Scattered thunderstorms developed late in the day north of a warm frontal boundary across far northern Nebraska. With elevated instability around 2000 J/kg and deep layer effective shear of 40 knots, storms took on a brief supercell structure and favored large hail.
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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.
Scattered thunderstorms developed late in the day north of a warm frontal boundary across far northern Nebraska. With elevated instability around 2000 J/kg and deep layer effective shear of 40 knots, storms took on a brief supercell structure and favored large hail.
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 30, 5:40 PM CST, 26 minutes earlier.
AREA FORECAST DISCUSSION National Weather Service Sioux Falls SD 640 PM CDT Mon Aug 30 2021 .SHORT TERM...(This Evening through Tuesday) Issued at 332 PM CDT Mon Aug 30 2021 Severe weather overnight is the primary focus through Tuesday. 2030 UTC visible satellite picture shows a large field of mid level clouds across southeastern South Dakota into portions of northwestern Iowa. This denotes the northern edge of the elevated mixed layer. The 18Z LBF and UNR soundings both shows lapse rates of 8.5-9 C/km between 700 and 500 mb and models show lapse rates up to 8 C/km reaching south central South Dakota by this evening. The surface warm front appears to be location south of Winner SD toward ONeill NE with the 850 mb likely already into south central SD. At the same time, WV imagery shows a jet streak moving into the Nebraska panhandle. While a few high based showers or storms will be possible within the mid-level cloud field through this evening, the focus for severe convection will be south of this area. Forcing in the left exit of this jet streak is expected to erode the cap in place near the warm front toward sunset. Storms should start out discrete due to the cap in place. With MUCAPE over 2000 J/kg and effective shear around 40 kts, elevated supercells are possible with the initial convection and these storms would move southeast into Nebraska. Some upscale growth is expected overnight with storms spreading ESE into the Missouri Valley toward KSUX. The uncertainty with this forecast is the location of convective initiation and how fast storms grow upscale. The most likely area based upon estimates of the location of the 850 mb front from observations would be near or south of 9V9. Storms in south central South Dakota are likely to remain discrete for an hour or two and take on supercell characteristics which would favor very large hail up to 2" in diameter. There is also a damaging wind risk although the stable layer after sunset deepens to 2 km so expect any wind threat to be isolated. As the night progresses storms will become more numerous from Yankton to Sioux City. However, the storm interaction should decrease the severe hail threat with 1-1.25 inch hail possible and the potential for isolated wind gusts to 60 mph. While rainfall rates could reach 2"/hr the veering low level jet should keep storms progressive. As the result, rainfall amounts around an inch will be possible near the Missouri River with isolated amounts approaching 2 inches. Storms will exit northwestern Iowa on Tuesday morning. Skies will clear during the morning and into the afternoon. With clouds for at least much of the morning in northwestern Iowa, highs will be only in the mid 70s. More sun to the north and west will allow temperatures to into the 80s. .LONG TERM...(Tuesday Night through Monday) Issued at 332 PM CDT Mon Aug 30 2021 A strong ridge will build over the area Tuesday night and Wednesday as a stronger trough moves into the northwestern US. Strong southerly flow will develop between high pressure in the Great Lakes and low pressure in the lee of the Rockers. This will bring more moisture northward. This will result in warmer lows on Tuesday night in the upper 50s near Hwy 71 to the mid 60s in south central SD. It will be more humid on Wednesday with highs from the upper 70s in southwest Minnesota to the mid 80s along and west of the James River. The next chance for rain will come on Wednesday night as a weak wave move northeastward ahead of the strong trough. Convection that is likely to develop over western SD and Nebraska along a cold front will move northeastward with this wave. The best chance for rain will be west of the James River and along Highway 14 - closer to the front. The chance for rain will slowly spread eastward overnight as the front moves into central South Dakota. The front will slowly move east on Thursday and Thursday night. Both the GEFS and ECMWF show abnormally high moisture content by Thursday evening. The ensemble mean PWs are expected to be between 1.5 and 2 inches which is above the 95th percentile and near max value over the past 30 years. With a slow moving boundary and a strong front moving through, thunderstorms are likely with the potential for heavy rainfall with these storms. The location of the heaviest rainfall as well as amounts are still too uncertain to speculate at this time. There may also be a severe weather risk as 0-6 km shear will be over 40 kts once again. However, instability may be limited as continuous convection beginning on Wednesday night may limit instability across the area. This may also produce sufficient cloud cover to limit surface warming. Rain may linger into Friday but that is dependent on how fast the trough and surface boundary move eastward. Once this boundary goes through cooler and less humid weather is expected for the holiday weekend with no significant chances for rain seen at this time. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 634 PM CDT Mon Aug 30 2021 Thunderstorms may continue to plague the area through the first half of the TAT period. In the near term, scattered convection centered over KFSD will remain possible for the couple hours before additional thunderstorm chances develop later this evening into the overnight. These would focus closer to the MO River including at KSUX. Have tried to time our TS chances the best possible but currently in an atmosphere where can't rule out something for roughly the next 12 hours. Any thunderstorm activity would stand the risk of sub-VFR ceilings and vsby along with erratic and gusty winds. Otherwise southeast winds between 10 to 20 kts and clearing skies are expected for the daytime hours Tuesday. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...NONE. MN...NONE. IA...NONE. NE...NONE. && SHORT TERM...Schumacher LONG TERM...Schumacher AVIATION...Kalin
Hazardous Weather Outlook National Weather Service Sioux Falls SD 437 PM CDT Mon Aug 30 2021 IAZ020-031-NEZ013-014-SDZ050-057-058-063>065-068>071-312145- Plymouth-Woodbury-Dixon-Dakota-Gregory-Brule-Aurora-Charles Mix- Douglas-Hutchinson-Bon Homme-Yankton-Clay-Union- 437 PM CDT Mon Aug 30 2021 This Hazardous Weather Outlook is for northwest Iowa, west central Iowa, northeast Nebraska, south central South Dakota and southeast South Dakota. .DAY ONE...Tonight. Strong to severe thunderstorms will be possible this evening into the overnight hours. Activity could develop in south central South Dakota around sunset or shortly after, and will then spread down the Missouri River Valley to around Sioux City by after midnight. Large hail up to 2 inch diameter will be the primary threat, with isolated wind gusts as high as 70 mph also possible. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday. No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed. IAZ002-003-MNZ071-072-080-081-089-090-097-SDZ040-312145- Osceola-Dickinson-Lincoln-Lyon-Murray-Cottonwood-Nobles-Jackson- Pipestone-Brookings- 437 PM CDT Mon Aug 30 2021 This Hazardous Weather Outlook is for northwest Iowa, southwest Minnesota and east central South Dakota. .DAY ONE...Tonight. No hazardous weather is expected at this time. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday. No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. IAZ001-012>014-021-022-032-MNZ098-SDZ038-039-052>056-059>062-066-067- 312145- Lyon-Sioux-O'Brien-Clay-Cherokee-Buena Vista-Ida-Rock-Beadle- Kingsbury-Jerauld-Sanborn-Miner-Lake-Moody-Davison-Hanson-McCook- Minnehaha-Turner-Lincoln- 437 PM CDT Mon Aug 30 2021 This Hazardous Weather Outlook is for northwest Iowa, west central Iowa, southwest Minnesota, central South Dakota, east central South Dakota and southeast South Dakota. .DAY ONE...Tonight. Scattered thunderstorms are possible from late this afternoon into the overnight hours. While the overall risk of severe weather is relatively low, an isolated strong to severe storm may be capable of half dollar size hail and winds to 60 mph. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday. No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time.
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
444 PM CDT MON AUG 30 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0441 PM HAIL 8 NW ETHAN 43.62N 98.11W
08/30/2021 E1.00 INCH DAVISON SD TRAINED SPOTTER
QUARTER SIZED HAIL AND HEAVY RAIN.
&&
TRMPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
507 PM CDT MON AUG 30 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0503 PM HAIL 3 NNW ETHAN 43.58N 98.01W
08/30/2021 E1.00 INCH DAVISON SD TRAINED SPOTTER
LOTS OF VARIABLE SIZED HAIL AND HEAVY RAIN,
WITH BIGGEST STONES AS BIG AS QUARTERS.
&&
TRMPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
520 PM CDT MON AUG 30 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0513 PM HAIL 1 NE ETHAN 43.55N 97.97W
08/30/2021 E0.88 INCH DAVISON SD TRAINED SPOTTER
HEAVY RAIN AND HAIL UP TO THE SIZE OF
NICKELS.
&&
TRMPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
547 PM CDT MON AUG 30 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0538 PM HAIL 2 W CLAYTON 43.44N 97.69W
08/30/2021 E1.25 INCH HUTCHINSON SD TRAINED SPOTTER
HAIL UP TO THE SIZE OF HALF DOLLARS, AND
VERY LITTLE RAINFALL.
&&
TRMPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
559 PM CDT MON AUG 30 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0548 PM HAIL 1 S CLAYTON 43.44N 97.66W
08/30/2021 M1.00 INCH HUTCHINSON SD PUBLIC
&&
IRGPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
624 PM CDT MON AUG 30 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0529 PM HAIL 6 S ALEXANDRIA 43.57N 97.79W
08/30/2021 E0.88 INCH HANSON SD PUBLIC
REPORT FROM SOCIAL MEDIA.
&&
IRGThe Sioux Falls radar (KFSD), 68 km away, was scanning. The volume nearest the first event began at 00:08 UTC.
4 hail. Local standard time, as filed.
Crop damage is an estimate from insured losses. Information provided by the United States Department of Agriculture.
Fields were shredded by large hail.
Crops were badly damaged by large hail. Crop damage is an estimate from insured losses. Information provided by the United States Department of Agriculture.
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: 983408, 983409, 983410, 983411.