Gale Warning 614, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
520 AM AKDT Sat Sep 14 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...

Main Points:

	- Widespread moderate rain and breezy/gusty winds this weekend.

	- Gusty southeast winds for the Hillside, south and west
   Anchorage starting this afternoon, becoming south overnight and
   continuing through Sunday throughout the Anchorage Bowl. Power
   outages due to saturated soils and wet vegetation are
   possible.

	- Exercise caution near rivers as forecasted river conditions are
   to be near bank-full for the Anchorage area and southern Mat-
   Su. A Flood Watch remains in effect for Anchorage small streams
   and urban areas through Sunday morning.

Active weather ensues for Southcentral Alaska this weekend with
breezy/gusty winds and widespread rain. A broad longwave trough
is currently over the Bering with a 120-140 kt jet streak
pointing towards the southern Mainland. The main surface low is
off of Nunivak Island with it's warm front beginning to push its
way over Kodiak Island this morning, shortly followed by the Kenai
Peninsula and most areas of Southcentral by the afternoon. Mostly
south to southwesterly winds at mountaintop level and
southeasterlies at the surface will mean all areas should receive
a healthy dose of rain by Sunday morning, with the only dryish
spot being from Eureka to Glennallen. Moving later in the day on
Sunday conditions will become more showery in nature as colder air
wraps into the system, focusing most of the precipitation on the
west and southwest facing mountain ranges. This will more or less
continue through Monday, but to lesser extent as time goes on.

The wind forecast, particularly for the Anchorage Bowl, is
perhaps the most challenging aspect of this forecast package. This
is due to the balancing act in the pressure field between the
much deeper low moving into the Norton Sound over the next 24
hours, progged at ~976 mb, and a low that will form at the triple
point this evening at ~996 mb. The pressure gradients are not
supportive for the Turnagain wind to bend into Anchorage until
late this evening, by which the Whittier to Anchorage gradient is
subsiding. However, all of the high resolution models bring a
Turnagain wind into town this afternoon, with gusts between 30 and
50 mph. This forecast package reflects a Turnagain wind that will
effect the hillside and the south and west portions of Anchorage
where strong winds will often mix their way north of the Turnagain
jet and form turbulent eddies.

Winds for the rest of the region are more certain with a coastal
ridge initially bringing in the typical gap winds this afternoon
and through early Sunday morning. By this time, 90% of the model
guidance has the Gulf low pushing inland, which will produce a
gusty up-Inlet wind that will extend north into the Susitna
Valley, as well as a reinforcement of the Copper Valley Wind. All
of this wind will be very slow to subside through Tuesday due to
the slow occlusion and movement of the primary low far to our
north. Tuesday looks to be somewhat of a break in the weather but
then another Bering low looks to generate up a rinse and repeat
scenario with more wind and rain on the way.

-CJ

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days
1 through 3)...

Forecast remains on track for a stronger front pushing over the
Southwest Coast this morning and then spreading across the rest of
the Southwest Alaska through the afternoon. Widespread rainfall of
up to an inch is possible for most areas through Sunday morning
as the front progresses eastward. An initial push of south-
southeasterly gale force winds move along the Kuskokwim Delta
coast this morning before weakening to small craft and
transitioning to southwesterly by this afternoon. Winds will
increase again overnight tonight to gale force before diminishing
again late Sunday morning. The Coastal Flood Advisory remains in
effect for communities along the Kuskokwim Delta coast from the
mouth of the Kuskokwim River to Newtok this morning through late
Sunday night to address minor storm surge concerns and expected
minor coastal flooding. Also, a River Flood Advisory has been
issued for communities along the lower Kuskokwim River from Bethel
to the mouth of the river through Sunday afternoon.

Attention then turns to developing storms in the North Pacific and
near Kamchatka that will look to merge as they approach the Bering
Sea. The gale- force low in the North Pacific looks to send its
front into the Western and Central Aleutians Monday. The storm
then moves into the southcentral Bering Monday afternoon where it
will merge with the Kamchatka system. The storm will continue to
deepen as it moves farther into the central Bering with the front
reaching the Eastern Aleutians and Pribilof Islands by Monday
night.

&&

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

Operational and ensemble guidance are in generally good agreement
with bringing a deepening upper low into the Bering late Monday
into Tuesday of next week. This low will be the focus for
potential impacts across Southwest and Southcentral Alaska during
the long term period. As the low overspreads the eastern Bering a
wet pattern with widespread showers is expected to persist from
Tuesday through at least Thursday from the Kuskokwim Delta coast
into Southcentral. At this time models are showing a deepening
trend with a robust front traversing the Aleutians and Bering into
interior Alaska. The thermal gradient along the front will favor
strong winds, even with the potential for some high winds through
the Eastern Aleutians into the AKPEN on Tuesday. The way the upper
low overspreads Southwest Alaska and then begins to meander
southeastward once finally undergoing some weakening by Wednesday,
suggests above normal shower chances will persist beneath the low
for much of both Southwest and Southcentral. Otherwise,
seasonably normal temperatures look probable through the period.

BL

&&

.AVIATION...

PANC...VFR conditions will persist through midday today as a front
from a system in the Bering moves over the area. Expect continuous
light to moderate rain through Sunday with MVFR ceilings and vis.
Vis may drop to IFR should heavy rain develop along the Turnagain
Arm convergence zone. Turnagain winds are likely with gusts up to
35 kts possible later this evening. Overnight winds will become
southerly and remain strong around 20 kts through the TAF period.

&&