A weak disturbance moving northeast from Nebraska along with a weak surface trough ignited convection during the evening hours. As a weakening area of showers and storms moved into the Sioux Falls area, an isolated thunderstorm intensified and produced a small-scale burst of damaging winds.
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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.
A weak disturbance moving northeast from Nebraska along with a weak surface trough ignited convection during the evening hours. As a weakening area of showers and storms moved into the Sioux Falls area, an isolated thunderstorm intensified and produced a small-scale burst of damaging winds.
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 3, 5:30 PM CST, 4 hours 18 minutes earlier.
Area Forecast Discussion National Weather Service Sioux Falls SD 630 PM CDT Fri Aug 3 2018 .SHORT TERM...(This evening through Saturday) Issued at 250 PM CDT Fri Aug 3 2018 A very warm and relatively quiet day has prevailed today as the ridge aloft continues to move eastward and southerly warm and humid air filters in. Strong low-level heating and abundant moisture with dewpoints in the upper 60s and low 70s have dominated the area ahead of a surface trough. Shear is meager (20-25 knots) but very steep mid-layer lapse rates combined with abundant moisture will continue to bring the potential for strong to severe storms. This activity is more likely during the evening hours, which is when the mid-level capping weakens and the mid-upper level shortwave over north central NE/ southcentral SD finally makes its way into the CWA. Upper level pattern is becoming quasi-zonal; therefore developing several mid to upper level perturbations/disturbances that will keep a very unstable airmass over the region. Ahead of the first shortwave, isolated storms will continue to develop this afternoon along the Missouri River area/ west of the James. However convection looks more reasonable after 23Z Friday along and east of the James River, then spreading east-northeast into the overnight hours as the second disturbance moves over the CWA. Scattered strong to severe storms will be possible along and west of a line from Yankton-Sioux Falls- Windom. With large MUCAPE values in the hail growth zone and DCAPE over 1000-1250 J/kg, hail up to golf ball size and damaging winds to 70 mph are the main threats. Severe weather threat will diminish towards the nighttime hours. As we head into the overnight hours through early Saturday morning, showers and thunderstorm coverage increases with the support of the strong LLJ. The main concern during this time frame is the potential for moderate to heavy rainfall, which is supported by PWAT values of 1.4 - 1.7 inches. Additional thunderstorms could spark Saturday afternoon and evening, though confidence remain low as it is conditional to destabilization and cloud debris. .LONG TERM...(Saturday night through Friday) Issued at 250 PM CDT Fri Aug 3 2018 For the extended, Sunday through Tuesday, the pattern remains active as several shortwave troughs move along the quasi-zonal flow aloft. As typical with this type of pattern, model solutions differ in timing and strength. At this point, thunderstorms are possible Saturday evening into Sunday with increasing chances by Sunday afternoon into the evening hours as the main upper shortwave trough moves through. Main impacts are expected along and south of I-90 and northwest Iowa. In terms of severe weather potential, both, Saturday evening and Sunday evening have good scenarios for a few strong to severe storms, but again details at this point are not clear. Wednesday and beyond, northwest flow aloft builds in as the upper ridge settles over the Four Corners. This pattern will result in relatively drier conditions for the remainder of the week. Temperatures through the period will be near to slightly above normal. Highs will range in the 80s and low 90s. Lows mainly in the 60s. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 627 PM CDT Fri Aug 3 2018 Typically tricky aviation forecast ahead with summertime showers and storms expected across much of the area through most of the TAF period. Showers and storms should mostly stay to the east of HON and only have a few hours of VCSH there to cover any issues. Have attempted to restrict mention of thunder at FSD and SUX to 4 hour tempo groups where probability is greatest. Still, given the expected scattered nature of showers and storms, any visibility reductions at those terminals should be brief. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && SHORT TERM...05 LONG TERM...05 AVIATION...Ferguson
Hazardous Weather Outlook National Weather Service Sioux Falls SD 321 PM CDT Fri Aug 3 2018 MNZ071-072-097-SDZ038>040-050-052>061-063>065-068-042030- Lincoln MN-Lyon MN-Pipestone-Beadle-Kingsbury-Brookings-Gregory- Jerauld-Sanborn-Miner-Lake-Moody-Brule-Aurora-Davison-Hanson- McCook-Charles Mix-Douglas-Hutchinson-Bon Homme- 321 PM CDT Fri Aug 3 2018 This Hazardous Weather Outlook is for portions of southwest Minnesota, central South Dakota, east central South Dakota, south central South Dakota, and southeast South Dakota. .DAY ONE...This Afternoon and Tonight Scattered storms will continue to develop this evening through the overnight hours. Some of the stronger storms could become severe with large hail up to golf ball size and damaging winds to 70 mph. Locally heavy rain will also be possible. .DAYS TWO THROUGH SEVEN...Saturday through Thursday Periodic thunderstorm chances continue across the area Saturday through Monday. A few strong to severe storms will be possible Saturday evening and Sunday. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed between 6 pm and 12 am tonight. MNZ080-081-089-098-SDZ062-066-067-069-070-042030- Murray-Cottonwood-Nobles-Rock-Minnehaha-Turner-Lincoln SD-Yankton- Clay SD- 321 PM CDT Fri Aug 3 2018 This Hazardous Weather Outlook is for portions of southwest Minnesota and southeast South Dakota. .DAY ONE...This Afternoon and Tonight Scattered storms are expected to continue this evening through the overnight hours. An isolated strong to severe storm will be possible, with damaging winds to 60 mph and hail to half dollar size. Locally heavy rain will also be possible. .DAYS TWO THROUGH SEVEN...Saturday through Thursday Periodic thunderstorm chances continue across the area Saturday through Monday. A few strong to severe storms will be possible Saturday evening and Sunday. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed between 6 pm and 12 am tonight. IAZ001>003-012>014-020>022-031-032-MNZ090-NEZ013-014-SDZ071- 042030- Lyon IA-Osceola-Dickinson-Sioux-O'Brien-Clay IA-Plymouth-Cherokee- Buena Vista-Woodbury-Ida-Jackson-Dixon-Dakota-Union- 321 PM CDT Fri Aug 3 2018 This Hazardous Weather Outlook is for portions of northwest Iowa, west central Iowa, southwest Minnesota, northeast Nebraska, and southeast South Dakota. .DAY ONE...This Afternoon and Tonight Scattered storms will be possible after midnight tonight. The risk of severe weather tonight is low. .DAYS TWO THROUGH SEVEN...Saturday through Thursday Periodic thunderstorm chances continue across the area Saturday through Monday. A few strong to severe storms will be possible Saturday evening and Sunday. .SPOTTER INFORMATION STATEMENT... Spotter activation is not anticipated tonight.
The Sioux Falls radar (KFSD), 3 km away, was scanning. The volume nearest the first event began at 03:46 UTC.
1 thunderstorm wind. Local standard time, as filed.
Several large trees were blown down near the Sioux Empire Fairgrounds with damage to a few midway rides. Additional tree damage was reported near Elmwood Golf Course. The Sioux Empire Fair was closed at 1035 pm prior to approach of the storms.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in South Dakota in 2018Every state in 2018This day in weather historyWarnings in South Dakota, August 2018
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: 779067.