285
FXAK68 PAFC 121300
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
500 AM AKDT Sun May 12 2024

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

A weak low and associated occluded front are dissipating along the
North Gulf Coast and Prince William Sound areas this morning, with
steady precipitation transitioning to showers. Multiple weak
short-waves rounding the upper low center are producing isolated
showers inland from the coastal mountains. A short-wave which
ejected out of the long-wave trough yesterday has formed a low
over the eastern Interior near the ALCAN border. This has been
producing steady light precipitation along portions of the Tok
Cutoff from around Slana to Mentasta Pass. Webcams show some
fresh snow accumulation through Mentasta Pass, but the snow has
not stuck to the roadway. This precipitation is tapering off early
this morning as the low drifts northward. With extensive cloud
cover across the region, temperatures have held to a narrow range,
but have slowly dropped into the 30s for most locations.

The upper level low will open into a trough and exit to the Yukon
later today. In it`s wake, weak vorticity maxima will rotate
around a short-wave ridge centered over interior Southcentral
northward across the Alaska Range to the Alaska Interior. Weak
upper level forcing combined with increasing breaks of sunshine
and weak instability will produce isolated to scattered showers
across the region. Meanwhile, a weak low and short-wave south of
the eastern Aleutians this morning will track quickly along the
base of the long-wave trough into the Gulf tonight. This will
bring a quick shot of rain to Kodiak Island, mainly the east side
of the island. The low will remain offshore as it continues across
the Gulf on Monday, with little or no precipitation reaching the
north Gulf coast.

The big story for Monday and Tuesday will be increasing amounts
of sunshine and warmer and drier conditions. a couple distinct
short-waves will track across interior Southwest Alaska Monday,
but then quickly weaken as they reach Southcentral due to
increasing anticyclonic flow along the front edge of an amplifying
ridge (ahead of a deep low crossing the the Bering Sea). There
could still be some diurnally driven showers near the mountains,
but expect the bulk of the region to be dry.

-SEB

&&


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

A weak, elongated low is moving south of the central and eastern
Aleutian Chain this morning, producing areas of light rain and
east to northeast small craft winds moving quickly east along the
Chain. This low will skirt south of the AKpen later today,
allowing quieter conditions and northerly flow to spread into most
of the Bering Sea and Aleutians as a strong upper ridge builds
into place behind this low. Across Southwest, there will be
lingering influence from a decaying low now situated over the Gulf
of Alaska as a messy upper trough continues to drift overhead.

By this afternoon, breaks in cloud cover already showing up on
satellite this morning should allow for enough heating and low
level destabilization for scattered showers to develop across much
of the Lower Kuskokwim Valley and Bristol Bay. The lingering
question is whether any of this can become deeply developed enough
to produce any lightning, as forecast soundings still show a
relatively warm, dry layer in the mid to upper levels that could
keep showers rather low-topped today. There will be a couple weak
upper perturbations rotating around the Gulf low into Southwest
today, and this could be the tipping point providing enough lift
to cool the upper levels and assist in allowing for a few
thunderstorms developing along the Alaska Range, perhaps drifting
out into the Lower Kuskokwim Valley before dissipating with loss
of daytime heating later tonight. Additional rounds of showers
will be possible on Monday, mainly near the Alaska Range out ahead
of a shortwave trough digging south around the developing Bering
ridge. However, instability looks even more marginal on Monday,
and thunderstorms are unlikely.

Attention from there shifts to a much stronger system poised to
affect a large portion of the outlook area later in the week. By
Monday, a strong 970s-980s mb low moving off of Kamchatka will
extend a warm front into the western Aleutians, with southerly
winds picking up into gale force range along and behind the
initial front across the western Aleutians and Bering A cold front
will move in quickly behind the warm front and begin to occlude
it on Tuesday morning, while the parent low moves farther into the
far northern Bering Sea. High-end gale force southerly winds will
spread east towards the central Aleutians and Pribilofs, while
winds remain strong but turn westerly behind the cold front. Bands
of light rain following both frontal features should also shift
from the western Aleutians to the central Aleutians and past the
Pribilofs on Tuesday.

By Tuesday night, the main low and trailing front will begin to
weaken as the low center moves up towards St Lawrence Island.
Even so, guidance is beginning to show the wind field holding on
for longer, and there is potential for 30 to 40 mph southerly
winds to reach the Southwest coast as early as Tuesday afternoon,
especially near the Kuskokwim Delta. It is too early at this time
to determine exact potential for higher than normal water levels
moving in with this system. However, coastal communities across
the Kuskokwim Delta should continue to monitor the forecast for
updates over the next couple days while we continue to follow this
strong spring low pressure system.

&&

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

For Southcentral...

By the long term, south central will be dried out and slowly
warming with conditions returning to, or exceeding normal.
Ridging over much of the mainland will persist through the end
of the week. Clouds will be intermittent across region but some
afternoon showers will develop across the Wrangell mountains.
By the weekend, clouds and rain will return. A low pressure
system will drop down from the northern Bering, south across
southwest Alaska and into the Kodiak/Western Gulf of Alaska.
Present forecast guidance keeps this system only precipitating
on Gulf communities, though there is a chance the system will
shift north, bringing wider spreading rains to the mainland.
Overall, temperatures will continue to rise, with daytime highs
warming (with no snow).

For Southwest and the Bering/Aleutians...

The first of two systems will move across the Bering Wednesday
and Thursday. This system will drag a front across the Aleutian
chain, bringing winds, rain and shifty winds will follow as this
tracks east. The brunt of the winds, outside of the Bering, will
be be focused towards Bethel into Wednesday evening. The next
weather system will develop across the western Bering and move
along the Aleutian chain. It is still too early to pin down
specifics on the movement of this low a week out, but trends are
sliding it south of Bristol Bay by the weekend.

&&

.AVIATION...

PANC...VFR conditions will prevail through the TAF period. Light
slight southwesterly winds this morning will give way to gusty
southeasterly winds out of Turnagain Arm late this afternoon.
These winds will bend into the terminal with pressure gradients
becoming favorable as a low pressure system passes south of Kodiak
and re-orients the coastal ridge to the favorable east-to-west
direction. Unlike an instability driven Turnagain Arm wind bending
over the terminal with day-time heating, this will be mostly
pressure gradient driven with southeast winds peaking this
evening. Winds turn light and out of the north Monday morning.

&&

$$