Flash Flood Warning 4, NWS Sioux Falls, SD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1238 PM CDT Sun May 31 2026

.KEY MESSAGES...

- Isolated to scattered thunderstorms should develop late this
  afternoon into early evening. Large hail up to half dollarand
  damaging winds to 60 mph would be the main hazards. A Level 1
  of 5 risk for severe storms covers most of the area for this
  threat.

- Similar to today, a conditional Level 1 of 5 risk for severe
  storms covers the forecast area Monday afternoon. The chance
  of development looks lower than today, but if a storm can
  form, large hail and isolated damaging winds could occur.

- High chances (50-80%) for rain will persist through the bulk
  of next week. However, severe storm chances continue to look
  low (near 5% or less) through next week. The better chances
  for rainfall appear to be Wednesday in central SD and
  Wednesday night into Thursday area wide.

&&

.DISCUSSION...
Issued at 1235 PM CDT Sun May 31 2026

An active pattern is expected over the next several days, although
severe weather appears to remain a minor threat. Patchy heavy rain
may play the bigger role with each event.

For this afternoon and tonight, a small corridor of low level
convergence and lift will focus near and just east of the James
Valley. Clouds have cleared through early afternoon and temperatures
have risen a touch. Along with this temperature rise is a turn in
the surface winds to a more south to southwest direction vs.
southeast. This is what is aiding in this low level convergence. The
latest model soundings indicate something around 1500-2000 J/kg CAPE
but weak, disorganized shear. This suggests severe weather should
remain limited, but maybe a cell merger or two could produce a
couple of updrafts strong enough to support hail to half dollar
and wind gusts to 60 mph. Stronger storms will likely drift
east or northeast at about 15 mph, so fairly slow moving. With
this slower storm motion in mind, will need to keep an eye on
the locally heavy rain potential. A handful of the latest hi-res
models are showing small areas of 1-3" of rain with this
development. One area to keep a closer eye on will be parts of
Western Lake county, Northeast McCook and western Minnehaha
where 1-3" of rain fell late last night.

The question becomes what will drive development; will it be diurnal
heating, which would allow updrafts to start developing around 19-
21z, or will it be the weak wave which moves into the area closer to
0-3z this evening. The latest HRRR and Nam output agree with the
later start times, with the Nam indicating a stronger cap and less
development, while the RRFS and RAP kick off development a little
sooner with weaker capping. With the clearing that we are seeing in
central SD towards the James Valley we may see some development by
mid to late afternoon as destabilization is more likely. Suspect
some development between about 5-6pm.

One last thing to watch out for, if we can get mid to late afternoon
development, the LFC are marginally low and a weak convergent
boundary should be in parts of south central and southeast SD, so an
isolated funnel or two will be possible.

While a marginal risk for severe weather is in place for Monday,
confidence in the chances of development are very low. A capping
inversion may win out and for now CAPE values only running around
1000 J/kg with continued weak shear, albeit a little bit better than
today.

Another wave moves through Tuesday but weak shear and weak
instability suggest if anything can develop severe weather is very
unlikely.

Wednesday into Thursday looks like the better chance for more clouds
and better rainfall chances. Broad southerly warm advection looks to
bring in some weak elevated instability as low pressure tracks east
through ND. For now not anticipating all day rainfall but should see
off and on chances Wednesday and Thursday as this low tracks by to
the north.

Friday into Sunday will see periodic weaker waves move through the
area with a continuation of relatively weak flow aloft. This
continued weaker shear environment should keep severe weather
threats very limited.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1214 PM CDT Sun May 31 2026

Clouds continue to clear from southwest to northeast. An area of
stratiform rainfall will drift northeast through southwest MN
and northwest IA through mid afternoon. Patchy MVFR conditions
will be possible. Otherwise scattered thunderstorms will become
possible from about the James River to I-29 late afternoon
through early evening, then drift into parts of southwest MN and
northwest IA late evening and early overnight. A few of these
storms could be strong to very locally severe with locally heavy
rain likely with the stronger storms. IFR stratus and possibly
fog will fill back in late tonight into Monday morning. No
mention of fog for now as the stratus development will likely
offset this development. Regardless of fog or stratus, an
increased threat for IFR conditions.

&&

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

&&

DISCUSSION...08
AVIATION...08

Hazardous Weather Outlook
National Weather Service Sioux Falls SD
133 PM CDT Sun May 31 2026

IAZ001>003-012>014-020>022-031-032-MNZ071-072-080-081-089-090-097-
098-NEZ013-014-SDZ038>040-050-052>071-011845-
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-
133 PM CDT Sun May 31 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...This afternoon and tonight.

A Level 1 of 5 risk for severe storms is in place for late this
afternoon and evening. Isolated to scattered thunderstorms should
develop late this afternoon between the James River and I-29, then
progress eastward through the evening. A very isolated stronger
storm could produce hail to half dollar and wind gusts to 60 mph.
Locally heavier rain will also be possible with small swaths of one
to three inches of rainfall.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

There is a low chance for storms again Monday afternoon. Similar to
today, confidence in storm development is low. However, if storms
can develop, isolated damaging winds and large hail would be the
main threats.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

Preliminary Local Storm Report
National Weather Service Sioux Falls SD
457 PM CDT Sun May 31 2026

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

0435 PM     Hail             2 NNW Emery             43.63N 97.64W
05/31/2026  E0.88 Inch       Hanson             SD   Trained Spotter

&&

TRM

Preliminary Local Storm Report
National Weather Service Sioux Falls SD
515 PM CDT Sun May 31 2026

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

0507 PM     Hail             2 W Vilas               44.01N 97.63W
05/31/2026  M1.25 Inch       Miner              SD   Trained Spotter

&&

TRM

Preliminary Local Storm Report
National Weather Service Sioux Falls SD
545 PM CDT Sun May 31 2026

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

0530 PM     Hail             1 WSW Emery             43.60N 97.63W
05/31/2026  E1.00 Inch       Hanson             SD   Trained Spotter

            Very heavy rain along with penny to quarter
            sized hail. Rainfall is already over 3
            inches.

&&

TRM