Flooding in Alaska, July 13 to 14, 2024

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
416 PM AKDT Sat Jul 13 2024

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

Southcentral remains downstream of a broad upper trough centered
over the eastern Bering this afternoon. Several shortwaves are
forecast to track through the base of the trough and across
Southcentral through tomorrow. The most notable of said troughs is
currently moving across Kodiak Island and into Cook Inlet.
Afternoon radar shows widespread showers lifting northward across
the Kenai Peninsula into the Susitna Valley and also Prince
Williams Sound. Afternoon observations show rain has also moved
into the Copper River Basin. Shower activity will continue to
spread across the region through tonight and into tomorrow. The
trough and its associated frontal system move inland on Sunday
with precipitation to taper off in coverage by midday. However,
precipitation is not expected to diminish entirely, as yet another
trough is forecast to track across Southcentral Sunday afternoon
and evening. This will result in renewed precipitation into Monday
night, especially across the Chugach Mountains and Prince William
Sound. Shower chances across Southcentral will persist until the
upper trough over the eastern Bering finally weakens and shifts
east of Southcentral.

Looking at observations across the region, it has been a
relatively cool day with areas remaining in the upper 50s to low
60s. Daytime high temperatures should change little into Sunday,
with Monday potentially seeing more widespread 60s, and even upper
60s possible across the Copper River Basin. Winds from Friday
have diminished substantially, though Turnagain Arm winds gusting
from 30 to 40 mph continue from Portage Valley to Bird Point along
the Seward Highway. Winds will gradually trend down through
tonight with a brief return of Turnagain Arm winds into Anchorage
tomorrow afternoon. Rainfall accumulations since midnight have
ranged from 0.10 inches to over 0.25 inches. Anchorage, Kenai, and
Talkeetna have hit or exceeded 0.35 inches with Willow up to 0.45
inches.

BL

&&

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

The forecast remains on track for the Southwestern mainland to
see continued unsettled weather over the short-term period.
Currently, a large Bering Sea low resides near the Kuskokwim
Delta. Numerous short-waves will continue to lift into the
mainland as this system meanders across the Yukon-Kuskokwim Delta
through Tuesday. Expect mostly cloudy, showery, and cool
conditions area-wide.

The pressure gradient between the slowly deepening eastern Bering
low and central Aleutians high pressure will cause a corridor of
westerly small-craft winds and higher wave heights to develop
across Bristol Bay and the 15 nm Bristol Bay marine zones. Wave
heights tonight through Sunday are expected to be on the order of
7 to 11 feet with the highest waves occurring Sunday. While the
westerly fetch is expected to continue into Monday, winds will
diminish Sunday evening and wave heights will also start to
subside by then as well. Similar conditions are expected for the
Pribilof Islands but mainly tonight through the first part of
Sunday before conditions slowly improve through Sunday afternoon
and evening. Additionally, the Pribilofs will also see light rain
at times through the weekend and into Monday as shortwaves
continue to rotate through on the backside of the Y-K Delta low.
Tuesday should be drier as high pressure begins to build in.

The Aleutian Chain should mainly remain dry over the next few
days. The only exception is for tonight into Sunday when a weak
North Pacific low straddles the Chain to the south. The western
and central Aleutians will have the best chance at seeing light
showers then. Showers taper off through Sunday afternoon as the
low continues to weak and move further south into the North
Pacific. A potentially stronger and more moist system could move
towards the western Aleutian Chain by Wednesday, but confidence
is low on the ultimate track, strength, and evolution of the
system at the moment.

&&

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

By the middle of the week, the upper level low (the same one
currently bringing widespread rain to Southern Alaska) will be
situated over Southwest and Southcentral Alaska. This low will
then slide slowly to the southeast into next weekend. An upper
level ridge looks increasingly likely to briefly build into
Southwest Alaska for the end of the week as well. What this means
for the weather is that, in general, there should be a drying
trend toward the end of next week.

Even by Wednesday the Kuskokwim Delta may have made the shift to
the rain ending while the Bristol Bay region of Southwest may
still see some showers before the low pulls southeastward. For the
latter half of the week most of Southwest Alaska should see
noticeable warmer and dryer conditions.

Southcentral will continue to see areas of rain on Wednesday. The
challenge for greater clearing across Southcentral is that while
the upper low itself moves into the eastern Gulf, the trough will
still extend northward toward the AlCan border for the second half
of the week. This will also usher in an elongated front to the
north Gulf Coast late Thursday or Friday. There may also be an
easterly wave or two that gets caught into the easterly upper
level flow that brings rain to the Copper River Basin. All these
possibilities with the upper level ridge remaining to the
southwest will make it more difficult for Southcentral to clear
out as well as Southwest. All that said, it bears watching to see
the details of this system as it tracks through the Gulf and see
whether it brings more showers in easterly waves or more clearing
than is currently expected.

&&

.AVIATION...

PANC...A series of fronts will move up Cook Inlet this afternoon
through Sunday evening and will bring in periods of IFR ceilings
in light to moderate rainfall. The first front is expected to
move through by early evening and and taper off the rain and turn
winds to the South and increase them as it does. Another period of
heavier rainfall and lower conditions may come through between
06Z and 12Z as a second front wraps around the low in the Bering
and moves into the area. Some improved conditions are expected
early Sunday morning into the early afternoon, but another wave
moves through late Sunday and may lower conditions to MVFR in
rainfall again at that time.

&&