A large high pressure system parked over the Mississippi River Valley, bringing several days of hot, southerly flow across the region. From the afternoon of June 28 to the evening of June 29, the combination of heat and humidity, boosted by recent rain, created dangerous conditions.
Every event with a place to put it; 2 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS FSD wrote it up.
A large high pressure system parked over the Mississippi River Valley, bringing several days of hot, southerly flow across the region. From the afternoon of June 28 to the evening of June 29, the combination of heat and humidity, boosted by recent rain, created dangerous conditions. Some heat index values exceeded 105 to 110 degrees in and near northwest Iowa.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Sioux Falls, SD wrote its last area forecast discussion before the first event at Jun 29, 12:08 PM CST, 52 minutes earlier. Its key messages:
Area Forecast Discussion
National Weather Service Sioux Falls SD
108 PM CDT Mon Jun 29 2026
.KEY MESSAGES...
- Isolated to scattered severe thunderstorms will be possible
very late this afternoon 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.
&&
.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 /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1223 PM CDT Mon Jun 29 2026
The main concerns for this TAF period will be thunderstorms.
Late this afternoon into early evening isolated thunderstorms
will be possible near a surface boundary across parts of east
central SD into southwest MN. Some of these storms could be
strong to severe. Of potentially more concern will be a
secondary cluster of storms in far southeast SD, northeast NE
and northwest IA from roughly 4z through 8z which could
produce large hail and wind gusts to 80 mph. Confidence is low
to moderate on the location and timing, but definitely
something to keep an eye on.
&&
.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.
&&
DISCUSSION...08
AVIATION...08Hazardous Weather Outlook National Weather Service Sioux Falls SD 435 AM 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>071-300945- 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- 435 AM 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...Today and tonight. Heat indices will climb into the triple digits this afternoon to early evening, with readings as high as 105 to 108 degrees from around Sioux City toward Spencer and Storm Lake in northwest Iowa. Take precautions to limit your risk of heat illness if spending time outdoors. Scattered strong to severe thunderstorms may develop evening. If storms are able to develop, the main threats with the strongest storms will be hail up to golf ball size and damaging wind gusts up to 75 mph, but a tornado or two and locally heavy rainfall are also possible. There is an additional low risk for an isolated strong to severe storm late tonight into early Tuesday morning. .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 after 5 pm this afternoon. SDZ038-039-050-052>055-057>061-063>065-068-300945- Beadle-Kingsbury-Gregory-Jerauld-Sanborn-Miner-Lake-Brule-Aurora- Davison-Hanson-McCook-Charles Mix-Douglas-Hutchinson-Bon Homme- 435 AM 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...Today and tonight. Areas of dense fog will reduce visibility to a quarter mile or less early this morning. Conditions are expected to improve after sunrise. There is a low probability that severe storms in central South Dakota could move into areas from Chamberlain to Huron after daybreak. These storms would bring a risk of damaging winds in excess of 70 mph and large hail up to 2 inch diameter if they maintain their current strength. Heat index values will climb into the 90s this afternoon, mainly east of Highway 281. at times Monday afternoon into the evening. Take precautions to limit your risk of heat illness if spending time outdoors. .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 before 9 AM this morning, mainly for areas from around Chamberlain to Huron.
The national radar mosaic for the moment the first event began.
1 heat, 1 excessive heat. Local standard time, as filed.
Dangerous heat index readings reached a brief afternoon peak as high as 106 degrees near Ponca.
Dangerous heat index readings reached afternoon peaks as high as 108 degrees at North Sioux City and Sergeant Bluff.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Nebraska in 2026Every state in 2026This day in weather historyWarnings in Nebraska, June 2026
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 1351740, 1351741.