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FXAK68 PAFC 211314
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
514 AM AKDT Tue May 21 2024

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

A weak upper level ridge that currently dominates the eastern
Gulf of Alaska and Eastern Alaska will continue to slowly drift to
the east as a deep and cold for the season upper level trough
over the Eastern Bering Sea and Western Alaska slowly progresses
to the east. An anchoring low in the trough currently near the
Pribilof Islands will weaken as it pushes northeast to be located
near Nunivak Island by Wednesday morning. The upper level low
will continue to weaken and elongate and will stretch from near
the Gulf of Anadyr south and east to near Kodiak Island by
Wednesday night.

Several shortwaves will rotate around the upper level low and will
bring periods of rain for the AKPen, Kodiak Island and
Southcentral through the day today and tonight. A front rotating
around the low currently located in the eastern Bering, will
push north of Kodiak Island later this morning and will push into
the southern Portions of the Kenai Peninsula this afternoon.
Expect widespread rain and snow over much of the area, with some
locations receiving heavier rates of precipitation at times on the
Eastern Kenai Peninsula and into Prince William Sound.
Southwesterly flow aloft will allow the Anchorage Bowl to get some
precipitation Tuesday afternoon as the front passes.
Additionally, a building pressure gradient across much of the
Chugach and Kenai Mountains will produce southerly gap winds near
the Kamishak Gap, Turnagain and Knik Arms, and the Copper River
Basin starting this morning and extending into Wednesday.

As the upper low continues to move eastward into the mainland, a
secondary cold front will start extending out ahead of the low
Wednesday into Thursday. This will cause temperatures to drop
below normal for most locations, increasing the potential for snow
to occur at some lower elevations as snow levels decrease. Latest
model guidance continues to indicate a deformation band setting
up over Cook Inlet, the Anchorage Bowl and the MatSu which will
serve to increase precip totals in those areas. A chance for rain
and snow showers will persist through Thursday afternoon before
the low starts to weaken and move eastward towards Canada.

-CC

&&

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

Active weather continues as two weather systems are poised to move
across the Bering Sea, Aleutian Islands, and Southwest Alaska
through Thursday. Forecast confidence is moderate to high due to
good model agreement, with precipitation type being the biggest
forecast challenge as cold air moves in aloft. No major hazards
are currently being monitored.

The first weather system features an occluding low near the
Pribilof Islands, with its front extending across Southwest
Alaska. A stout upper level shortwave rotating around the low has
led to an intensification of rain rates along the front this
morning, with radar showing moderate to heavy rainfall with
reflectivities as high as 50 dBZ. Up to another 0.5" of rain are
expected (with locally higher amounts possible) as the front
moves east across Southwest Alaska through today, with the
greatest amounts expected for Bristol Bay and Lower Kuskokwim
Valley. Winds have also picked up with the intensification of the
front; gusts of 30-35 kt are currently being observed as winds
channel through Kamishak Gap and across both interior Bristol Bay
and the Lower Kuskokwim Valley.

For the Bering Sea and Aleutian Islands, gusty winds are also
forecast as vorticity and cold air advection help enhance winds. A
wide swath of westerly winds sustained at small craft speed (25
kt), with a small area of gales (35 kt), will move across the area
through today. Scattered showers are also expected across the
Aleutian Islands, with more frequent showers expected for the
Pribilof Islands nearer the low center. Conditions gradually
improve through today for the Bering Sea and Aleutian Islands as
the low exits into Southwest Alaska. For Southwest Alaska, the
incoming occluded low will mean a continuation of precipitation
through Wednesday even as the front exits the area. Expect showers
to be widespread, especially as another shortwave moves in off
the Bering Sea and helps to enhance precipitation.

A second low and its front move into the Western Bering and
Aleutians by tonight, signaling a quick return to wetter weather.
Winds will be a bit stronger, with a broader swath of gales
wrapping around the low and moving across the Western and Central
Aleutians through Thursday. With cold air lingering in the Bering
Sea courtesy of today`s low, there is a chance for very light snow
accumulations for the Pribilof Islands and Kuskokwim Delta
coast/Nunivak Island as the front moves through. Precipitation
type is a little uncertain, but either way, no more than a light
dusting of snow is expected.

-KC

&&

.LONG TERM FORECAST (Days 4 through 7)...

Friday, an upper-level low over the eastern Bering drops across
Southwest Alaska and into the Gulf by Saturday afternoon. A
trough sets up over the western coastline bringing possibly mixed
rain and snow for the Western coastline and all rain elsewhere,
primarily to Kodiak and the eastern Kenai. A high pressure ridge
forms across the Bering before the next upper-level low
consolidates and moves eastward from the vicinity of Attu Island
on Monday.

&&

.AVIATION...

PANC...A trough arriving from Southwest Alaska this morning will
bring light rain and the potential for MVFR conditions through
much of the day. Winds are expected to increase out of the
southeast through the afternoon hours as the pressure gradient
over the region tightens and the Turnagain Arm wind becomes more
prominent. Southeast gusts as high as 40 knots over the Upper
Hillside and over Cook Inlet should be more manageable for PANC at
15 to 25 knots.

-BL

&&


$$