258
FXUS63 KFSD 071148
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
648 AM CDT Mon Sep 7 2026

.KEY MESSAGES...

- Isolated, non-severe thunderstorms continue across
  northwestern Iowa through daybreak. Severe weather is not
  expected, but locally heavy rain has been occurring and may
  lead to isolated flash flooding.

- Isolated to scattered showers and storms are possible along
  and north of I-90 this morning into early afternoon. Severe
  risk is low.

- Additional scattered and possibly severe storms expected late
  this afternoon across southeastern and south central South
  Dakota, moving east through tonight. Ping pong ball sized
  hail, 60 mph wind gusts, and brief heavy rain are the main
  threats. A tornado or two possible.

- Quiet but continued warm conditions are expected for the rest
  of the work week.

&&

.UPDATE...
Issued at 339 AM CDT Mon Sep 7 2026

An area of showers and storms continues over northwestern IA into
southeastern SD early this morning, tied to a wave and some LL
convergence. Although severe weather is not expected, am concerned
with flash flooding  due to  training storms over northeastern
Woodbury and into northwestern Plymouth county - have seen reports
of over 3 inches since midnight and issued a Flash Flood Warning
through 6 AM for this area. May see further development in this area
into southwestern MN through the morning hours as the 700 mb wave
lifts north.

Further west, watching the activity across western SD/NE which is
tied to the next wave and another segment of the LLJ. This may be
the catalyst for additional showers/storms, mainly north of I-90,
mid-late morning into the early afternoon hours. Severe weather risk
is low with these storms.

Main focus is with the increasing LLJ later this afternoon and
tonight, in tandem with main trough ejection from the Rockies.
Leading wave and LLJ along with a surface boundary and destabilizing
atmosphere should provide the catalyst for showers and storms to
develop. Instability All modes of severe weather are possible from
roughly 5 PM through 1 AM, as initial discrete cells may grow
upscale and move east. Shear at all levels increases through the
evening, and increasing mid level lapse rates will also be
supporting of hail to the size of ping pong balls - possibly larger
if a storm can maintain discrete status for longer. A tornado or two
are possible with surface based storms with curved hodographs and
increasing shear in the lowest levels. 65 mph wind gusts are also
possible. May see some locally heavy rainfall as well, but more
progressive storm motion should help limit widespread concerns.
Localized flash flooding is possible, especially if storms move over
areas which have seen recent heavy rain.

Still questions for Tuesday regarding where the surface boundary
ends up and impacts from overnight/early morning convection. Better
shear looks to be offset from the greatest instability which lies
ahead of the front. Could see a stronger storm or two across
northwestern IA and adjacent areas of central MN/eastern NE/far
southeastern SD in the afternoon and evening.

&&

.DISCUSSION...
Issued at 1246 PM CDT Sun Sep 6 2026

THIS AFTERNOON: Strong convection continues to develop in areas
along but mostly east of I-29 this afternoon.  The area continues to
reside in a moderately unstable environment, but lacks any
meaningful shear and mid-lvl lapse rates.  However, climatologically
significant PWATs are in place, with enough DCAPE to suggest an
increased risk for wet microbursts over the next 1-3 hours in a
narrow corridor from Madison to Sioux Falls, Sioux Center, Cherokee,
Storm Lake, Le Mars, and Sioux City. Rainfall may be the most
impactful hazard this afternoon with 1-2 hr totals of 3-4" already
in portions of southern Minnesota.  Additional convection is likely
to continue to produce 2-4" totals in pockets of NW Iowa, though
cold pool development may help push storms off an area before
extreme values may be produced.  The stronger MCV will also nudge
it`s way northward later this afternoon, and may work to produce
additional northward/northeastward convection with it.

TONIGHT: This shortwave/MCV will drag it`s feet eastward this
evening, with some expected weakening of convection with the lost of
daytime heating and general stabilization of the environment nearby.
However, an increased LLJ may begin to develop after 02Z which
could bring returning elevated showers and isolated
thunderstorms to the CWA late this evening and continuing into
the overnight hours. This activity will likely not be severe,
but any shower could still bring brief heavy rain.

MONDAY-TUESDAY: Elevated shower activity diminishes towards daybreak
as shortwave ridging arrives. An ejecting trough out of the Rockies
will bring additional elevated convection into central and northern
South Dakota into Monday afternoon, perhaps grazing the western CWA.
As the EML gradually erodes into south central SD late in the
afternoon, a few strong to severe storms may develop and track
east southeast into the early overnight hours. As the LLJ
increases after dark, elevated convection may expand in coverage
with continued low- end severe weather risks for Tuesday
morning.

More uncertainty for Tuesday, which is focused moreso on the
location of the surface front and impacts of overnight elevated
convection.  While the primary surface front settles in northwest
Iowa, a secondary stronger dew point gradient arrives later in the
afternoon. Should sufficient clearing develop, then a storm or two
could become stronger by mid-afternoon with activity quickly
tracking southeast by the evening.

EXTENDED: With ongoing convection, no forecast changes made to the
extended as a temporarily reprieve from active weather
develops. Temperatures may still remain near to above normal
for the rest of the work week.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 644 AM CDT Mon Sep 7 2026

Scattered showers and storms continue this morning into early
afternoon, which could lead to MVFR and lower conditions. Additional
scattered storms, some possibly severe with large hail and
damaging wind gusts, develop over south central and into
southeastern SD late this afternoon into this evening, moving
east overnight. Locally heavy rainfall is also possible. Storms
may linger across northwestern IA into the end of the period.

Outside of convection, winds will be southeasterly with gusts 20
to 30 knots.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.

&&

$$

UPDATE...SG
DISCUSSION...Dux
AVIATION...SG