068
FXAK68 PAFC 081353
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
553 AM AKDT Sat Jun 8 2024

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

Key Messages:

1) A Flood Watch remains in effect for Kodiak Island through late
Sunday night. The forecast remains on track for periods of moderate
to heavy rain, with 3 to 6 inches of rainfall expected along the
east side of Kodiak Island. The heaviest rain will be during the
day today and then during the day on Sunday. Urban and small
stream flooding are possible. Landslides are also possible in
areas of steep terrain.

2) Interior Southcentral from the Mat-Su to the Copper River Basin
will see some of the warmest temperatures of the summer this
afternoon, with widespread 70s. Temperatures will then trend
cooler Sunday through Monday, though dry conditions will prevail
for most of the region.

3) A major storm system approaching the Gulf of Alaska today will
bring high winds and waves to most of the Gulf coastal waters.
Strong gusty winds will also spread inland this afternoon and
evening, with particularly strong winds through Portage Valley
and Turnagain Arm. Travelers should use caution if driving
through these areas.

A look at satellite imagery this morning shows a vertically stacked
low approaching the southern Gulf of Alaska, with an atmospheric
river tracking up the east side of the low then westward toward
Kodiak Island. Moderate rain has been falling in Kodiak City for
much of the night, with over three quarters of an inch of rainfall
recorded thus far. Strong winds have developed across much of the
Kodiak Island waters, with surface observations and satellite
winds overnight indicating 25 to 35 kts over most of the area.
Winds are beginning to strengthen along the north Gulf coast and
into Cook Inlet this morning as the entire storm system shifts
northward. Meanwhile, a high amplitude ridge extends from British
Columbia to the Alaska Interior, with the ridge covering much of
Southcentral this morning. High clouds are tracking up the west
side of the ridge and cover all of Southcentral. Temperatures
across the region range from the mid 30s to mid 40s.

The forecast is very much on track for what will be a hazardous
weather day across much of the region today. A subtle change is
that the approaching Pacific storm and upper trough are further
north than models had advertised the past few days. As a result,
the upper ridge is also further north and will have less influence
on Southcentral`s weather today. The result of this is more
clouds over Southcentral, slightly cooler temperatures (though
still quite warm over interior Southcentral), and a faster arrival
of rainfall along the north Gulf coast and eastern Kenai Peninsula
later today. What hasn`t changed is that Kodiak Island remains
the focal point for the heaviest rainfall this weekend.

One notable change to the forecast with updates made last evening
and early this morning is to up some of the gap winds this
afternoon and evening. The general ingredients for strong and
gusty winds remain the same: the low and surface front weakening
as they track westward across the Gulf and toward the Alaska
Peninsula; high pressure building in behind the low and surging
northward into Southcentral leading to pressure rises; the tail
end of a strong upper level short-wave lifting northward across
Southcentral; and steep low level lapse rates due to warm surface
temperatures. The aspects that look more impressive than in prior
days include the overall strength of the low level flow over
Southcentral and the lapse rates in the lower atmosphere (many
forecast soundings show 5000 feet or more of dry adiabatic lapse
rates starting from the surface). The reason for both of these is
likely the further north position of the trough and ridge, with
cooler temperatures aloft moving in from the Gulf coincident with
the pressure rises. Bottom line, there is good potential for some
unusually strong winds and in some locations out of an unusual
direction. The prevailing low level flow will be easterly and
gusty easterly winds could mix down to the surface for many
coastal locations including Cordova, Valdez, Seward and most of
the Kenai Peninsula. Seward is the most interesting because strong
easterly winds are not common. Some of the strongest winds will be
through the typical gaps, including Portage Valley, Turnagain Arm,
and the Knik River Valley. A Special Weather Statement has been
issued to highlight the strong winds through Portage Valley and
Turnagain Arm, which can be particularly hazardous to high profile
vehicles such as RVs and fishing boats on trailers.

Once the winds move into Southcentral this afternoon and evening,
they will tend to linger into the overnight hours. This means
temperatures will remain more elevated tonight than normal. Sunday
will see a weaker repeat of today, with a new low tracking south
of Kodiak, sending another front northward across the Gulf. This
will lead to the second round of moderate to heavy rain for Kodiak
Island. The front will weaken as it nears the north Gulf coast,
but bring another round of rain to coastal Southcentral Sunday
night. Inland portions of Southcentral will remain dry, with some
breaks of sun. However, with cyclonic flow firmly in place aloft,
expect marginally cooler temperatures. Gap winds will also
redevelop during the day Sunday as a coastal ridge strengthens
ahead of the approaching front. Winds will not be as nearly strong
or widespread as they will be later today.

Looking to the new work week, low pressure will continue to spin
south of Kodiak. However, features will be weaker both at the
surface and aloft, so rainfall for Kodiak will be much lighter.
There are hints of some weak upper level short-waves moving into
Southcentral from the east, however model agreement is poor. The
NAM/GFS are beginning to hint at a more significant "easterly
wave" Monday night into Tuesday, which would bring a return to
rain and cooler temperatures for Southcentral. Stay tuned as we
continue to monitor this potential.

&&


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

Overall, the forecast remains largely unchanged since the
previous forecast package. Unsettled weather will persist through
the weekend and Monday as a broad, upper level low currently in
between Adak and Unalaska merges with several other upper level
features approaching from the North Pacific. As the resulting
broad low slides southeastwards towards Kodiak Island, several
upper level shortwaves rotating around the low will promote wet
and windy conditions over much of the area through Sunday and into
Monday. Thus, the general expectation is for coastal Southwest to
see cloudier and wetter conditions, whereas interior Southwest
will have warmer and drier conditions. Gusty east to southeasterly
winds will persist across much of Southwest through Monday, as
well. For the Bering, expect northerly winds up to small craft.
Despite some minor model differences with respect to the exact
details of the forecast, here are some aspects we can say with
higher confidence:

* Precipitation intensity will remain fairly light for
  communities not on the Pacific side of the Alaska Peninsula.

* Several rounds of gusty east to southeast winds, with gusts as
  high as 40-50 mph, for interior Bristol Bay through the weekend.
  Highest gusts are expected on Sunday. This morning, Bristol Bay
  itself can also expect small crafts with gusts up to 40 mph and
  seas up to 9 feet.

* Daytime highs climb into the high 60s and low 70s (and relative
  humidity dropping into the high 20s and lows 30s) this weekend
  for communities along Kuskokwim River.

-AF/KC

&&

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

The upper level low over the Gulf of Alaska/Eastern North Pacific
continues its oscillations and weakens through the forecast
period. Several troughs rotate along the Southcentral Coast
through the end of the workweek. The Arctic high builds over the
Mainland and ridges towards Southwest Alaska. Developments with
this high bear further watching to check the displacement of the
transient systems. A Western Bering low diverts to the Russian
Arctic, while a North Pacific low works its way across the
Aleutians into the Bering by Friday. Good agreement in the model
guidance, with the ECMWF making some deviations towards the end of
the period.

Periods of rain will continue over Southcentral Alaska, and as
far North as the Alaska Range through Friday. A longer term
rainfall event with locally heavier rain is possible from the
Southern Kenai Peninsula across Kodiak Island into the Alaska
Peninsula through Thursday. Showers over Southwest Alaska, AKPEN,
the Eastern Aleutians and the Pribilofs occur through the period.
Locally heavy rain associated with the North Pacific low and front
spreads across the Western and Central Aleutians late Wednesday
through Friday. Gusty winds approaching gale force with the front
as it moves over the Aleutians Thursday through Friday.

-Kutz

&&

.AVIATION...

PANC...VFR conditions are expected to persist. A very challenging
wind forecast is setting up for this afternoon into tonight, with
a broad range of scenarios ranging from strong, gusty southeast
wind at times to calm northerly wind at the surface with low
level wind shear at the terminal. At this time, it appears likely
there will be a short window for the pressure gradient between
Anchorage and the Susitna Valley to be strong enough to briefly
overcome a strong down-inlet pressure gradient developing out
ahead of a strong trough moving into the Kenai Peninsula from the
northern Gulf. Southeast gusts associated with a strong Turnagain
Arm wind clipping west Anchorage as strong as 35 kts will be
possible for a brief time, most likely between about 2z and 6z
tonight. Winds will likely then bend away from the terminal
briefly, but will return in a weaker state later on Sunday morning
after the trough passes through and lifts north.

&&


$$