Flood in Alaska, September 21 to 22, 2023

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
126 PM AKDT Thu Sep 21 2023

.SHORT TERM.../Through Friday night/ An atmospheric river aimed
squarely at the central and northern panhandle is bringing some
heavy to moderate rains at times (all of it east of Cape
Fairweather). Rain amounts since Wednesday evening have ranged as
high as 3 to 5.5 inches with the highest amounts around Sitka and
Juneau. The heavier rainfall is just starting to make its way
into the southern half of the panhandle. Winds have been an issue
as well mainly for the southern panhandle. Winds up to 25 to 30 kt
have been blowing in Stephens Passage, Southern Chatham,
Frederick Sound, Sumner Strait, and Clarence all day.

The atmospheric river continues to dominate the short range
forecast, but the end is in sight. The northern panhandle and
outer coast including Sitka and Juneau will start to see relief
from the rain this evening. The central and southern panhandle
will have to wait until Friday morning as the front is rather slow
to move out of the area. Additional rainfall of 0.5 to 1.5 inches
for the north and outer coast, and 1 to 3 inches for the central
inner channels is expected through Friday morning.

Of secondary concern is the winds that this front is still
producing. The southern panhandle is still expected to receive the
brunt of the winds, with SE 25 to 30 kt winds for most southern
inner channels. This will not last however as the winds are
expected only through tonight with lighter winds (but still mostly
south) expected Friday and Friday night.

.LONG TERM.../Saturday through Thursday/...The weakening low in
the AK Gulf for the start of the weekend keeps shower activity
over the Panhandle but at much diminished rates. Question for the
mid range is an advancing gale force low from the N Pacific and
its eventual track over the AK Gulf. For Sunday initial wave
pushing up from the south moves first bands of precip in then
pulls west. This is followed by the main gale force low Monday.
For Sunday while fair agreement on continued showers over the
south and eastern coast some indications that this wave will stay
further east before the eventual westward track keeping everyone
under rain showers. For the main system the two solutions are the
low will stay off the Haida Gwaii coast through mid week keeping
some rain over the south and increased winds for the SE Gulf. The
alternate solution is the low tracks northward over the panhandle
while weakening resulting in rain for the entire panhandle again
but a diminished Gulf wind forecast. Ensembles have been depicting
the low eventually moving northward mid week while weakening with
greater spread among operational models. Overall still a typical
fall pattern with mild temps, on and off days of rain, and breezy
winds at times. However no significant rainfall or winds for SE AK
expected through the long range.

&&

.AVIATION...A mixed bag of conditions exist this afternoon as
conditions range from VFR to IFR across the panhandle. Conditions
are expected to continue for the central and southern panhandle
through this evening into tomorrow as the main impacts from this
storm persist. Biggest issues being lowered CIGs and VIS with the
heavier periods of rain. Farther north, calmer weather should
continue through tonight but will have to watch for the potential
development of lower VIS as skies clear and the rain moves out of
the area.

&&

.HYDROLOGY...Area rivers and streams have been showing rises over
the last 12 to 24 hours. Of note is Jordan Creek which as of 1 pm
is just below moderate flood stage and is still rising. Montana
Creek and Auke Lake are showing high flows with both just below
minor flood stage. Falls Creek near Petersburg has also shown a
rather fast rise to near minor flood stage this afternoon. A
Flood warning was issued for the Mendenhall Valley area with
emphasis on Jordan Creek, and a flood advisory has been issued
for Falls Creek. The flood watches remain up through Friday
though the watch for Petersburg, Wrangell, and Kake was extended
into Friday afternoon as the rainfall is expected to linger a bit
longer there.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Watch through Friday morning for AKZ320>325.
     Flood Watch through Friday afternoon for AKZ326-327-329.
MARINE...Small Craft Advisory for PKZ031-033>036-641>643-661>663.

&&

SHORT TERM...EAL
LONG TERM....PRB
AVIATION...SF

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Preliminary Local Storm Report
National Weather Service Juneau AK
633 PM AKDT Thu Sep 21 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0622 PM     Flood            1 SE Mendenhall Valley  58.36N 134.58W
09/21/2023                   Juneau             AK   NWS Employee

            Moderate flooding has been reported around
            Jordan Creek. 1 to 2 homes and several
            businesses in the business complex adjacent
            to the creek appear to be affected. 1 home
            appears to be operating a pump to drain out
            what appears to be a crawlspace. Parking
            areas, yards, a local road, & driveways have
            standing water over them.

&&

JLC