Flash Flood Warning 10, NWS Sioux Falls, SD

204 
WGUS73 KFSD 210224
FFSFSD

Flash Flood Statement
National Weather Service Sioux Falls SD
924 PM CDT Thu Aug 20 2026

SDC083-125-210415-
/O.CON.KFSD.FF.W.0010.000000T0000Z-260821T0415Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Lincoln SD-Turner SD-
924 PM CDT Thu Aug 20 2026

...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 1115 PM CDT THIS
EVENING FOR WEST CENTRAL LINCOLN AND NORTHEASTERN TURNER COUNTIES...

At 924 PM CDT, gauge reports indicated thunderstorms producing heavy
rain across the warned area. Between 1 and 3 inches of rain have
fallen. Flooding impacts will continue, but no additional rainfall is
expected. Flash flooding is ongoing or expected to begin shortly.

HAZARD...Flash flooding caused by thunderstorms.

SOURCE...Gauges reported.

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...
  Lennox and Chancellor.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

Be aware of your surroundings and do not drive on flooded roads.

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 4333 9692 4336 9700 4344 9715 4350 9715
      4350 9705 4346 9695 4342 9687 4336 9687
      4332 9688

FLASH FLOOD...GAUGE INDICATED

$$

IG

879 
WGUS73 KFSD 210250
FFSFSD

Flash Flood Statement
National Weather Service Sioux Falls SD
950 PM CDT Thu Aug 20 2026

SDC083-125-210300-
/O.CAN.KFSD.FF.W.0010.000000T0000Z-260821T0415Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Lincoln SD-Turner SD-
950 PM CDT Thu Aug 20 2026

...FLASH FLOOD WARNING IS CANCELLED FOR WEST CENTRAL LINCOLN AND
NORTHEASTERN TURNER COUNTIES...

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

&&

LAT...LON 4333 9692 4336 9700 4344 9715 4350 9715
      4350 9705 4346 9695 4342 9687 4336 9687
      4332 9688

$$

IG

...CORRECTION...
Area Forecast Discussion
National Weather Service Sioux Falls SD
211 PM CDT Thu Aug 20 2026

.KEY MESSAGES...

- Isolated thunderstorms could develop this afternoon and
  evening. IF storms are able to develop, two+ inch hail and
  50-70 mph winds are the main hazards. An isolated tornado is
  also possible.

- Warmer temperatures continue on Friday, with another low
  chance (20-30%) for thunderstorms in the afternoon and
  evening along and south of the Missouri River.

- Slightly cooler weather for the weekend. Saturday should
  remain dry with rain chances (40-70%) returning to portions
  of the area by Sunday morning.

- Additional chances for rain, and potentially thunderstorms (5-
  10%), are possible through the first half of next week.
  Details are uncertain, so continue to check the latest
  forecast for the most up to date information.

&&

.DISCUSSION...
Issued at 210 PM CDT Thu Aug 20 2026

A light shower or two persists across southwest Minnesota this
afternoon. These showers remain ahead of a cold front that is just
pushing into the forecast area. This front will serve as the focal
point for potential severe storm development later this afternoon.
The main shortwave is just north and east of the forecast area.
However, the upper level jet will be nosing its exit region into the
southwestern half of the forecast area. This presents a bit of a
displacement in where the better shear and forcing will lie. Some
capping remains across the area but the weakest amount of capping
looks to be just along the front itself. Think that 1 to 4 storms is
possible this afternoon and evening IF storms are able to develop.
IF storms develop, more than sufficient instability will be in place
with CAPE values up to 2,000 J/kg to 2,500 J/kg as moisture pools
ahead of the front. With part of the upper level jet overhead,
vertical shear will also be sufficient with deep layer shear values
between 40 to 50 knots. DCAPE values will be highest along and just
behind the front with magnitudes up to 1,200 J/kg. Thus, Large hail
to 2+ inches and damaging winds to 50-70 mph will be the main
hazards. A low 2% chance exists for a tornado as the low level jet
begins to strengthen this evening, slightly expanding low level
hodographs and increasing 0-3km storm relative helicity (SRH) values
up to 100+ m2/s2. Any chance for severe storms for be waning through
the evening hours as nocturnal stabilization increases capping. The
previously mentioned cold front will stall out over the forecast
area tonight, leaving muggy conditions in place. With light winds
expected, patchy fog is once again possible.

Highs will remain in the 80s across the area on Friday. The
previously mentioned cold front will push through the forecast area
and end up right along the Missouri River. This could result in a
few storms developing on this boundary before quickly pushing off to
the south and east. However, latest LREF probabilities remain low
(20-30%) for a tenth of an inch of rain or more. The HREF shows
little to no probabilities for any precipitation. This is in line
with the latest hi-res guidance as the bulk of this guidance shows
storms developing south of the surface front in Nebraska. Will keep
an eye on this potential in case storms trend back north, but for
now, it looks most likely that the forecast area will remain dry
tomorrow. Low temperatures will fall to the upper 50s and low 60s
overnight.

Saturday will be a dry day as high pressure passes through the
forecast area. High temperatures will be a little cooler, only
warming to the upper 70s to low to mid 80s. The dry conditions will
be brief as the next round of rain will return on Sunday as another
shortwave trough will push into the Northern Plains. Latest
ensembles show a 40-70% chance for rainfall totals to exceed a tenth
of an inch through the day. Latest machine learning (ML) guidance
keeps the highest chances for severe storms to the west of the
forecast area. This may change over the next few days so will
continue to monitor the potential for severe storms on Sunday.

High temperatures will remain near seasonable in the upper 70s and
80s for the first half of next week. Active zonal to northwest flow
will persist aloft as well, contributing to additional risks for
showers and storms. ML guidance does shows a small increase in
potential severe storm risk, though the probabilities only 5 to 10%.
Something to keep an eye on going forwards as weak shortwaves within
the active flow can deliver additional chances for potential severe
storms.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1226 PM CDT Thu Aug 20 2026

VFR conditions begin the TAF period. A few light showers persist
across parts of southwest Minnesota but are on the move out. A cold
front is just west of the forecast area but will push into the area
through the first half of the afternoon timeframe. Showers and
thunderstorms may develop along the front later this afternoon and
evening. Confidence is high enough to include in KFSD's TAF at this
time but trends in storm development will be monitored. Chances for
storms will end late this evening, leaving light and variable winds
for the overnight hours. Patchy fog is once again on the table
though confidence is too low to include in a TAF at this time. Light
northerly flow will finish out the TAF period.

&&

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

&&

DISCUSSION...Meyers
AVIATION...Meyers

Hazardous Weather Outlook
National Weather Service Sioux Falls SD
344 AM CDT Thu Aug 20 2026

SDZ038-039-050-052>054-057>060-063-064-210845-
Beadle-Kingsbury-Gregory-Jerauld-Sanborn-Miner-Brule-Aurora-Davison-
Hanson-Charles Mix-Douglas-
344 AM CDT Thu Aug 20 2026

This Hazardous Weather Outlook is for central South Dakota, east
central South Dakota, south central South Dakota and southeast
South Dakota.

.DAY ONE...Today and tonight.

Very isolated storms may develop this afternoon and evening. If a
storm develops, severe weather is possible with 2 inch hail and 70
mph wind gusts the main threats.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

A few strong to severe storms are possible Friday afternoon and
evening, south of I-90.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed Thursday afternoon and evening.

IAZ001>003-012>014-020>022-031-032-MNZ071-072-080-081-089-090-097-
098-NEZ013-014-SDZ040-055-056-061-062-065>071-210845-
Lyon-Osceola-Dickinson-Sioux-O'Brien-Clay-Plymouth-Cherokee-
Buena Vista-Woodbury-Ida-Lincoln-Murray-Cottonwood-Nobles-Jackson-
Pipestone-Rock-Dixon-Dakota-Brookings-Lake-Moody-McCook-Minnehaha-
Hutchinson-Turner-Bon Homme-Yankton-Union-
344 AM CDT Thu Aug 20 2026

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

.DAY ONE...Today and tonight.

Patchy fog, including dense fog with visibility below half a mile
continues through 9 AM.

Isolated to widely scattered storms may develop this afternoon and
evening. Storms may quickly become strong to severe, with 2 inch hail
and 75 mph wind gusts the main threats.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

Patchy fog is possible Friday morning.

A few strong to severe storms are possible Friday afternoon and
evening, south of I-90.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed Thursday afternoon and evening.

Preliminary Local Storm Report
National Weather Service Sioux Falls SD
701 PM CDT Thu Aug 20 2026

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

0648 PM     Hail             Humboldt                43.65N 97.07W
08/20/2026  M1.75 Inch       Minnehaha          SD   Public

&&

ER

Preliminary Local Storm Report
National Weather Service Sioux Falls SD
801 PM CDT Thu Aug 20 2026

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

0725 PM     Tstm Wnd Gst     7 WSW Wall Lake         43.49N 97.08W
08/20/2026  M76 MPH          Turner             SD   Mesonet

            Mesonet station PKMS2 Parker 7NNE (SD
            Mesonet).

&&

JH