Weakening clusters of evening thunderstorms moved out of South Dakota and Minnesota into northwest Iowa. A few storms produced hail and damaging wind.
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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.
Weakening clusters of evening thunderstorms moved out of South Dakota and Minnesota into northwest Iowa. A few storms produced hail and damaging wind.
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 Aug 5, 9:51 PM CST, 1 hour 31 minutes earlier.
AREA FORECAST DISCUSSION National Weather Service Sioux Falls SD 1051 PM CDT Thu Aug 5 2021 .SHORT TERM...(This Evening through Friday) Issued at 244 PM CDT Thu Aug 5 2021 Attention for the remainder of the daytime hours revolves around any thunderstorm chances and a low chance of strong to severe storms. As of mid afternoon, a weak boundary/convergence zone was located from south central SD into west central MN with a small cluster of weak convection located just ahead of it in Lyon County MN. Radar and satellite intensity trends have been exhibiting a downward trend however. MLCAPE ahead of this cluster is generally on the order of 1000-1500 J/kg with still some weak SBCIN. Effective deep layer shear is unimpressive at less than 25 kts and thus suspect we won't see much organization to any convection through the evening hours. Any severe risk would likely originate from gusty wind potential with DCAPE values up to 1300 J/kg. Not out of the question to get some smaller hail on any initial updrafts but wind gusts to 60 mph appear to be the primary risk (again, if any stronger storms to develop). Overnight, another bout of mid level WAA may drive additional weak showers/storms into the morning hours Friday but not expecting anything approaching severe levels with this activity. Depending on overnight cloud cover, may see some patchy fog with SREF probabilities favoring NW IA. Bulk of the day Friday should remain dry as shortwave ridge axis moves overhead. HRRR smoke model again painting upper level wildfire smoke providing for hazy skies. Afternoon high temperatures likely sneak a couple degrees higher than today's values or mid 80s to mid 90s. .LONG TERM...(Friday Night through Thursday) Issued at 244 PM CDT Thu Aug 5 2021 A lead wave begins to approach Friday night into Saturday and again may bring some scattered showers or weak convection. How long this activity sticks around will have significant impacts on Saturday's temperatures and as a result any afternoon convection chances. For now, will stick close to the NBM which is just above the 50th percentile or 80s to near 90 for highs. By mid to late afternoon Saturday, models have come into better agreement with a surface low positioned just off to our NW with a west to east warm front and north to south cold front emanating from it. Guidance perhaps keying in on a couple of different zones of potential convective initiation. One with the surface trough east of I-29 and the other closer to the surface front and main upper wave across central SD. Better 850:700 mb flow resides across NW IA and points southeast with weak and messy shear profiles northwest of there across the remainder of the forecast area. Dewpoints in the upper 60s to near 70 will help drive moderate MLCAPE but the lack of shear may prevent a more organized severe threat. What may instead occur is any initial development may carry a marginal severe hail risk with one or more cold pool driven multicell clusters presenting a wind risk thereafter. Still a lot of questions to be answered regarding the convective evolution Saturday afternoon and evening but for now SPC has highlighted areas along and east of the James River in a Slight risk with a Marginal risk of excessive rainfall from WPC east of I-29. Sunday and Monday again look to be a period influenced by shortwave ridging and thus mostly dry conditions. Our far east counties may get clipped by lingering precipitation chances Sunday as the upper level wave spins east but ensemble probabilities favor this staying just east. Temperatures again from the mid 80s to mid 90s look common. Next wave running along the International Border swings through Tuesday and Wednesday and will likely carry some precipitation chances with it. Poor model agreement precludes much more specifics than that however. Temperatures a few degrees either side of normal from the NBM still seem appropriate at this time. && .AVIATION...(For the 06Z TAFS through 06Z Friday night) Issued at 1043 PM CDT Thu Aug 5 2021 Strong thunderstorms will sink south through northwest IA and northeast NE through about 1 am. After this more garden variety isolated showers and thunderstorms will be possible through about sunrise. Most of Friday into Friday evening should be dry with soem chance for showers and thunderstorms returning later Friday night. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...NONE. MN...NONE. IA...NONE. NE...NONE. && SHORT TERM...Kalin LONG TERM...Kalin AVIATION...08
Hazardous Weather Outlook National Weather Service Sioux Falls SD 1159 PM CDT Thu Aug 5 2021 MNZ071-072-SDZ038>040-050-052>061-063>065-068-069-061200- Lincoln-Lyon-Beadle-Kingsbury-Brookings-Gregory-Jerauld-Sanborn- Miner-Lake-Moody-Brule-Aurora-Davison-Hanson-McCook-Charles Mix- Douglas-Hutchinson-Bon Homme-Yankton- 1159 PM CDT Thu Aug 5 2021 This Hazardous Weather Outlook is for southwest Minnesota, central South Dakota, east central South Dakota, south central South Dakota and southeast South Dakota. .DAY ONE...Tonight. No hazardous weather is expected at this time. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. Showers and thunderstorms are possible Friday night and again on Saturday, with the threat for severe weather returning to the area on Saturday. Quarter sized hail and wind gusts up to 60 mph will be possible. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. IAZ001>003-012>014-020>022-031-032-MNZ080-081-089-090-097-098-NEZ013- 014-SDZ062-066-067-070-071-061200- Lyon-Osceola-Dickinson-Sioux-O'Brien-Clay-Plymouth-Cherokee- Buena Vista-Woodbury-Ida-Murray-Cottonwood-Nobles-Jackson-Pipestone- Rock-Dixon-Dakota-Minnehaha-Turner-Lincoln-Union- 1159 PM CDT Thu Aug 5 2021 This Hazardous Weather Outlook is for northwest Iowa, west central Iowa, southwest Minnesota, northeast Nebraska and southeast South Dakota. .DAY ONE...Tonight. Strong to severe storms are possible late tonight. Amongst the stronger storms, large hail up to golf ball size and damaging wind gusts up to 70 mph are possible. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. Showers and thunderstorms are possible Friday night and again on Saturday, with the threat for severe weather returning to the area on Saturday. Quarter sized hail and wind gusts up to 60 mph will be possible. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time.
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
802 PM CDT THU AUG 5 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0800 PM HAIL 2 E WENTWORTH 43.99N 96.93W
08/05/2021 E1.75 INCH LAKE SD PUBLIC
&&
MMPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
851 PM CDT THU AUG 5 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0835 PM HAIL BALTIC 43.76N 96.73W
08/05/2021 E1.00 INCH MINNEHAHA SD PUBLIC
REPORT VIA SOCIAL MEDIA.
&&
MMPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
907 PM CDT THU AUG 5 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0904 PM HAIL 5 ESE CROOKS 43.64N 96.71W
08/05/2021 E2.50 INCH MINNEHAHA SD PUBLIC
REPORT VIA SOCIAL MEDIA.
&&
MMPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
909 PM CDT THU AUG 5 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0908 PM HAIL 4 WNW ROWENA 43.54N 96.62W
08/05/2021 E1.00 INCH MINNEHAHA SD NWS EMPLOYEE
&&
MMPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
921 PM CDT THU AUG 5 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0910 PM HAIL 4 WNW ROWENA 43.54N 96.62W
08/05/2021 E2.00 INCH MINNEHAHA SD NWS EMPLOYEE
&&
MMPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1135 PM CDT THU AUG 5 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1045 PM TSTM WND GST 5 NW BERESFORD 43.13N 96.84W
08/05/2021 E70 MPH LINCOLN SD TRAINED SPOTTER
TREE REPORTED KNOCKED DOWN.
&&
MMThe Omaha radar (KOAX), 128 km away, was scanning. The volume nearest the first event began at 05:23 UTC.
1 thunderstorm wind. Local standard time, as filed.
Thunderstorm winds brought down a few 4 to 6 inch diameter tree limbs in the Morningside neighborhood of Sioux City. Property damage costs are a rough estimate.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2021Every state in 2021This day in weather historyWarnings in Iowa, August 2021
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: 982022.