502
FXAK68 PAFC 181350
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
550 AM AKDT Wed Sep 18 2024

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

The strong low that tracked across the Bering Sea has crossed
into southern Cook Inlet early this morning. While not as strong
as it was earlier, it still is packing a punch with areas of heavy
rainfall and strong winds around it. This occluded low was
triple-wrapped by its front last evening as seen on satellite
imagery and these multiple waves will bring the periods of
enhanced rainfall today. There is a bit of cold air aloft
associated with this low center which is bringing in unstable air
with it. This instability kicked off a number of thunderstorms in
southwest Alaska yesterday, but it is marginal whether there will
be an isolated thunderstorm or two in Southcentral today as this
low passes through. Most likely areas will be right under the
upper low center as it tracks across southern Cook Inlet through
Prince William Sound. This low is continuing to move rather
quickly so it should move past the AlCan border this evening then
most of the precipitation should subside for Southcentral. However
there should be some stiff north to west winds behind the low
which will be strongest near the coast from Kodiak to Whittier.
One of the big questions will be whether these winds will be
enough to keep the lower atmosphere mixed enough after the
rainfall, or if all that moisture will result in widespread fog
tonight into Thursday.

The 12Z sounding this morning for Anchorage showed the freezing
level down to 4166 ft. Therefore expect the dusting of snow along
the higher peaks of the Chugach front range to hove turned into a
solid line of snow or elevations above 4000 ft when the some brief
breaks in the clouds develop late today and into tonight for
Anchorage and the Mat-Su.

In general, Thursday should see some breaks in the clouds for much
of SOuthcentral,with areas farther south such as Kodiak and Homer
seeing a good bit of sunshine. While there should be some sunny
breaks tomorrow for most o Southcentral, the wrench in it all is
that the longwave upper level trough really does not go
away. Another upper level short wave looks to dig into the
Susitna Valley Thursday night and stall over the Talkeetna
Mountains for Friday. This might result in the Copper River Basin
and Prince William Sound seeing some rain on Friday as a result of
this trough. With the cold air aloft, it is possible for some of
the mountain passes, mainly near Eureka and Paxson, to see snow
get close to the highway on Friday.

&&


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

Winds are continuing to gradually decrease as it shifts
northwesterly across Southwest Alaska and the eastern Bering Sea
this morning. Lingering showers will remain possible across
Southwest Alaska for today with likely chances near mountains and
the through the Kuskokwim Valley. Cooler air is expected to linger
through the rest of this week with widespread low temperatures
across Southwest Alaska hovering near freezing.

A ridge currently over the western Bering Sea will build toward
Southwest Alaska tonight. This should help to decrease chances for
precipitation for Thursday. Current satellite imagery under the
ridge indicates widespread low stratus across the Bering Sea and
most recent surface observations at Atka indicate that patchy fog
is developing as well. Looking ahead, there is low confidence for
how much extent this fog will develop across the Aleutians and the
Bering Sea. With light onshore flow and pressure building, it is
possible that the Kuskokwim Delta and Bethel could have patchy fog
for Thursday morning. While weak subsidence is likely for
Southwest Alaska, there is a low potential for embedded shortwaves
to bring brief periods of precipitation (rain, snow, or a mix) to
Southwest Alaska Friday and this weekend. This should be very
minor and not widespread.

Farther west, a front accompanying a Kamchatka low is expected to
move into the western Aleutians this afternoon. The ridge will
help slow the fronts progression, keeping rain chances likely for
the western Aleutians. This feature is expect to interact with a
North Pacific low approaching the western Aleutians and could be
the vehicle to help spread precipitation east and a track for
additional troughs. With a strong ridge in place, the trough is
expected to be somewhat deflected to the east and track light
showery activity along the Aleutians to the Alaska Peninsula
through Friday. Meanwhile, as the Kamchatka low lingers, another
low will quickly follow into the western Aleutians for Thursday
night, though model agreement begins to fall apart for the low
trajectory and how it interacts with other synoptic features for
Friday and this weekend. Models hint at continued troughing for
the Aleutians, while high pressure sits in the northern Bering
Sea.

rux

&&


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

Latest operational models show little agreement by Friday, so
will lean more on the ensemble means for the long term forecast. A
broad upper low positioned over the Western Aleutians looks to
slide eastward into the western Gulf by Tuesday. Upper-level jet
support should remain on the south side of the low with the
strongest winds at the surface to remain largely south of the
Aleutians. This looks to promote a quieter period of weather for
both the Bering, Southwest Alaska, and Southcentral Alaska through
the weekend. Instead, drier and cooler conditions are forecast
and lowering snow levels as a cooler airmass slowly makes its way
from interior Alaska into Southwest Alaska by Tuesday. As the low
becomes anchored over the western Gulf early next week, some
potential will exist for the return of shower chances for
Southcentral as easterly waves may bring scattered showers to the
Copper River Basin, Prince William Sound, and Gulf coastal
regions.

-BL

&&

.AVIATION...

PANC...MVFR to IFR ceilings and light rain are expected through
Wednesday afternoon, then VFR conditions return Wednesday night
into Thursday. There is a chance for some fog Wednesday night if
the winds become light and clouds clear out significantly.

&&


$$