the western Aleutians as mostly
separate entities. The first low pushed through earlier today with
winds gusting up to about 60 kts at Shemya. The second low is
currently moving over the islands this afternoon and may still
allow for some winds gusting up to 65 to 70 kts. As such, have
decided to keep the High Wind Warning in place to see how this
second low develops heading into this evening.

The aforementioned low will continue to push through the Aleutians
and southern Bering bringing strong winds and precipitation to the
Central Aleutians late tonight through tomorrow morning. The low
will weaken as it nears the AkPen and gets swept up into the
southern periphery of the more dominant low deepening in the
northern Bering. Portions of the AkPen and Bristol Bay will likely
see another round of light snow as this system moves into tomorrow.
Otherwise, widespread scattered showers will reside over the Bering
and Aleutians the next few days as colder air starts to push into
the Bering and Southwest.

- PP

&&

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

A moderate amplitude pattern continues across the forecast area
through Wednesday. Forecast confidence remains good with good
ensemble support through midweek. A significant shortwave exits
the Mainland with a ridge close behind, pushing across the state
by Tuesday. This brings gusty surface winds with local gale force
winds to the Barren Islands and the Western Gulf through late
Sunday. A well developed surface low brings gusty winds with local
areas of gale force over the Western Aleutians Sunday, moving
into the Bering and diminishing. Ahead of this low, widespread
rain and snow over the Central and Eastern Aleutians for Sunday.
Another series of shortwaves sweep over the Bering and over the
Mainland to re-establish a trough from the Arctic through the
Interior to the Gulf of Alaska by Wednesday. The Western Aleutian
low moves across the Bering into Western Alaska by Monday,
spreading another round of strong winds over Bristol Bay, the
Alaska Peninsula and into the Gulf for Tuesday and Wednesday.

Kutz

&&

.AVIATION...

PANC...The winds is at the center of all the weather activity
through tonight and then things should settle down on Thursday.
Strong southeasterly winds are expected to peak this evening
through a little after midnight. During this period of strong
southeast winds is the period of most uncertainty for
precipitation amount and type. While temperatures aloft are
generally cold enough for snow, the warm air moving in off of
Turnagain Arm is likely to keep precipitation mostly rain or a mix
of rain and snow until winds turn southwest. When winds turn
southwest, all precipitation after that will be snow. However, by
that time the majority of the moisture will be east of Anchorage
so snowfall amounts are expected to be 2 inches or less at the
airport.

&&