883
FXAK68 PAFC 180020
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
420 PM AKDT Wed Jul 17 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3: This
afternoon through Saturday evening)...

A potent short-wave, as seen on satellite this afternoon, will
continue to slowly dig southward through Thursday. In doing so,
showers will spread from north-to-south across the Susitna Valley
to the Kenai Peninsula. The timing for the steadiest rain to fall
around the Anchorage area is this evening/overnight into Thursday
morning before steady rain shifts southward over the Kenai
Peninsula. All rain/showery activity begins to taper off Thursday
late afternoon and evening as a pattern change gets underway.
Starting Friday, a change from cool and wet to warmer and drier
conditions will become apparent. High temperatures Friday will
range from the middle 60s to middle 70s with middle 60s to high
70s on Saturday. The coolest places will be around the coast where
sea-breezes ensue with the warmest locations in the Susitna Valley
and Copper River Basin. Any stray showers should remain in the
vicinity of terrain for Friday. There is a little more uncertainty
for Saturday with a series of easterly waves pivoting from the
eastern Gulf towards the northern Gulf coast. The best chance for
precipitation, if it occurs, would be for the communities along
the northern Gulf coast. However, showers, and perhaps a
thunderstorm or two, could be possible in the eastern Copper River
Basin depending on the exact track of the mesoscale shortwaves.

&&


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

A longwave trough descends over the southwest mainland and the
Eastern Bering Sea, while a longwave ridge develops across the
Aleutian Islands and the Western and Central Bering Sea. Embedded
shortwaves within the longwave feature will bring rain across
Southwest Alaska this afternoon, tapering off from west to east
late Thursday. With a robust upper low moving across the Western
Alaska Range, a slight chance for isolated thunderstorms remains
for this evening, although thermal instability looks poor,
especially with lingering cloud cover from the this morning`s
rain. As such, thunderstorm chances remain low. By Thursday, the
approaching ridge of high pressure will lead to warming
temperatures and the suppression of rain. Daytime highs climb
into the 60s and low 70s by Friday, with higher temperatures
likely over the weekend.

For the Bering Sea and Aleutian Islands, the building ridge will
likely lead to widespread fog and low stratus as moisture becomes
trapped near the surface. Fog is inherently difficult to forecast
and we forecasters tend to have a low bias (i.e. we under-do fog
coverage and severity). Therefore, be aware that fog may be more
widespread and thicker across the Bering Sea and Aleutian Islands
than is currently reflected in the forecast. By Thursday, an
occluding low moves in from the west, leading to windier and
wetter conditions. Forecast confidence is high that winds will
remain at or below small craft intensity. The front pushes
eastward through the remainder of the workweek, reaching the
Pribilof Islands by Friday night.


&&


.LONG TERM FORECAST (Days 4 through 7: Sunday through Wednesday)...

An omega pattern will dominate the long-term period, with large
upper-level lows situated in the Bering Sea and the North Pacific
near the Gulf. Between these lows, a high pressure ridge will
situate itself over Southwest Alaska. This setup will keep the
Bering Sea, Aleutian Chain, and southern Alaska Peninsula active
due to numerous shortwaves rotating around the Bering low. The
ridge, initially over Southwest Alaska Saturday and early Sunday,
will shift eastward toward Southcentral Alaska while weakening.
A frontal system is expected to approach Southwest Alaska Sunday
night as this ridge shifts eastward, with locally heavy rainfall
possible. Confidence remains relatively low in the front`s ability
to bring precipitation inland, but the coast is most likely to
see rain. Showery and unsettled conditions are expected across
Southwest Alaska on Tuesday as more shortwaves pass through the
Bering.

For Southcentral Alaska, the North Pacific/Gulf low will pull
easterly waves from the Yukon into the region. This pattern will
be favorable for precipitation in the Copper River Basin and the
Susitna Valley. As the ridge nudges westward from the Yukon,
temperatures across Southcentral are expected to rise to near to
above normal values. Afternoon thunderstorms are possible from
Saturday through Tuesday, although confidence in timing regarding
these easterly waves are very low at this time.

&&

.AVIATION...

PANC...A cold upper low just west of the Alaska Range in the
Kuskokwim Valley will drop into Cook Inlet tonight. Steady showers
will develop out ahead of it, tracking from the Kenai Peninsula
across Turnagain Arm to the terminal. This will lead to gradually
lowering ceilings late this afternoon through evening. Ultimately,
steady light rain will develop with MVFR conditions likely
settling in sometime between 06 and 12Z. There is a chance of
dropping as low as IFR sometime early Thursday morning, but it
would be fairly short-lived. Rain will taper to scattered showers
by late morning and low level flow will back from southerly to
easterly as the upper low exits southward toward Kodiak Island,
which should allow ceilings to lift. Offshore flow will develop
behind the low Thursday evening, ultimately leading to clearing
skies. Surface winds will remain light.

&&

$$