Area Forecast Discussion
Issued by NWS Anchorage, AK

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558
FXAK68 PAFC 140045
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
445 PM AKDT Sun Jun 13 2021

.ANALYSIS AND UPPER LEVELS...

The upper levels feature a large upper level ridge extending
southwest to northeast across nearly all of mainland southern
Alaska this afternoon. A low and associated front are moving
across the northern Bering, and may bring some light rain and wind
to the Hooper Bay area this evening. meanwhile, a compact upper
low is spreading rain over the eastern Aleutians and into the
southern Bering south of the Pribilofs.

Extensive cloud cover has overspread the coast and Kuskokwim Delta
this afternoon, with a mix of sun and clouds with an extensive
Cumulus field developing for the Lower Kuskokwim Valley, and along
the Alaska Range. The clouds have grown upscale into towering
cumulus near Eureka, with partly cloudy conditions over much of
the rest of Southcentral. The morning fog and stratus has
dissipated along the coastal Kenai Peninsula, including Seward,
with some remnants remain over portions of Prince William Sound.
Once again most high temperatures today are in the 60s and 70s,
except 50s along the Bering coast where the cloud cover is
extensive.

&&

.MODEL DISCUSSION...

The models are in good agreement through Tuesday afternoon. The
main forecast challenges continue to be onset of sea breezes, high
temperatures, and afternoon minimum relative humidity values.
Forecast confidence is high.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Sunday night through Wed)...

Hot and dry conditions are expected over inland areas through
Tuesday as a ridge of high pressure remains parked over the
region. Expect high temperatures to push 80 degrees in parts of
the Mat-Su Valleys and Copper River Basin Monday with low 80s
possible on Tuesday. Coastal areas are unlikely to break 70 the
next two days due to strong sea breezes. Thunderstorm activity
will be limited due to strong subsidence aloft with only a slight
chance for a storm over the eastern Alaska Range.

Tuesday evening will begin a pattern change as a series of
easterly waves move in from the Panhandle/Southern Yukon Territory.
There is considerable uncertainty amongst the models with these
features, particularly the northern extent of the precipitation
field and shortwaves. Models often break down ridges too quickly,
so there`s a chance these waves may remain over the northern
Gulf. At this time the Prince William Sound and southern Kenai
Peninsula look the most likely to receive rain. With these
shortwaves there is always potential for convective activity over
the Copper River Basin and Talkeetna Mountains. However,
overrunning cloud cover prior to the arrival of the easterly waves
could limit instability from building throughout the day
Wednesday. Regardless, expect a pattern change towards overcast
skies and cooler temperatures on Wednesday. Southerly gap winds
are also likely to increase Wednesday as a coastal ridge builds
in.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 3...Tonight
through Wed afternoon)...

An upper level ridge will remain dominant across much of Southwest
Alaska, especially interior locations through Wednesday afternoon.
This will result in plenty of sunshine and warm temperatures.
Breezy conditions are expected Monday for much of Southwest with
winds southerly around 12-20 mph as the pressure gradient builds
across this area. This will be due to a frontal system
approaching from the Bering. These winds will diminish Monday
night though as the gradient weakens over the area. Temperatures
each afternoon will be a bit warmer with 60s and low to mid 70s
widespread. Some areas especially near Sleetmute Tuesday afternoon
and Wednesday afternoon may approach 77-80 degrees meaning summer
is in full swing.

For the Kuskokwim Delta, expecting this area to be more under the
influence of a frontal system approaching the area from the Bering
Monday. This frontal system is expected to bring coastal locations
of the Kuskokwim Delta periods of rain overnight through the day
Monday becoming more showery in nature after Monday afternoon.
Some of the rain may reach areas just west of Dillingham across
coastal Bristol Bay Monday morning/afternoon, though, not
expecting any rain to make it past Dillingham at this time.
Temperatures will remain cooler across the Kuskokwim Delta as a
result with 40s along the coast and 50s to possibly low 60s
inland. Tuesday night through Wednesday, the upper level ridge
builds over the Kuskokwim Delta leading to improving and warmer
conditions for Wednesday.

Lastly, an easterly wave is expected to cross the Alaska Range
Wednesday. As a result, there is the potential for increasing
showers and possible wet thunderstorms Wednesday afternoon. This
was left out for this forecast package though due to uncertainty
yet. Therefore, check back for subsequent updates.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 3...Tonight
through Wed afternoon)...

A low pressure system south of Adak currently will continue moving
northward into the Bering tonight. This low will phase with a
frontal system already present across the northern Bering. As a
result, moisture will stream north along it bringing rain and
unsettled conditions to the Pribilofs tonight through Monday
afternoon. The front that will bring rain to the Pribilofs will
undergo frontolysis (stretching apart of a front) Monday night.
However, a potent upper level low currently over the North
Pacific moves eastward tonight through Monday afternoon
reinvigorating the southern part of the front keeping areas
around Dutch Harbor unsettled through Wednesday. Winds will also
be gale force through the bays and passes along the eastern
Aleutian Chain as the front moves through tonight through Monday
evening.

Another piece of energy is expected to move into the western
Aleutian Islands overnight with rain and breezy conditions. This
system continues moving eastward through the Chain bringing
unsettled conditions to Adak and Atka Monday evening through
Tuesday night. This low will continue weakening as it moves into
the North Pacific Tuesday evening.

&&

.MARINE (Days 3 through 5: Wednesday through Friday)...

A well-developed low tracks south of the Aleutians through
Friday. Its front will bring gusty winds less than gale force over
the Central Aleutians increasing Thursday diminishing Friday.
Seas to 16 feet near the Central Aleutians building Thursday
subsiding Friday. A moderately strong and elongated North Pacific
Low remains nearly stationary through Friday. Its front spread
gusty winds less than gale force over the Gulf through Friday.

&&

.LONG TERM FORECAST (Days 3 through 7: Wednesday through Sunday)...

The long-term models have come into significantly better
agreement over the runs 24 hours ago. As usual, while details are
still highly in doubt, the timing and strength of the disturbances
causing active weather are in better agreement. Starting on
Wednesday, an inverted trough will make its way northwestward
across the Gulf, causing rain to develop over much of Southcentral
by Wednesday afternoon. Again, exact timing on that remains in
question. Meanwhile, quiet weather will persist over Southwest
Alaska and much of the Bering on Wednesday. A small and compact
low may produce some shower activity over the eastern Aleutians as
well. The gap winds will reintensify on Wednesday

On Thursday, the Southcentral disturbance will be over Southwest
Alaska, causing some shower activity there as Southcentral dries
out. The timing will depend on how fast that disturbance moves,
which there is some uncertainty about. The Bering will remain
generally quiet, with the usual widespread stratus and some shower
activity towards the western Bering.

By Friday a rex block pattern sets up with the large blocking
high over the northern half of the state and weak lows moving
across the Gulf and eastern Aleutians. The easterly flow should
bring somewhat cooler air in across the mainland.

For this weekend a stronger upper level low moves north out of
the Pacific towards the Bering, causing unsettled and wet weather
especially across Southwest Alaska. Depending on the strength and
track of the low, that wet weather could spread east into
Southcentral as well.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale 165 170.
FIRE WEATHER...NONE.

&&
$$

SYNOPSIS AND MODEL DISCUSSION...JPW
SOUTHCENTRAL ALASKA...CJ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MV
MARINE/LONG TERM...MK/JPW



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