Gale Warning 389, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
441 PM AKDT Mon Apr 15 2024

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

A strong upper level ridge has brought clear skies across most of
Southcentral this afternoon. Later this evening, the ridge axis
will shift east towards the AlCan border, allowing southerly flow
to strengthen between the ridge to the east and a low over the
Bering Sea. Cloud cover will begin to increase as moisture from
the Gulf is pulled northward through Tuesday morning. However, any
rain/snow will be focused on the windward side of high terrain
for the eastern Kenai Peninsula and western Prince William Sound.

Tuesday evening a more active pattern develops, as a large North
Pacific low slowly progress north towards the AKPen through mid
week. This low will advance a strong front and attendant moisture
stream north into the western Gulf, spreading strong easterly gale
force winds with storm force gusts across the southwestern two
thirds of Gulf waters by Wednesday morning. The bigger impact from
this system will be moderate to locally heavy precipitation rates
spreading across Kodiak Island. Temperatures could be cold enough
in the low to mid levels for initially a rain snow mix to move
into Kodiak at sea level on Tuesday afternoon/evening, but otherwise
steady, moderate rain is expected to begin around this time and
persist into Thursday. Total rainfall amounts of 3 to 5 inches
will be possible along the southeastern side of Kodiak Island.
Lighter rainfall amounts, generally less than an inch will be
possible along the southeastern Kenai Peninsula during the same
timeframe, including Seward.

Most of the remainder of Southcentral will remain dry but
steadily cloudier through Wednesday night. Strong easterly gap
winds are expected to develop along the Turnagain Arm Tuesday
night through Wednesday night.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA, BERING SEA, AND ALEUTIAN
ISLANDS (Days 1 through 3: Tonight through Thursday)...

An upper-level trough parked over the Bering Sea continues to
support the active pattern over the area. A compact low pressure
system in the Bering Sea is quickly moving north out of the area.
However, on the eastern boundary of the low, a strong front is
pushing up across Nunivak Island and across the Kuskokwim Delta,
bringing gusty winds with snow, leading to blowing snow. A Winter
Weather Advisory remains in effect for the area, with conditions
expected to slowly begin improving by midnight tonight. Gusty
southerly winds will continue pouring into the Kuskokwim Delta
coast through the night, but by Tuesday morning the core of
strongest winds will begin to weaken.

By Tuesday afternoon a lobe of the upper-level trough will begin
diving out of the northern Bering. This will bring a shot of cool,
dry, and gusty northerly winds into the Central Bering and Central
Aleutians. Gusty winds from this push are expected to be most
concentrated between Adak and Nikolski Tuesday night, however may
shift eastward into Wednesday morning, bringing gusty northerly
winds toward Unalaska and the Pribilof Islands. By Wednesday
morning, gusty winds up to 55 mph on the southern side of the
Aleutian Chain out of bays and passes will become more pronounced,
and are expected to persist into Thursday morning.

However, in Southwest Alaska the precipitation will continue into
Tuesday and Wednesday as the decaying frontal boundary becomes
bolstered by a north Pacific low approaches the southern Alaska
Peninsula late Tuesday into Wednesday morning. This system
represents part of the driving force behind the gusty winds in
the Central Bering. For Southwest Alaska it will push strong and
gusty easterly winds through the Kamishak Gap into interior
Bristol Bay by early Wednesday and will maintain the moisture tap
into the area. However, the air moving through the gap will be
warmer, gradually shifting the reinforced precipitation from snow
gradually to a rain/snow mix, and plain rain by Wednesday afternoon.
These gusty winds through Kamishak will likely continue into the
end of the workweek, continuing the gradual warm-up in Southwest,
shifting more of the widespread precipitation to rainfall
particularly for the Greater Bristol Bay area.

-CL

&&

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

The long term forecast begins late Thursday with a strong ridge
of high pressure situated over the Yukon and a negatively tilted
longwave trough extending southeast from the central Bering. A
vertically stacked low well south of the Alaska Peninsula Thursday
slowly lifts to the AKPen and eastern Aleutians through Friday.
A front attached to the low looks to remain nearly stationary
near Kodiak Island, allowing moisture to continue to stream toward
the island on southeasterly winds aloft from the eastern Pacific.
This moisture stream will likely result in several additional
inches of rain for parts of Kodiak Island through Saturday before
the front finally weakens and shears apart.

To the north, an inverted trough is the boundary between warmer
air over Southwest Alaska and a colder airmass over the western
half of the Bering and Aleutians. Precipitation will focus along
the trough axis, with rain for Southwest and a mix of rain/snow
to the west of the trough.

By Saturday, the ridge looks to extend across interior Alaska,
suppressing the trough to the south, along the Aleutians and
southern Gulf of Alaska. The ridge will likely lead to generally
quiet conditions for much of interior Alaska, including the
Southern Mainland. The exception would be along the immediate
coast, where a front lifting toward the northern Gulf may bring
some precipitation from Prince William Sound to the AKPen by
Sunday or Monday.

TM

.AVIATION...

PANC...VFR conditions will continue today. Increasing pressure
gradients between high pressure in the Gulf and the low and front
over western Alaska will lead to a strengthening Turnagain Arm jet
this afternoon and evening. There will be a weak northward bend,
which should bring some wind into the terminal - aided by steep
lapse rates right off the surface. Winds will weaken overnight and
shift back over the northern Inlet.

For Tuesday, the Turnagain jet will re-strengthen, though with a
front entering the southwestern Gulf, gradients will favor the
jet coming straight out of Turnagain Arm to Fire Island and the
northern Inlet. Still, as the sun warms up the surface, the
terminal will likely see some gusty southeast winds on the
northern periphery of the jet.

&&