413
FXAK68 PAFC 240146
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
446 PM AKST Sat Nov 23 2024

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

Calmer conditions are expected from tonight through tomorrow
morning as winds diminish. While no precipitation is expected,
cloud cover will increase ahead of a low advancing from the Bering
Sea. As this low and its front move in, expect a round of snow
from Sunday afternoon through Monday, followed by a downward trend
in temperatures from Monday night through Tuesday.

Snow will likely be the most impactful aspect of this forecast.
There remains some uncertainty with snow amounts, especially as
models continue to shift with timing and precipitation amounts.
Confidence is high that the greatest snow amounts will occur along
the western slopes of the Talkeetna and Wrangell St. Elias
Mountains due to favored upsloping from westerly flow. About 5-6
inches of snow are forecast along the Parks Highway from about
Willow north, while lower amounts (3-4 inches) are expected from
about Glennallen north in the Copper River Basin. For Mat Valley,
Anchorage, Turnagain Arm, and Valdez, up to about 3 inches. Snow
amounts could be a bit higher than currently forecast, but the
quick movement of the front into and out of Southcentral means
that this won`t be a prolonged snow event and, therefore, snow
amounts should remain on the lower end.

Another aspect of the forecast that is subject to lower confidence
is the chance for dense fog to develop again along Cook Inlet and
the Knik Arm. The presence of fog this morning increases the
confidence that fog will redevelop tomorrow morning, especially as
the temperature inversion will not have had a chance to fully
reverse. Still, confidence is low on exactly where and when fog
will form. Incoming clouds will also make fog difficult to monitor
via satellite.

-Chen

&&


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

The leading edge of a front associated with a vertically stacked
Bering low continues to move over portions of Southwest Alaska
this afternoon, especially over the Kuskokwim River Delta. With
high pressure settled in over the mainland, a significant
temperature inversion has been in place for most of Southwest.
This inversion has weakened some with warm air filtering in at the
surface as the front moves over, limiting the freezing rain risk
to this point. Areas around Aniak that will remain sheltered from
the wind could experience brief periods of freezing rain during
the morning and early afternoon hours on Sunday.

By Sunday evening and throughout the day Monday, the front will
move eastward towards the Alaska Range, producing light to
moderate snowfall as it shifts towards Southcentral. For Bristol
Bay, a mix of rain and snow will be experienced as the front
passes over Sunday-Monday. Behind the front will be another push
of cold air advection that will again trend temperatures down as
the week progresses. The biggest temperature shift will occur on
Tuesday as far interior portions of Southwest could once again
fall below zero degrees. For the Bering and Aleutians, a shortwave
trough will retrograde to the north and west starting Monday
morning and continuing through Tuesday afternoon. Gale force winds
and moderate precipitation will be felt along the western Bering
and Aleutians as an area of high pressure currently over eastern
Russia builds over the central Bering and extends towards the
mainland by the end of the forecast period, limiting any chances
of precipitation for the rest of the forecast area.

-BS

&&

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

Significant weather changes are expected over Alaska throughout
the long term period, with evolving dynamics in the North Pacific.
The period begins with a ridge of high pressure over the Bering
Sea and a positively tilted trough digging over eastern Alaska and
the Yukon. A large upper-level low over the North Pacific is the
key player, but models differ in its progression. The GFS
indicates the trough will deepen, allowing the North Pacific low
and additional shortwaves to move northeastward, spreading more
widespread precipitation across the region, particularly along
the coast. In contrast, the ECMWF suggests the initial trough
evolves into an upper-level low over mainland Alaska, shunting the
North Pacific low southward and leaving much of Southwest Alaska
and parts of Southcentral Alaska drier during the period.

Regardless, gale-force winds are expected to continue over the
Bering Sea early in the period. Snow is also expected to spread
across Interior Alaska by Wednesday, reaching near the
Southcentral coast with coastal areas east of Prince William Sound
potentially seeing a mix of rain and snow. Depending on how the
North Pacific low progresses, as suggested by the GFS and other
guidance, moderate rain and snow could develop near the eastern
Aleutians and AKPEN by Friday and potentially spreading towards
Kodiak Island and the Southcentral coast by the end of the period.
However, with model disagreement, there remains uncertainty in
the exact timing and extent of precipitation, though there is a
strong signal for impacts at some point.

Eovino

&&

.AVIATION...

PANC...VFR conditions and light winds will persist through this
evening. There will be a chance for fog and/or low stratus to
develop once again late this evening into tonight and potentially
affect the terminal with IFR to LIFR conditions at times. There is
still fairly low confidence regarding whether or when fog could
redevelop along the Cook Inlet and Knik Arm and how easily it
could clear out on Sunday morning. A weak southeast wind
developing through the Turnagain Arm could reach the terminal as
well, but will likely hold off until late in the afternoon on
Sunday at the earliest.

&&
$$