987
FXAK68 PAFC 031325
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
525 AM AKDT Mon Jun 3 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Wednesday night)...

A long-wave trough extends across all of Alaska, with a zonal jet
stream centered between 40N and 50N latitude. A multi-centered
closed low circulation is located over the southern Gulf/Northeast
Pacific, with the much stronger vertically stacked low tracking
E-NE toward SE Alaska and British Columbia. This is helping to
shift the entire cyclonic circulation to the east with time. An
old frontal boundary, now just a surface trough, is weakening
along the northern to western Gulf coast. Winds and rainfall
along the trough are gradually diminishing. Kodiak City, which
has received over 5" of rain since Wednesday (May 29th), is
finally seeing a break in the rain, with just occasional sprinkles
or very light rain. Light rain is also being observed along the
north Gulf coast and Prince William Sound. A steady supply of
weak vorticity-maxima embedded in the upper low circulation are
tracking westward across Southcentral, then southwestward down
the Alaska Peninsula. With such weak and small scale features,
model guidance is really struggling with placement of precipitation.
In any case, precipitation early this morning is very light,
producing no more than a trace accumulation in most locations.

As we head through the day, expect breaks of sun to develop inland
and combine with the steady supply of vorticity-maxima to produce
isolated to scattered showers. Meanwhile, rain along the coast
will taper off. Tonight will be mostly dry, though cannot rule out
an isolated shower just about anywhere. Tuesday will start out dry
with some sunshine as a short-wave ridge passes overhead. However,
a stronger short-wave trough rounding the Gulf low (positioned
over the eastern Gulf at this point) will approach the Copper
River Basin Tuesday afternoon, leading to increasing clouds and
showers. The short-wave will march westward across Southcentral
Tuesday night through Wednesday bringing widespread soaking rains
to the region. Once again, the upper levels are quite complicated,
with numerous vorticity-maxima moving through the primary short-
wave. Models all look a little different with timing and track of
individual features. Based on the overall strength of forcing and
speed of the trough, expect rainfall amounts to range from about
one quarter to one half inch. However, upslope flow and instability
out ahead of this will most certainly lead to localized higher
amounts.

Forecast confidence drops Wednesday night and Thursday as model
spread grows large with the track of the Gulf low. All guidance
pulls the low back westward in response to a large deep cold low
dropping southward across the Bering Sea. However, models vary
on whether the upper low opens into a trough and whether is
stays over the Gulf or tracks over Southcentral. In any case,
considerable cloudiness along with the threat of rain will
persist, especially along the coast.

-SEB

&&


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

A low in the Gulf of Alaska is sending easterly shortwaves across
Southwest Alaska and helping to promote showers across the area
today. As the low continues eastward and an Arctic low pushes
south along the western Alaska coast, flow with these showers will
shift more northerly and bend the showery activity towards the
Kuskokwim Valley and into Bristol Bay. Later this afternoon, the
convergence of the easterly waves and the next trough moving
south, could bring added lift and produce isolated thunderstorms
for the Kuskokwim Valley, the Western Alaska Range, and interior
Bristol Bay.

Northerly flow will continue to prevail across the Bering Sea and
a surge of cold air ahead of the Arctic low will reinforce winds
across the central and eastern Bering Sea. The strongest winds, to
gale force, will likely occur near Nunivak Island and south of
the eastern Aleutians and the Alaska Peninsula tonight through
Tuesday. Winds will decrease though as the low continues to make
its way across the Pribilofs by Wednesday morning and slows in the
southern Bering.

Temperatures will cool off on Tuesday to around ten degrees
cooler than what is expected for today. Much of the cool air will
remain towards the Kuskokwim Delta and into the Bering Sea toward
the Pribilofs. Models are trending into better agreement with the
placement of the low and timing of the cool air, at least until
the cool air reaches the southern Bering Sea. Its extent east and
west will depend on how far west the low moves beyond midweek.
Temperatures will be cool enough for light snow or a mix of rain
and snow to be possible. No accumulation is expected. Expect on
and off showers to remain in the forecast for the short term.
Temperatures will begin to bounce back behind the low for most of
Southwest Alaska from midweek onwards.

rux

&&


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

A generally unsettled pattern remains for much of southern Alaska
for the beginning of the period as a large upper low sits over
the Bering. This feature looks to wobble around and slowly dive
southward through the end of the week. Moderate precipitation
continues across much of Southcentral on Thursday, heaviest along
the coast, gradually ending through Friday.

Models are in good agreement on the upper level pattern
amplifying as a shortwave and associated surface low swinging
around the base of the Bering upper low strengthens while moving
into the Gulf for the weekend. There are still differences in the
timing of this system, and consequently also the strength of the
ridge over Southcentral ahead of this system on Saturday, with the
GFS/GEFS being the strongest and most amplified solution.
Regardless, areas of moderate to locally heavy precipitation are
likely, especially along portions of the coast of Southcentral and
Alaska Peninsula this weekend. Scattered rain showers look to
remain across most of the Aleutians throughout the entire period.

-ME

&&
.AVIATION...

PANC...Gusty southeasterly winds out the Turnagain Arm are
expected to develop this afternoon/evening before abating some
overnight. Otherwise, expect VFR conditions to prevail throughout
the rest of the TAF period.

&&


$$