Thunderstorms formed along the fringes of an area of upper-level low pressure drifting across southern Nebraska during the afternoon. Nearly saturated lapse rates through a deep layer promoted heavy rainfall from storms, which drifted northwest across the Sioux Falls metro area late in the afternoon.
Every event with a place to put it. 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.
Thunderstorms formed along the fringes of an area of upper-level low pressure drifting across southern Nebraska during the afternoon. Nearly saturated lapse rates through a deep layer promoted heavy rainfall from storms, which drifted northwest across the Sioux Falls metro area late in the afternoon. Two cells merged across southwest Sioux Falls and produced excessive rainfall along with widespread flash flooding.
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 19, 1:17 PM CST, 2 hours 9 minutes earlier.
Area Forecast Discussion National Weather Service Sioux Falls SD 217 PM CDT Sun Aug 19 2018 .SHORT TERM...(This evening through Monday) Issued at 216 PM CDT Sun Aug 19 2018 Upper level low pressure was deepening over the Western High Plains early this afternoon. This was spreading deeper moisture northward into the area. A more widespread rainfall will struggle a bit to move northeast into drier air but most locations should see some rainfall. Some of the heavier rainfall will be near Interstate 29 this afternoon. As low pressure deepens over northwest MO and southwest IA tonight the more organized area of rain and thunderstorms should develop across northwest IA. Right now not expecting any flash flooding issues as the model soundings hinting that as the low pressure deepens to the south a stronger northeast flow in the low levels could advect some of that drier air back into the region and and keep rainfall rates at a moderate to lower end heavy rate. Will still need to watch out in these areas though as the environment does support heavier rainfall and if the drier air is not as deep then heavier rates will be possible. During the afternoon a few funnel clouds will be possible with surface to 3 km CAPE values around 175 J/kg and fairly low LFC heights. With very weak wind shear any funnels that could touch down would be very brief and difficult if not impossible to detect on radar. The effects of the low pressure will be slow to shift east on Monday and areas east of Interstate 29 may be a bit wet for the morning. Clouds will also be a bit slower to exit and will limit afternoon temperatures. Will have the warmest readings in central SD, the mid 70s, while parts of northwest IA and southwest MN may only reach the upper 60s. .LONG TERM...(Monday night through Sunday) Issued at 216 PM CDT Sun Aug 19 2018 With the exception of Thursday night, Monday night through next weekend looks to be mostly dry. A fast moving system will swing through on Thursday and could linger into Friday. It's a bit far out to be too concerned but a few severe storms will be possible so will be a time frame to watch out for. Otherwise looks like a warming trend through the period with temperatures at or slightly above normal. && .AVIATION...(For the 18Z TAFS through 18Z Monday afternoon) Issued at 1230 PM CDT Sun Aug 19 2018 Showers and isolated thunderstorms will continue to spread northward into the area this afternoon, becoming widespread into the evening hours. Low-end VFR to MVFR conditions are expected for most of the period. Behind the frontal boundary, MVFR ceilings are expected to prevail for the remainder of the TAF period, along with gusty north/northeast winds. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && SHORT TERM...08 LONG TERM...08 AVIATION...05
Hazardous Weather Outlook National Weather Service Sioux Falls SD 443 AM CDT Sun Aug 19 2018 IAZ001>003-012>014-020>022-031-032-MNZ071-072-080-081-089-090-097- 098-NEZ013-014-SDZ038>040-050-052>071-200945- Lyon IA-Osceola-Dickinson-Sioux-O'Brien-Clay IA-Plymouth-Cherokee- Buena Vista-Woodbury-Ida-Lincoln MN-Lyon MN-Murray-Cottonwood- Nobles-Jackson-Pipestone-Rock-Dixon-Dakota-Beadle-Kingsbury- Brookings-Gregory-Jerauld-Sanborn-Miner-Lake-Moody-Brule-Aurora- Davison-Hanson-McCook-Minnehaha-Charles Mix-Douglas-Hutchinson- Turner-Lincoln SD-Bon Homme-Yankton-Clay SD-Union- 443 AM CDT Sun Aug 19 2018 This Hazardous Weather Outlook is for portions of northwest Iowa, west central Iowa, southwest Minnesota, northeast Nebraska, central South Dakota, east central South Dakota, south central South Dakota, and southeast South Dakota. .DAY ONE...Today and Tonight Showers and thunderstorms will gradually expand in coverage today, becoming more numerous from west to east late today and tonight. Severe weather is not expected, but pockets of heavy rainfall could dot the area under slow moving or training showers. .DAYS TWO THROUGH SEVEN...Monday through Saturday Showers and a few thunderstorms will gradually subside on Monday from west to east. Severe weather is not expected. Overall, the low pressure system causing the rainfall will likely produce a widespread average of three quarters, to inch and a half of rainfall over the area through Monday. However locally heavier amounts of 2 to 4 inches could certainly occur where showers would happen to redevelop over the same locations. Therefore stay alert for possible future statements or warnings once these areas are refined. .SPOTTER INFORMATION STATEMENT... Spotter activation will likely not be needed but rainfall amounts are welcome.
Special Weather Statement National Weather Service Sioux Falls SD 328 PM CDT Sun Aug 19 2018 IAZ001>003-012>014-020>022-031-032-MNZ071-072-080-081-089-090-097- 098-SDZ040-055-056-061-062-066-067-071-192230- Lyon IA-Osceola-Dickinson-Sioux-O'Brien-Clay IA-Plymouth-Cherokee- Buena Vista-Woodbury-Ida-Lincoln MN-Lyon MN-Murray-Cottonwood- Nobles-Jackson-Pipestone-Rock-Brookings-Lake-Moody-McCook- Minnehaha-Turner-Lincoln SD-Union- 328 PM CDT Sun Aug 19 2018 Scattered thunderstorms forming near the I-29 corridor may produce brief funnel clouds through sunset. Any funnel clouds that develop are expected to be weak and are unlikely to touch the ground. However if you feel your safety is threatened please seek shelter.
The Sioux Falls radar (KFSD), 10 km away, was scanning. The volume nearest the first event began at 21:26 UTC.
6 flash flood. Local standard time, as filed.
Water reported over curb height, with up to a foot of water over the road.
Water flowing quickly down roads and over curbs.
Reports and pictures in social media of cars stalled with water partially covering headlights.
Water over the curb at the intersection of 45th St. and Marion Road.
A water rescue was performed on three children who fell out of their kayaks while trying to operate in a flooded drainage channel. No injuries were reported.
Three cars stalled in water up to headlight depth near 49th Street and Racket Drive.
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: 780589, 780590, 780593, 780594, 780610, 780596.