Flooding in Alaska, August 7 to 8, 2024

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
424 PM AKDT Wed Aug 7 2024

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

New and updated flood products are in effect as we continue to
monitor the impacts of widespread rain across Southcentral Alaska.
To summarize:

- A Flood Warning is in effect for the Seward area through Friday
  afternoon.
- A Flood Advisory is in effect for the Yentna and Lower Skwentna
  Rivers until Saturday afternoon.
- A Flood Watch remains in effect for Eastern Kenai Peninsula
  through Thursday afternoon.

With rain continuing across the Southern Mainland through
Thursday, please exercise caution if you live near (or will be
around) rivers, streams, and other bodies of water. Rain could
also lead to ponding on roads, so use caution while traveling.

Diving into the details... an atmospheric river continues to
impact Southcentral Alaska, with the worst of today's rainfall
occurring along the Eastern Kenai Peninsula coastline. As an upper
level shortwave moves in early tomorrow morning, models are
trending towards the development of a weak triple point low in the
north Gulf coast near Kenai Peninsula. With this new development,
have increased rain amounts along the rail belt as rain wraps
back around from the north. Forecast confidence is on the lower
side regarding where exactly this wraparound will occur, leading
to uncertainty in rain amounts. As the atmospheric river gradually
pivots eastward from now until Thursday night, expect the
heaviest rain to shift towards Eastern Prince William Sound,
including Valdez and Cordova. Overall, many areas will see around
an inch or more of rain before the atmospheric river moves east
and out of the area.

A weak, transient ridge builds in behind the departing atmospheric
river, leading to a short spell of quieter weather for Friday.
Expect skies to remain cloudy, with isolated to scattered showers
developing as weak upper level shortwaves move through.

More active weather is on the way by Saturday, as a robust Bering
Sea low pushes its front into Southwest Alaska. While it's still a
little too early to hone in on wind speeds and rain amounts,
expect a return of strong, gusty winds and periods of moderate to
heavy rain as this fall storm moves in.

-KC

&&

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

Southerly flow with scattered showers will continue across
Southwest Alaska. Otherwise, focus turns to the next system
entering the Bering Sea Thursday and tracks to the Alaskan west
coast for this weekend. Recent model consensus is converging into
agreement for a slightly more southerly track across the Bering
Sea.

The low is tracking toward the Pribilofs and into the vicinity of
the Kuskokwim Delta. Gale force winds appear likely for the
southern and eastern Bering Seas, including Bristol and Kuskokwim
Bays. Stronger gusts are expected along the Alaska Peninsula, the
western capes, and perhaps even through Etolin Strait. Cold Bay
and Nelson Lagoon gaps could have enhanced gusts from around
midnight Friday overnight through Saturday morning.

Plenty of moisture will be associated with this system with many
areas having one to two inches of rain expected near the Southwest
coast over through Saturday. Upslope flow enhancement along the
Kuskokwim and Kilbuck mountains will lead to the higher range of
precipitation amounts around Cape Newenham to Togiak to
Dillingham. With a more southerly track, consequentially, there is
lower confidence with the forecast QPF and peak winds from
Kuskokwim Bay north. QPF outcome near Bethel could vary as well
and it will depend on whether the winds will be from a southerly
to southwesterly direction. Overall, a wet and active weather
pattern looks to continue for the foreseeable future.

rux

&&

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

The closed upper level low over Norton Sound weakens and
dissipates as the longwave trough pushes across Alaska into
Western Canada by the end of the forecast period. A second upper
level low in the Russian Arctic extends another trough through the
West and Central Bering by midweek. A number of shortwaves
transit the flow, supporting surface features through Wednesday.
The ensemble means has a good handle on the expected changes
across the region. The most significant is a well developed front
moving into Western Alaska Sunday. Locally heavy rains spread
inland from the coast through the Yukon and Kuskokwim Valleys and
Bristol Bay into the Interior, diminishing by midweek. However,
the more concerted heavy rainfall is expected through Cook Inlet
to the Alaska Range, then across the Southcentral coasts by
Wednesday. Heaviest rainfall is expected along the Eastern Kenai
Peninsula into Western Prince William Sound for Sunday and Monday,
and dissipates by Wednesday across the Copper River Basin. In the
far West, another well developed frontal system moves over the
Western Aleutians with locally heavy rains late Sunday, and the
Central Aleutians for Monday. This system diminishes as it moves
East into Southwest Alaska for Wednesday.

- Kutz

&&

.AVIATION...

PANC...
The biggest weather challenge today through early Thursday
evening will once again be winds. The Turnagain Arm winds are
still around, but are mixing both horizontally and vertically
around western Anchorage. This will continue to produce Low Level
Wind Shear (LLWS) at varying levels and directions around the
terminal. If the surface winds do go gusty southeast late this
evening, it will mitigate the wind shear as wind at all low
levels should be from basically a southeast direction. The
Turnagain Arm winds should diminish overnight so even if the
southeast surface winds do not develop and the LLWS persists
longer into the evening, it should end around midnight. These
southeast winds will also help keep ceilings higher at VFR levels
through the evening. Otherwise ceilings should drop to MVFR levels
in the rainfall, which will persist through the morning and then
taper off thursday afternoon.

&&

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
918 PM AKDT Wed Aug 7 2024

AKZ102-082000-
Anchorage-
Including the cities of Anchorage, Eagle River, Indian,
and Eklutna
918 PM AKDT Wed Aug 7 2024

...Ponding of water on roadways and in low lying areas...

Periods of moderate rain will continue over the Anchorage area
tonight and into Thursday afternoon. The heaviest rain is expected
to fall tonight and into Thursday morning. Expect ponding of
water on roadways and minor flooding in low lying and poor
drainage areas. Be aware of your surroundings and do not drive on
flooded roads or ride through flooded trails/paths.