As a cold front trudged southward across the area during the late morning and early afternoon, a few slow-moving thunderstorms developed and became anchored for a brief time across southwestern portions of the Sioux Falls metro area. Rainfall rates in excess of 4 inches per hour occurred, with some significant flash flooding.
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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.
As a cold front trudged southward across the area during the late morning and early afternoon, a few slow-moving thunderstorms developed and became anchored for a brief time across southwestern portions of the Sioux Falls metro area. Rainfall rates in excess of 4 inches per hour occurred, with some significant 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 14, 11:09 AM CST, 1 hour 35 minutes earlier.
Area Forecast Discussion National Weather Service Sioux Falls SD 1209 PM CDT Tue Aug 14 2018 .SHORT TERM...(Today and Tonight) Issued at 311 AM CDT Tue Aug 14 2018 An upper level jet will move across North Dakota into northern Minnesota today which will bring some lift and focus for potential thunderstorm development through the day and evening. This jet streak will help push a cool front at the surface southward which will likely be a focus for afternoon and evening thunderstorm development. Any activity early this morning should be post frontal, elevated activity and should remain north of the area. Low pressure to the south may allow some light showers and isolated thunderstorms into mainly northwest Iowa during the morning and early afternoon hours but coverage should be minimal. One effect that this low pressure may have is spreading clouds north and disrupting day time heating enough to keep afternoon and evening activity more isolated. Will continue with isolated to scattered chances across the area. The main threat with any of these storms will be some dime sized hail and locally heavy rainfall. By late tonight another piece of energy will move in from the west as low pressure to the south moves away from the area. The effects of this wave should be minimal tonight with just some small chances in central SD late. Cooler air will continue to work south and lows will likely be near 60 along highway 14 and in the mid 60s closer to the Missouri River. .LONG TERM...(Wednesday through Monday) Issued at 311 AM CDT Tue Aug 14 2018 This wave will work across the area and could bring some morning showers and isolated thunderstorms near the Missouri River in the morning and could work with day time heating to allow a few afternoon diurnally driven showers and storms to develop. Shear and instability are marginal so the severe threat is minimal. With some capping to be concerned about as well will keep chances mostly in the isolated to scattered range. High temperatures should be near 80. Small chance for showers and thunderstorms will continue into Thursday as cool air remains in place. Severe weather threat again minor. A potentially more organized low pressure will move onto the Plains Sunday into Monday and may bring a more widespread rain and isolated thunderstorm threat. It will be a system to watch. Temperatures on Friday and Saturday should be around normal while Sunday, Monday and Tuesday have a better chance for below normal temperatures. && .AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon) Issued at 1203 PM CDT Tue Aug 14 2018 Front continues to work south through the region, switching winds to a more northerly direction. Along and behind this boundary, scattered showers and thunderstorms will be possible thru the mid evening hours, however with the very hit or miss nature of them, tough to time for any one particular TAF site. VFR conditions will be most common thru the rest of today, however brief heavy rain under any thunderstorm activity could lead to periods of visibility restrictions. By late tonight and early Wednesday morning, some MVFR conditions become possible, mainly south of I-90. Additionally, shower and thunderstorm activity may begin to approach KHON from the west by very late in the period. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && SHORT TERM...08 LONG TERM...08 AVIATION...Kalin
Hazardous Weather Outlook National Weather Service Sioux Falls SD 314 AM CDT Tue Aug 14 2018 IAZ001>003-012>014-020>022-031-032-MNZ071-072-080-081-089-090-097- 098-NEZ013-014-SDZ038>040-050-052>071-150815- 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- 314 AM CDT Tue Aug 14 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 Scattered thunderstorms will be possible across the area this afternoon. A stronger storm could produce hail to the size of dimes. .DAYS TWO THROUGH SEVEN...Wednesday through Monday No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed.
The Sioux Falls radar (KFSD), 9 km away, was scanning. The volume nearest the first event began at 18:41 UTC.
2 flash flood, 1 heavy rain. Local standard time, as filed.
Reports of stalled cars and flash flooding at both the intersection of 41st Street and Marion Road and the intersection of 41st Street and Larch Avenue.
Rainfall of 4.7 inches in less than an hour. Report from social media.
Two apartments extensively damaged by flood waters on lower level.
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: 780567, 780568, 780633.