617
FXAK68 PAFC 080100
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
500 PM AKDT Fri Jun 7 2024

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

A longwave trough in the North Pacific continues to slowly move
northward towards the southern Gulf of Alaska. Weak waves from
this trough are passing over the western portion of the forecast
area along the Alaska Range and Kenai Mountains, producing a few
isolated showers through this evening. With a ridge starting to build
in over the interior, clearing has taken place over much of the
Copper River Basin. Most of the gap winds have subsided with the
exception of the Turnagain Arm wind by West Anchorage and the
International Airport.

As the ridge extending from the NW CONUS up to SE Alaska continues
to build in, southeasterly flow will help move warm moist air
northwestward towards Kodiak Island. Light rain has already
started on the island but will quickly pick up in intensity over
the course of the forecast period. The first round of
precipitation for Kodiak Island will go on through Saturday night,
before the low moves into Bristol Bay. Strong upslope flow,
abundant moisture, and dynamic lift will all be factors in strong
rainfall over the island. An additional low will enter the
western Gulf Sunday morning and provide another round of
precipitation that will currently last into Monday. Similar to
the first system, ample moisture, lift, and upslope flow will
again aid the intensity of precipitation over the island. As a
result of the timing and intensity of these storms, a Flood Watch
was issued for Kodiak Island starting tonight and going through
Sunday night, with the potential for 3 to 6 inches of rainfall.
While rain will last into Monday evening, the intensity will
quickly diminish after the morning hours.

As this is taking place, the ridge over SE Alaska continues to
build in over the weekend. This will help create a warming trend
for all of Southcentral on Saturday, likely resulting in the
hottest day for most locations this year. The one challenge with
the temperature forecast for tomorrow will be the amount of cloud
cover over the region due to the trough in the gulf. In addition
to the trough producing heavy rainfall over Kodiak Island,
multiple waves of precipitation will move over the Kenai
Peninsula and Prince William Sound starting Saturday night and
continuing through Monday afternoon. A frontal passage form the
trough on Saturday night will also support the rapid development
of gap winds, with the strongest winds lasting through Sunday
morning. This will result in mild and windy, but mainly dry
conditions for much of the area. As the front passes, cooler air
will move in over Southcentral and remain through the early part
of next week.

-BS

&&


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

Unsettled weather will persist through the weekend as a broad,
upper level low currently near 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. 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. For
the Bering, expect northerly winds up to small craft. The overall
weather picture remains largely unchanged since yesterday, but the
details remain in flux as models work to resolve weak upper level
shortwaves moving around the low.

Here are the hazards/notable weather currently being monitored:

* Periods of moderate to heavy rain (with storm totals hovering
  around 0.5 to 1 inch) likely on the Pacific side of the Alaska
  Peninsula as several waves of precipitation move in through the
  weekend.

* Several rounds of gusty east-to-southeast winds, with gusts as
  high as 40-50 mph, for interior Bristol Bay through the weekend.

* 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.

Let`s talk a bit about uncertainty. Forecast confidence remains a
bit lower in the exact details. This is due to model disagreement
with the numerous shortwaves rotating around the upper low, which
in turn affects where the associated surface lows move and
evolve. In a pattern like this, dominated by a fair amount of
upper level energy moving and interacting in a chaotic manner,
it`s quite possible the details of the forecast will shift in
future updates. Some aspects of the forecast we can say with
higher confidence: precipitation intensity will remain fairly
light for communities not on the Pacific side of the Alaska
Peninsula, and Southwest Alaska can expect to see several rounds
of winds, with the strongest arriving Sunday with gusts up to
40-50 mph. Exact rain amounts and wind gusts will be the details
we`ll work to hone in on with future forecast packages.

-KC/AF

&&
.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 to continue through Saturday. Turnagain Arm
winds bending into the terminal this afternoon will diminish
later this evening, though are not expected to exceed 20 knots.
Into Saturday weak northerly winds prevail through the afternoon
hours.

&&


$$