Flash Flood Warning 11, NWS Sioux Falls, SD

862 
WGUS73 KFSD 051124
FFSFSD

Flash Flood Statement
National Weather Service Sioux Falls SD
624 AM CDT Sat Sep 5 2026

SDC035-061-067-051345-
/O.CON.KFSD.FF.W.0011.000000T0000Z-260905T1345Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Davison SD-Hanson SD-Hutchinson SD-
624 AM CDT Sat Sep 5 2026

...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 845 AM CDT THIS
MORNING FOR SOUTHEASTERN DAVISON, SOUTHWESTERN HANSON AND
NORTHWESTERN HUTCHINSON COUNTIES...

At 624 AM CDT, Doppler radar indicated thunderstorms producing heavy
rain across the warned area. Between 2 and 4 inches of rain have
fallen. The expected rainfall rate is 0.5 to 1 inch in 1 hour.
Additional rainfall amounts of 0.5 to 1.5 inches are possible in the
warned area. Flash flooding is ongoing or expected to begin shortly.

HAZARD...Flash flooding caused by thunderstorms.

SOURCE...Radar indicated.

IMPACT...Flash flooding of small creeks and streams, urban areas,
         highways, streets and underpasses as well as other poor
         drainage and low-lying areas.

Some locations that will experience flash flooding include...
  Ethan, Dimock and Milltown.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Turn around, don't drown when encountering flooded roads. Most flood
deaths occur in vehicles.

Be especially cautious at night when it is harder to recognize the
dangers of flooding.

Please report observed flooding to local emergency services or law
enforcement and request they pass this information to the National
Weather Service when you can do so safely.

&&

LAT...LON 4350 9806 4356 9806 4362 9779 4351 9771
      4345 9771 4337 9782 4343 9806

FLASH FLOOD...RADAR INDICATED
EXPECTED RAINFALL RATE...0.5-1 INCH IN 1 HOUR

$$

SG

569 
WGUS73 KFSD 051301
FFSFSD

Flash Flood Statement
National Weather Service Sioux Falls SD
801 AM CDT Sat Sep 5 2026

SDC035-061-067-051311-
/O.CAN.KFSD.FF.W.0011.000000T0000Z-260905T1345Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Davison SD-Hanson SD-Hutchinson SD-
801 AM CDT Sat Sep 5 2026

...FLASH FLOOD WARNING IS CANCELLED FOR SOUTHEASTERN DAVISON,
SOUTHWESTERN HANSON AND NORTHWESTERN HUTCHINSON COUNTIES...

The heavy rain has ended. Flooding is no longer expected to pose a
threat. Please continue to heed remaining road closures.

&&

LAT...LON 4350 9806 4356 9806 4362 9779 4351 9771
      4345 9771 4337 9782 4343 9806

$$

IG

Area Forecast Discussion
National Weather Service Sioux Falls SD
424 AM CDT Sat Sep 5 2026

.KEY MESSAGES...

- Thunderstorms continue across South Dakota early this morning.
  Severe risk remains low, but stronger storms may produce heavy
  rain, wind gusts to 65 mph, and hail the size of a quarter.
  Storms are expected to weaken as they approach the I-29
  corridor after sunrise.

- Patchy fog is occurring east of I-29. Visibility may briefly
  fall below 2 miles at times.

- Hot and humid conditions persist this weekend with gradual
  improvement into next work week. Afternoon temperatures in the
  90s push heat index values near 100 at times. Outdoor events
  should plan accordingly to the heat risks but know clouds
  could also impact temperatures today and Sunday.

- Occasional thunderstorms are possible again this evening and
  Sunday, though remain highly unpredictable on location. A few
  stronger storms could be possible, the risk of widespread
  severe weather remains low.

- A shifting pattern may bring higher rain chances, slightly
  cooler temperatures, and a severe weather risk Labor Day into
  early next week.

&&

.UPDATE...
Issued at 423 AM CDT Sat Sep 5 2026

With focus on on-going and occasionally severe convection, only
changes to the forecast have been to maintain updates associated
with that. Storms have been slowly moving east across the forecast
area since midnight - so far the best model has been the 05.00z RRFS
with the convective evolution. Still anticipate downward trend in
severe risk through the morning hours as they move into a more
stable/less favorable environment and the influence of the LLJ
subsides. So far, have seen sporadic wind gusts around 60 mph and
very heavy rainfall. Some personal weather stations across Jerauld,
Davison, and into Hutchinson counties have seen over 2.5-3+ inches
of rain since midnight. Continuing to monitor for flash flooding
risk.

Patchy fog has developed east of I-29, with some visibility below 2
miles at times possible through mid morning.

Main concerns today will be the potential impact of clouds and
convective debris on the highs today and additional convective risk
later in the day and tonight with isolated severe storms possible.

&&

.DISCUSSION...
Issued at 122 PM CDT Fri Sep 4 2026

THIS AFTERNOON: It remains hot and very humid across the Tri-State
area, as temperatures have already risen into the upper 80s to low
90s.  The generally weak surface flow has allowed dew points to
remain in the upper 60s to lower 70s, with even mid-70 dew points in
NW Iowa. Heat index values will continue to rise to 95 to 105
degrees and current heat advisory will remain in place.

Through the region a few clusters of elevated showers and
thunderstorms continue. This activity is tied to both weak vorticity
moving through the High Plains, but also west of a slightly richer
850:700 mb theta-e airmass.  Latest guidance continues to suggest
that cluster of activity just west of the CWA will continue to move
north and northeast but could graze Beadle county later this
afternoon. Activity over south central Nebraska is also expected to
slowly crawl eastward, but without a strong theta-e push, may
diminish by time it would reach Sioux City this evening. The
development of any SFC based convection to the west and north seems
limited given the strong EML in the area. If a storm could go, then
large hail could be possible.

TONIGHT:  There seems to be at least modest agreement in guidance
tonight, suggesting continued mid-lvl theta-e advection will place a
corridor of increased moisture west of I-29 and towards the James
River valley after midnight.  Guidance also seems in agreement that
another weak perturbation will leave Colorado and move northeast,
inducing a 40 knot LLJ that will converge near the western half of
the CWA.  Scattered showers and thunderstorm development would be
favorable by 2-3am in this scenario. Environmental soundings
would suggest anywhere from 1500-2000 J/KG MUCAPE lifted off the
700 mb layer, with modest shear AOA 25-30 knots. This would
favor mostly multicells with some potential supercell
characteristic, with brief bouts of quarter to ping pong ball
hail. Feel perhaps the greatest risk given dry subcloud layer
and steep low-lvl lapse rates would be some brief gusty winds.
Storm motion may be very slow with mean winds only around 10
knots, suggesting that with deep warm cloud depths and
increasing PWATs, some localized heavy rain might be an issue.
HREF/REFS 3hr PMM and max guidance indicates pockets of rainfall
of 2-4" could be possible.

SATURDAY:  Lingering morning activity will continue to pose a few
severe risks in the morning if any cold pool could develop. Though
as the LLJ wanes and veers off, the convection risks may drop by
early afternoon.  Lingering cloud debris, if storms develop, will
pose a challenge to the afternoon forecast with some guidance
keeping this festering cloud cover right through the heart of the
CWA.  Currently forecast highs in the 90s are contingent on less
cloud cover by mid-day.  If cloud cover doesn't impact us as much,
then another advisory could be needed south of I-90 as dew points
remain in the 70s.  Subsidence appears to remain in place for most
of Saturday night, though the LLJ may once again spur isolated to
scattered convection by daybreak Sunday. The various mesoscale waves
topping the ridge into Sunday also pose an issue, with one or more
convective clusters moving east and southeast out of North Dakota by
daybreak.

SUNDAY: Uncertainty grows on Sunday with the Tri-State are remaining
under the synoptic ridge.  Convection on the periphery of this ridge
will pose both a risk of dipping into the eastern CWA early Sunday,
but moreso throwing a convective outflow boundary westward. If a
boundary develops, it would certainly pose a risk for redevelopment
later in the day despite a continued EML overhead. There remains far
too much uncertainty in the forecast to be much more specific on
severe weather risks, but those with outdoor plans should continue
to monitor. Again, convection will have some impact on
temperatures, but another day with highs in the upper 80s to
lower 90s will be possible.

MONDAY-TUESDAY: The apex of the mid-lvl ridge slides east of the Tri-
State by Monday as a deep upper trough moves into the Northern.
Rockies. What will this pattern shift signal for us?  Lee-side
troughing will induce stronger return flow into the Plains,
with gusty surface winds by Monday afternoon. An approaching
front late on Monday into Monday night could spur isolated to
scattered thunderstorms over the Dakotas and Nebraska. Should
boundary layer moisture not mix-out too significantly, a severe
weather risk may develop into Tuesday night. Those limitations
to any widespread risks may be the fact the deepest moisture
transport is pushed north of the CWA along with the strongest
forcing, suggesting lift along the boundary may be weaker
further south. Temperatures will remain in the upper 80s, with
the front moving southeast Tuesday. Again, we'll watch the
positioning of this boundary for potential convection Tuesday
afternoon.

WEDNESDAY-THURSDAY: Continued signals for a slight cooldown for the
middle of the week behind the passing front. Stronger CAA may allow
for highs to fall back to the 70s and lower 80s.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1238 AM CDT Sat Sep 5 2026

Light southeast winds will begin to increase ahead of an approaching
wave. Diurnally driven winds continue to increase through
Saturday afternoon. Gusts of 15-22 kts are expected along I-29
and west. Gusts generally less than 15 kts to the east. East of
I-29 where winds are lighter may see some early morning fog
development. This should burn off by mid-morning.

As of TAF issuance a few thunderstorms are ongoing over central
South Dakota, moving northeast. A few storms may become strong to
severe producing heavy downpours, wind gusts to 60 mph, and hail the
size of a half dollar. If a stronger updraft can develop hail to the
size of a ping-pong ball is possible. Ceilings and visibilities
under storms, and in areas of fog, could degrade to MVFR to
IFR. Storms should clear out by Saturday afternoon. VFR
conditions will then prevail for the remaining period.

&&

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

&&

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

Hazardous Weather Outlook
National Weather Service Sioux Falls SD
428 AM CDT Sat Sep 5 2026

IAZ001>003-012>014-020>022-031-032-MNZ071-072-080-081-089-090-097-
098-NEZ013-014-SDZ038>040-050-052>071-060930-
Lyon-Osceola-Dickinson-Sioux-O'Brien-Clay-Plymouth-Cherokee-
Buena Vista-Woodbury-Ida-Lincoln-Murray-Cottonwood-Nobles-Jackson-
Pipestone-Rock-Dixon-Dakota-Beadle-Kingsbury-Brookings-Gregory-
Jerauld-Sanborn-Miner-Lake-Moody-Brule-Aurora-Davison-Hanson-McCook-
Minnehaha-Charles Mix-Douglas-Hutchinson-Turner-Bon Homme-Yankton-
Union-
428 AM CDT Sat Sep 5 2026

This Hazardous Weather Outlook is for northwest Iowa, west central
Iowa, southwest Minnesota, northeast Nebraska, central South
Dakota, east central South Dakota, south central South Dakota and
southeast South Dakota.

.DAY ONE...Today and tonight.

Thunderstorms continue this morning. Some may be strong to severe
producing heavy rain, wind gusts to 65 mph, and hail to the size of
a quarter.

Some patchy fog will reduce visibility through mid morning east of
I-29.

Heat and humidity lead to heat index values around 100 degrees again
this afternoon and evening.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

Hot and humid conditions are expected through the holiday weekend.
Heat Index values will be in the 90s to around 100 during the
afternoon. Please apply heat safety to your outdoor activities.

Periods of isolated to scattered thunderstorms remain possible
through the holiday weekend into the work week. A stronger storm or
two are possible but widespread severe weather is not expected.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed at times into Monday.

Preliminary Local Storm Report
National Weather Service Sioux Falls SD
407 AM CDT Sat Sep 5 2026

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

0309 AM     Tstm Wnd Gst     3 SE Dimock             43.44N 97.95W
09/05/2026  M61 MPH          Hutchinson         SD   Public

            Personal Weather Station.

0317 AM     Tstm Wnd Gst     1 W Dimock              43.48N 98.01W
09/05/2026  M55 MPH          Hutchinson         SD   Public

            Personal Weather Station.

0331 AM     Tstm Wnd Gst     8 ESE Parkston          43.35N 97.83W
09/05/2026  M54 MPH          Hutchinson         SD   Public

            Personal Weather Station.

0341 AM     Tstm Wnd Gst     8 E Dimock              43.49N 97.83W
09/05/2026  M57 MPH          Hutchinson         SD   Public

            Personal Weather Station.

0349 AM     Tstm Wnd Gst     6 SW Clayton            43.37N 97.73W
09/05/2026  M53 MPH          Hutchinson         SD   Public

            Personal Weather Station.

0402 AM     Tstm Wnd Gst     7 W Clayton             43.42N 97.80W
09/05/2026  M56 MPH          Hutchinson         SD   Public

            Personal Weather Station.

0342 AM     Tstm Wnd Gst     3 S Corsica             43.39N 98.41W
09/05/2026  M53 MPH          Douglas            SD   Dept of Highways

&&