992
FXAK68 PAFC 071327
AFDAFC

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

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

A large closed upper low centered overhead of the Eastern Aleutians
(Dutch Harbor) this morning serves as the anchor for a long-wave
trough over Alaska and the North Pacific. A few weak short-waves
embedded in the extremely large cyclonic flow around this low are
traversing Southcentral this morning, leading to some localized
areas of showers, most notable a line of persistent training
showers from Whittier to Portage and east Turnagain Arm. Partial
clearing has occurred over inland valleys. Temperatures have
cooled into the mid 30s to mid 40s, reflective of the cooler air
mass in place at the moment. Gap winds, which were quite strong on
Wednesday, have largely diminished, though the Turnagain Arm wind
into Anchorage International is lingering.

The most eye-catching feature in satellite imagery is a deep
vertically stacked low over the northeast Pacific (centered near
45N 146W as of 5am). The development of this low has resulted in
amplification of the flow in the NE Pacific with a ridge building
out ahead of it off the NW CONUS coast on up to the eastern Gulf
and SE Alaska. This in turn has led to a strengthening southerly
jet streak, which is helping to transport warm moist air north-
northwestward, well out ahead of the low. This atmospheric river
will head right for Kodiak later today and then continue westward
across the Alaska Peninsula into Bristol Bay, as it gets absorbed
into the flow around the Aleutian low. This is setting up to be
multiple days of moderate to heavy rainfall for Kodiak Island,
beginning later today and continuing through Sunday night.
This first storm looks the most impressive, with abundant
moisture, strong dynamical lift, and strong low level winds and
resultant upslope flow. As a result, Kodiak City and the east
side of the island will see particularly heavy rain tonight
through Saturday. There may then be a very brief break (where
rain will at least lighten up). However, a large cyclonic gyre
will take shape Saturday, with multiple strong short-waves/upper
lows rotating around the North-Central Pacific to the western
Gulf/Kodiak Island to the eastern Bering Sea and back south to
the Pacific. Thus, Kodiak can expect additional rounds of at
least moderate intensity rain. All of this will lead to potential
for flooding, which tends to happen on Kodiak with multiple days
of intense rainfall. Rainfall totals through Sunday night look to
be in the 3 to 6 inches range for the eastern side of Kodiak Island.

Meanwhile, the aforementioned upper level ridge will build
northwestward into Southcentral today, then strengthen over the
Yukon and AK Interior Saturday. This will lead to a warming trend
through Saturday, with interior Southcentral likely to see the
hottest temperatures of the summer thus far. While confidence is
high in significant subsidence from the ridge and rapidly warming
low level temperatures, the one wildcard will be the extent of
cloud cover on Saturday. The Gulf storm and strong upper level
short- wave will track westward to Bristol Bay, but the tail end
of the trough will lift northward toward Southcentral. This could
bring a fairly extensive cloud shield inland, which will have some
affect on high temperatures Saturday. In any case, rain will
spread to the Gulf coast/eastern Kenai Peninsula by Saturday
night. As the trough continues inland Saturday night, southeasterly
gap winds will rapidly increase - likely leading to a mild and
windy but dry night for much of the region. In the wake of the
trough passage, Sunday looks to be a bit cooler than Saturday for
Southcentral, but continued dry with gap winds likely persisting.

-SEB

&&


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

Unsettled weather will persist through the weekend as a broad,
upper-level low lingers near the Eastern Aleutians through
Saturday. By Saturday afternoon, the low merges with an
approaching low from the North Pacific and moves southeastwards
towards the Gulf of Alaska. Upper shortwaves will continue
rotating around the low through the weekend, driving weather
across the region. 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
easterly winds will persist across much of Southwest through
Sunday. For the Bering, expect northerly winds up to small craft.

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 this weekend
  for communities along Kuskokwim River.

* Minimum RH values dropping into the low 30s and mid 20s for the
  Middle Kuskokwim Valley and Western Alaska Range this weekend.

-AF/KC

&&

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

A couple of significant changes over the Alaska Weather Map
through Thursday. A Rex block builds from the Arctic into Mainland
Alaska through the period. This continues to support surface
thermal troughs over the Eastern Interior. One closed low wobbles
over the Gulf of Alaska and the Eastern North Pacific as it
weakens. A low center entering the Western Bering slips along the
Aleutians and merges with the Gulf low for Wednesday. With a ridge
forming over the Kamchatka and Chukotsk Peninsula, a third center
from the North Pacific with its front enters the pattern over the
Central Aleutians on Thursday. A blend of Canadian/ECMWF/GFS and
UKMET carries good confidence for the first half of the forecast,
with the EC and GFS straying from the group by the end of the
forecast.

The Gulf low aloft links up with a well developed surface system
for Monday and Tuesday. Locally heavy rainfall is expected across
coastal Southcentral Alaska, with the highest amounts along the
Eastern Kenai, Kodiak Island and parts of the Alaska Peninsula for
the beginning of the week. Gusty winds less than gale force will
occur along the North Gulf Coast, with gale force winds through
the Barren Islands and Shelikof Strait for Monday, diminishing
early Tuesday. Lesser amounts of rainfall moves inland to the
Alaska Range, and along the West Coast down to Bristol Bay. The
Aleutians and Bering will continue rain showers, with locally
gusty winds across the Central Aleutians through Tuesday. Another
area of gusty winds moves across the Pribilofs through Wednesday.
Another area of locally heavy rainfall comes in over the Western
and Central Aleutians with a low and its front late Wednesday into
Thursday, spreading East through the week.


-Kutz

&&

.AVIATION...

PANC...VFR conditions will persist. Turnagain Arm winds are
expected to bend back over the terminal by around noon again
tomorrow, then bend back away from the terminal by this evening.
Wind gusts tomorrow afternoon will not be nearly as intense as
they were yesterday, with peak gusts not expected to exceed 20 to
25 kts.

&&


$$