365
FXAK68 PAFC 161248
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
448 AM AKDT Mon Sep 16 2024

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

A shortwave trough is moving across Southcentral and the Gulf
this morning. Isolated to scattered showers are continuing across
the northern Susitna Valley, eastern Prince William Sound, and the
mountains along the Chugach and the Talkeetna. Gusty winds
through Kenai and Anchorage from southwesterly flow up Cook Inlet
should start to decrease this afternoon along with the showery
activity. The exception to this will be along the Alaska Range and
the Wrangells north of Gakona. Precipitation will likely linger
until early Tuesday morning for those locations as a central low
passes through the central Interior of the state and a weak
shortwave dips slightly into the Susitna Valley and Copper River
Basin. A brief weak ridge will help to clear some skies later
tonight as the next front reaches the western Gulf and Kodiak
Island.

Cloud cover will become more important tonight into Tuesday
morning as cooler, drier air filters into Southcentral. For areas
that clear, light winds and weak ridging will allow for good
radiational cooling overnight and Tuesday morning temperatures may
feel a bit chilly as temperatures drop into the 30s to lower 40s
for most areas in Southcentral. The Copper River Basin will likely
see the coldest morning temperatures will lows looking to bottom
out in the low 30s. Patchy valley fog and patchy Cook Inlet fog is
possible for some of the locations that manage to clear.
Increasing mid and upper level cloud cover, moving in from the
south, should keep temperatures from dropping too low for areas
along the Cook Inlet up through the Mat-Su Valley, but timing of
this will factor heavily into how low temperatures drop. One thing
to note, is that we are now reaching that time of year when we
start seeing our first temperatures of 32 degrees for the upcoming
cold season. Now is a good time to start thinking about how to
protect those cherished warm season plants that are still outside
as we start to increase our chances reaching low temperatures of
32 degrees or lower.

The next system will be another wet one with south to
southeasterly flow for Southcentral Tuesday and Wednesday. Winds
could be gusty through the Copper River and Turnagain Arm. The
front will spread across the Kenai Peninsula late Tuesday morning,
then to Anchorage, Prince William Sound, the Matanuska and
Susitna Valleys in the early afternoon. Rainfall intensity will
increase Tuesday night into Wednesday for eastern Prince William
Sound. Precipitation will gradually diminish for much of
Southcentral later Wednesday as the low starts to move across the
northern Gulf. Thursday looks to be a little bit quieter, with
light showers lingering around the mountains. Overall,
temperatures will remain on the cooler side through the rest of
the week.

- PP / rux

&&


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

Forecast remains on track for a stronger system to move into the
Bering Sea this afternoon and trek eastward towards Southwest
Alaska through Tuesday. Models are slow to agree on the track for
this system and some uncertainty remains. There has been a
gradual southerly trend, pushing somewhere onshore into Greater
Bristol Bay. The current forecast leans toward the EC and
Canadian, which are reasonably aligned. The GFS, however,
continues to be the southern outlier, though consistently
southern. The NAM is more of a middle ground solution but does
ultimately trend closest to the GFS. There is better agreement on
higher winds pushing into Bristol Bay, with gusts to storm force
likely, and waves reaching 13 to 17 ft. Questions that need to be
resolved, however, are the placement of the low and duration of
winds. A further north and deeper solution of the low would extend
the duration of winds into Bristol Bay and possibly necessitate
some flood products. A more southerly track, such as the GFS
solution, would still bring very strong winds into Bristol Bay,
but for a shorter duration as the GFS solution is more progressive
with the low.

As low as it occludes, it does so in a bent-back fashion, pulling
colder, northerly air along the backside and increasing winds to
storm force. There is decent agreement for the Pribilof Islands to
be impacted by these storm force winds Tuesday afternoon. Saint
George has the greatest chance for strongest winds.

&&


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

By the start of Thursday morning a building ridge over the
eastern Bering Sea appears to settle in. The resiliency of ridges
is usually a point of contention in the model solutions, however
agreement is currently strong regarding a fairly strong ridge
remaining over the area, warding several low pressure systems off
south of the Chain into the early portions of the weekend. Model
uncertainty is much higher to the east in Southcentral and the
Gulf of Alaska. By Friday morning, the GFS solution pulls a fairly
strong low pressure system up from the northern Pacific into the
Central Gulf, spreading wind and rain across the coast, whereas
the Euro and Canadian models keep a mild trough in the northern
Pacific, with Southcentral staying clear. By Sunday morning,
solutions comes back into better agreement with the ridging over
the eastern Bering weakening as a strong low pressure system fills
over the western Aleutians and a new low over the the Gulf of
Alaska. A broad troughing pattern looks to resume thereafter,
which will keep shower chances in play for both Southwest and
Southcentral Alaska through the remainder of the long term period.

-CL

&&


.AVIATION...

PANC...VFR conditions persist. Southerly winds around 25 to 35
kts this morning will remain gusty but gradually diminish through
today. Isolated to scattered showers move through this morning
but should be mostly focused along the Chugach Front Range, away
from the terminal. From this afternoon through Tuesday morning,
high confidence in a spell of fairer conditions with no rain,
lighter winds, and VFR conditions expected. The is a small
possibility for patchy fog after midnight into Tuesday morning if
skies clear and overnight temperatures cool. Later on Tuesday, a
front will bring a return of rain and stronger winds.

&&


$$