Winds backing ahead of a strong upper level wave along with approach of a upper level jet streak increased late-day shear and supported development of an initially isolated severe thunderstorm across central South Dakota. This storm pressed southeast producing copious amounts of wind-driven hail, then was followed by a more linear severe system a few hours later.
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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.
Winds backing ahead of a strong upper level wave along with approach of a upper level jet streak increased late-day shear and supported development of an initially isolated severe thunderstorm across central South Dakota. This storm pressed southeast producing copious amounts of wind-driven hail, then was followed by a more linear severe system a few hours later.
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 Jul 18, 11:11 AM CST, 2 hours 39 minutes earlier.
Area Forecast Discussion National Weather Service Sioux Falls SD 1211 PM CDT Wed Jul 18 2018 .SHORT TERM...(Today and Tonight) Issued at 411 AM CDT Wed Jul 18 2018 Main highlight of the entire forecast package is the widespread showers and thunderstorms expected by this evening. Wave digging into the high northern Plains seen on satellite water vapor imagery will continue translating eastward through the short term period, providing plenty of forcing for lift across the CWA by this afternoon. Still thinking the well advertised moderate rain forecast is on track, with most places receiving 0.5 to 1.5 inches, with locally higher amounts. PWAT values, while high, are not off the charts, but storm motion looks to be slow with Corfidi vectors and 0- 6 km mean flow both being less than 25 kts and generally getting slower as the upper wave pivots as it reaches the eastern Dakotas. Other concern in the short term is the potential for severe weather. There appears to be a small window in which storm redevelopment may occur in central SD before heading east-southeast into our southwestern CWA - mainly southwest of a 9V9-YKN line. Given the backed winds at the surface and the additional deep shear courtesy of the upper jet nosing into the region, could have a few hours with a threat for organized convection, and can't totally rule out an isolated tornado. As continued ascent leads to more widespread showers and storms by the evening, expect storms to agglomerate and the severe threat to diminish as the previously discussed heavy rain threat begins to ramp up. .LONG TERM...(Thursday through Tuesday) Issued at 411 AM CDT Wed Jul 18 2018 Long term period begins with the lingering effects of the upper wave on Thursday. Expect SW MN to be the cool spot as showers linger in the morning and skies slowly clear through the day. Meanwhile, south central SD will be sunny and could reach 90. Superblend actually did a decent job of illustrating this contrast in temperatures, so only had to tweak it a bit to get something realistic. The remainder of the extended features mostly benign weather. The upper low continues to build eastward into the Great Lakes for Friday, with a slight chance for showers and thunderstorms in our eastern CWA as a disturbance rounds the backside of this feature. Otherwise, a return to the nice weather appears to be in store for Saturday as ridging aloft builds in. A small disturbance rides the ridge on Sunday, so left in chance PoPs during this period. && .AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon) Issued at 1208 PM CDT Wed Jul 18 2018 Showers and thunderstorms will become more numerous west of Interstate 29 through the afternoon. The thunderstorm threat will then spread east towards Interstate 29, southwest MN and northwest IA during the evening and overnight hours. MVFR ceilings will become likely late tonight as the rainfall exits. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && SHORT TERM...Ferguson LONG TERM...Ferguson AVIATION...08
Hazardous Weather Outlook National Weather Service Sioux Falls SD 338 AM CDT Wed Jul 18 2018 NEZ013-014-SDZ050-057>060-063>065-068>070-190845- Dixon-Dakota-Gregory-Brule-Aurora-Davison-Hanson-Charles Mix- Douglas-Hutchinson-Bon Homme-Yankton-Clay SD- 338 AM CDT Wed Jul 18 2018 This Hazardous Weather Outlook is for portions of northeast Nebraska, south central South Dakota, and southeast South Dakota. .DAY ONE...Today and Tonight Severe thunderstorms are possible this afternoon with hail up to quarter size and wind gusts up to 60 mph being the main threats. Additionally, an isolated tornado cannot be ruled out. Furthermore, heavy rain may become an issue this afternoon through tonight due to expected slow movement of showers and thunderstorms. Expect half an inch to an inch and a half of rainfall with locally higher amounts possible. .DAYS TWO THROUGH SEVEN...Thursday through Tuesday Thursday through Tuesday look to be mostly uneventful, with Friday and Sunday having a slight chance for thunderstorms. At this time, any thunderstorms are not expected to be severe. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed between 1 pm and 7 pm this afternoon. IAZ001-012-020-031-SDZ038-039-052>055-061-062-066-067-071-190845- Lyon IA-Sioux-Plymouth-Woodbury-Beadle-Kingsbury-Jerauld-Sanborn- Miner-Lake-McCook-Minnehaha-Turner-Lincoln SD-Union- 338 AM CDT Wed Jul 18 2018 This Hazardous Weather Outlook is for portions of northwest Iowa, west central Iowa, central South Dakota, east central South Dakota, and southeast South Dakota. .DAY ONE...Today and Tonight Severe thunderstorms are possible this afternoon with hail up to quarter size and wind gusts up to 60 mph being the main threats. Furthermore, heavy rain may become an issue this afternoon through overnight tonight due to expected slow movement of showers and thunderstorms. Expect half an inch to an inch and a half of rainfall with locally higher amounts possible. .DAYS TWO THROUGH SEVEN...Thursday through Tuesday Thursday through Tuesday look to be mostly uneventful, with Friday and Sunday having a slight chance for thunderstorms. At this time, any thunderstorms are not expected to be severe. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed between 1 pm and 7 pm this afternoon. IAZ002-003-013-014-021-022-032-MNZ071-072-080-081-089-090-097-098- SDZ040-056-190845- Osceola-Dickinson-O'Brien-Clay IA-Cherokee-Buena Vista-Ida- Lincoln MN-Lyon MN-Murray-Cottonwood-Nobles-Jackson-Pipestone- Rock-Brookings-Moody- 338 AM CDT Wed Jul 18 2018 This Hazardous Weather Outlook is for portions of northwest Iowa, west central Iowa, southwest Minnesota, and east central South Dakota. .DAY ONE...Today and Tonight Heavy rain may become an issue this afternoon through overnight tonight due to expected slow movement of showers and thunderstorms. Expect half an inch to an inch and a half of rainfall with locally higher amounts possible. .DAYS TWO THROUGH SEVEN...Thursday through Tuesday Thursday through Tuesday look to be mostly uneventful, with Friday and Sunday having a slight chance for thunderstorms. At this time, any thunderstorms are not expected to be severe. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed today and tonight.
The Sioux Falls radar (KFSD), 178 km away, was scanning. The volume nearest the first event began at 19:49 UTC.
2 hail, 2 flash flood, 1 thunderstorm wind. Local standard time, as filed.
Wind gusts estimated from 40 to 50 mph preceded the hail. Hail occurred with very heavy rainfall.
Runoff from heavy rainfall caused flooding of several county roads.
Hail was very jagged, and hardly and liquid drops at all during hail fall.
Cars were stranded in foot deep waters on Broadway Street. Report received via social media.
Damage to trees and crops.
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, July 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 2026-10-01. Each event’s entry at NCEI: 773246, 773244, 773247, 773245, 773248.