Severe Thunderstorm Warning 137, NWS Sioux Falls, SD

Area Forecast Discussion
National Weather Service Sioux Falls SD
712 PM CDT Mon Jun 29 2026

.KEY MESSAGES...

- Isolated to scattered severe thunderstorms have begun this
  evening and will continue into the overnight hours. The more
  concerning threat will possibly come from about 11 pm through
  4 am in and near northwest IA where wind gusts to 80 mph, hail
  to ping pong ball and locally heavy rain will be possible.

- The heat headlines will continue into this evening. After
  today, the heat index for most of the area should remain below
  100 degrees through the week. There may be a few times when
  heat headlines are needed with the better chances in northwest
  IA. Moderate to major heat risks are expected however through
  the week.

- An active pattern this week leads to periodic threats for
  locally heavy rain and scattered severe storms. At this time
  the better chances appear to be Tuesday night and Thursday
  into Thursday night.

&&

.UPDATE...
Issued at 710 PM CDT Mon Jun 29 2026

As of 7:00 pm CDT, storms have begun to fire along a cold front
draped from Niobrara, Nebraska through Sioux Falls into eastern
North Dakota and western Minnesota. Storms are expected to move
northeast with the front through the next few hours, impacting
eastern South Dakota and western Minnesota and Iowa. Storms have the
potential to become severe and produce winds up to 80 mph, hail up
to the size of ping-pong balls, and brief heavy downpours. Though
the risk is low, a tornado or two cannot be ruled out. This first
round of storms looks to move out of the region by around 11 pm.

A second round of storms are expected to form as a weak wave pushes
northeast out of Nebraska after midnight. Threats will be very
similar, very strong damaging wind gusts, large hail, heavy rain,
and possibly a tornado. This second round is expected to have the
largest impacts along and east of a line from Yankton, to Sioux
Falls, to Marshall, Minnesota. This round should be clear of the
area around or shortly after 7 am Tuesday.

&&

.DISCUSSION...
Issued at 108 PM CDT Mon Jun 29 2026

Late this afternoon and Tonight:

An unstable environment will be in place today as a weak front works
into areas between about the James River and I-29 this afternoon.
This may be a focus for isolated thunderstorms as a weak wave begins
to move northeast from Nebraska ahead of the main wave to the west
of the area. CAPE values sitting around 3000 J/kg with the 0-3km and
0-6km shear values sitting about 30-40 knots. The questions for the
late afternoon and early evening activity will be getting enough
convergence to overcome the capping inversion. However, given these
parameters and a quick look at the model soundings showing a decent
amount of dry air below about 600mb, wind and heavy rain will be the
main threats. Wind gusts to 80 mph and locally heavy rain will be
the main threats. Hail to half dollar will be a threat as well.

Current thoughts are that there will likely be two areas of
convection to watch for. The first will be from roughly 6 pm to 9 pm
along the surface front and more driven by day time heating. This
will likely be near I-29 and is a bit lower confidence given a
strong capping inversion and weak low level convergence. The next,
increasingly more likely threat will be tied to a weak wave moving
out of Nebraska and an increasing LLJ. The better chances for this
will be from about 11 pm to 4 am and this is also when the threat
for the highest winds is expected.

Tuesday into Wednesday:

Tuesday should prove to be a fairly nice, albeit very warm, summer
day with lighter winds and dew points back into the 50s and 60s and
highs from the upper 80s to mid 90s. Currently do not anticipate any
heat headlines but parts of northwest Iowa do get close to a 100
heat index so there will be some potential at least.

Model output continues to point to Tuesday night into Wednesday as a
period with a good chance for showers and thunderstorms. A wave will
rotate northeast through Nebraska and bring a strong increase in the
LLJ into southern SD by about 6z and northwest IA and southwest MN
shortly after. Given the shear profile and expected instability
around 2500 J/kg, a few severe storms will be possible. The low
level remain fairly dry so given the amount of instability we may
see some potential for 75 to 80 mph winds as well as pin pong ball
sized hail.

Wednesday afternoon and evening may see some scattered showers and
storms with the better chances in northwest IA as a front lingers
after the likely morning showers and storms. With the threat for
clouds and a post outflow air mass, heat headlines are again not
expected.

Thursday into the weekend:

The next good chance for showers and thunderstorms moves in Thursday
into Thursday night as another well agreed upon wave moves through.
Will likely continue the threat for locally heavy rain and isolated
severe thunderstorms depending upon where any outflow boundaries end
up.

Friday into the weekend continues the trends of near daily waves as
the upper level flow transitions to a bit more westerly direction.
This hints at a chance for showers and storms Friday and Saturday
with a potential break by Sunday into Monday as a weak ridge aloft
builds in. For now this time frame is pretty low confidence given
all of the activity tonight through Thursday night.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 648 PM CDT Mon Jun 29 2026

Showers and thunderstorms have begun to fire in northeast Nebraska
along a cold front draped from there through eastern South Dakota
and North Dakota. These storms are expected to move northeast and
continue to form along the front. KHON does not look to be impacted
but KFSD and KSUX could begin to see storms in the next 2-5 hours.
Risks include damaging wind gusts up to 70 kts, hail up to a half
dollar, and brief heavy downpours. Storms move northeast through the
region, and should be out of the region shortly before sunrise.

VFR conditions are expected to prevail through the period except
under areas experiencing thunderstorms.

Gusty southerly winds will decrease and become light and variable
overnight. After sunrise they will become more westerly but remain
light.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Heat Advisory until 9 PM CDT this evening for SDZ039-040-
     054>056-060>062-065>070.
     Extreme Heat Warning until 9 PM CDT this evening for SDZ071.
MN...Heat Advisory until 9 PM CDT this evening for MNZ071-072-080-
     081-089-090-097-098.
IA...Heat Advisory until 9 PM CDT this evening for IAZ001>003.
     Extreme Heat Warning until 9 PM CDT this evening for
     IAZ012>014-020>022-031-032.
NE...Heat Advisory until 9 PM CDT this evening for NEZ013.
     Extreme Heat Warning until 9 PM CDT this evening for NEZ014.

&&

UPDATE...AJP
DISCUSSION...08
AVIATION...AJP

Hazardous Weather Outlook
National Weather Service Sioux Falls SD
717 PM CDT Mon Jun 29 2026

IAZ001>003-012>014-020>022-031-032-MNZ071-072-080-081-089-090-097-
098-NEZ013-014-SDZ040-056-062-066-067-069>071-010030-
Lyon-Osceola-Dickinson-Sioux-O'Brien-Clay-Plymouth-Cherokee-
Buena Vista-Woodbury-Ida-Lincoln-Murray-Cottonwood-Nobles-Jackson-
Pipestone-Rock-Dixon-Dakota-Brookings-Moody-Minnehaha-Turner-Yankton-
Union-
717 PM CDT Mon Jun 29 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...Tonight.

Strong to severe thunderstorms may develop this evening. The primary
threats with the strongest storms will be hail up to ping-pong ball
size, damaging wind gusts up to 80 mph, and brief heavy downpours.
Though the risk is low, a tornado or two cannot be ruled out. Storms
may continue into the early morning hours of Tuesday.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

Isolated severe storms are possible again Tuesday night, and perhaps
again on Wednesday, but confidence in any details is low at this
time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed.

SDZ038-039-050-052>055-057>061-063>065-068-010030-
Beadle-Kingsbury-Gregory-Jerauld-Sanborn-Miner-Lake-Brule-Aurora-
Davison-Hanson-McCook-Charles Mix-Douglas-Hutchinson-Bon Homme-
717 PM CDT Mon Jun 29 2026

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

.DAY ONE...Tonight.

Hazardous weather is not expected at this time.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

Isolated severe storms are possible again Tuesday night, and perhaps
again on Wednesday, but confidence in any details is low at this
time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.