An isolated thunderstorm within an environment with a well-defined inverted-V sounding produced a downburst wind gust.
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The episode as NWS FSD wrote it up.
An isolated thunderstorm within an environment with a well-defined inverted-V sounding produced a downburst wind gust.
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 23, 5:36 PM CST, 2 hours 10 minutes earlier.
AREA FORECAST DISCUSSION National Weather Service Sioux Falls SD 636 PM CDT Fri Jul 23 2021 .SHORT TERM...(This Evening through Saturday) Issued at 258 PM CDT Fri Jul 23 2021 Surface dewpoints have not mixed out nearly as much as expected with many 23.19Z values in the lower to mid 70s. At the same time, temperatures have not been as high either and some cloud cover mainly north of I-90 has kept them in check. Taken together, still expect a few spots to top 100 degree heat indices this afternoon for a few hours, especially for areas with more sun from the SD/NE border region into northwest IA. Isolated nature of highest heat index values precludes issuance of a late Heat Advisory. Attention then turns to thunderstorm/severe potential this evening into the early overnight hours. Latest water vapor loop shows a subtle weak wave across WY and this feature is expected to drift across SD tonight. With steepening low-level lapse rates and elevated CAPE values up to 1500 J/kg, expect to see some convective development around 00Z across central SD and then move eastward into the forecast area this evening. Deep dry sub-cloud layer with inverted-V sounding and DCAPE to around 1000 J/kg suggests highest threat will be strong downburst wind up to 70 mph. Could still see some hail up to the size of quarters with the strongest updrafts. Thunderstorms should weaken with eastward progress and eventually move out of the forecast area by daybreak Saturday. All of this is covered well in the latest SPC Day 1 Convective Outlook, showing a slight risk for areas mainly west of a line from Brookings to Platte, SD. A dry cold front sweeps south Saturday, ushering in much drier near surface air. So much so that dewpoints should drop into the 50s north of I-90 and 60s to the south by late afternoon. Temperatures are still likely to rise into the lower 90s, but with drier air, heat index values will remain below 100 degrees and no advisory is expected. Otherwise, Saturday will see mostly sunny skies with light northerly breezes. .LONG TERM...(Saturday Night through Friday) Issued at 258 PM CDT Fri Jul 23 2021 Sunday into next week, massive 500 hPa ridge reasserts itself across the western CONUS with its axis along the spine of the Rockies. This puts the forecast area in northwest flow aloft along the periphery of the ridge. A few weak ripples in the flow could produce periodic convective clusters with the best chances Sunday night and again Wednesday night. Too early to determine timing, coverage, and potential severity, but something to watch over the coming days. All said, no widespread rains on the horizon and most locations will continue to see a lack of precipitation through next week. Of greater concern will be temperatures by Tuesday/Wednesday as aforementioned ridge builds eastward. It's looking more likely that air temperatures will top 100 degrees for many areas, especially along and west of the I-29 corridor. Dewpoints in the 60s will allow heat indices to top 100 degrees for many locations, so expect that Heat Advisories will eventually be needed. Temperatures decrease some by week's end as the ridge retreats westward in response to a southward moving trough across Hudson Bay into the eastern CONUS. && .AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon) Issued at 1245 PM CDT Fri Jul 23 2021 Scattered showers and isolated thunderstorms will be moving through the area this evening, likely exiting off into south central MN and north central IA by the early morning hours. The strongest storms could produce quarter-sized hail and wind gusts up to 70 mph, though the probability that it would affect any of the TAF sites remains low. Otherwise, a front will be moving through the area overnight, causing winds to be coming out of the north by the early-mid morning hours on Saturday. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...NONE. MN...NONE. IA...NONE. NE...NONE. && SHORT TERM...Rogers LONG TERM...Rogers AVIATION...Rogers
Hazardous Weather Outlook National Weather Service Sioux Falls SD 648 PM CDT Fri Jul 23 2021 MNZ071-072-080-097-SDZ038>040-050-052>065-250000- Lincoln-Lyon-Murray-Pipestone-Beadle-Kingsbury-Brookings-Gregory- Jerauld-Sanborn-Miner-Lake-Moody-Brule-Aurora-Davison-Hanson-McCook- Minnehaha-Charles Mix-Douglas-Hutchinson- 648 PM CDT Fri Jul 23 2021 This Hazardous Weather Outlook is for southwest Minnesota, central South Dakota, east central South Dakota, south central South Dakota and southeast South Dakota. .DAY ONE...Tonight. Scattered showers and isolated thunderstorms will be moving through the area this evening, with the strongest storms capable of producing quarter-sized hail and wind gusts up to 70 mph. The main time-frame where these stronger storms will be possible will be from 7 pm through midnight, with weaker storms expected after that. .DAYS TWO THROUGH SEVEN...Saturday through Thursday. Above normal temperatures will continue into next week. Those with outdoor activities are encouraged to keep heat safety in mind. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed. IAZ001>003-012>014-020>022-031-032-MNZ081-089-090-098-NEZ013-014- SDZ066>071-250000- Lyon-Osceola-Dickinson-Sioux-O'Brien-Clay-Plymouth-Cherokee- Buena Vista-Woodbury-Ida-Cottonwood-Nobles-Jackson-Rock-Dixon-Dakota- Turner-Lincoln-Bon Homme-Yankton-Union- 648 PM CDT Fri Jul 23 2021 This Hazardous Weather Outlook is for northwest Iowa, west central Iowa, southwest Minnesota, northeast Nebraska and southeast South Dakota. .DAY ONE...Tonight. Scattered showers and isolated thunderstorms will be moving through the area this evening into the early morning hours, though the probability of severe weather is low. .DAYS TWO THROUGH SEVEN...Saturday through Thursday. Above normal temperatures will continue into next week. Those with outdoor activities are encouraged to keep heat safety in mind. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time.
The Aberdeen radar (KABR), 126 km away, was scanning. The volume nearest the first event began at 01:44 UTC.
1 thunderstorm wind. Local standard time, as filed.
Thunderstorm wind gust was measured by South Dakota RWIS near Cavour.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in South Dakota in 2021Every state in 2021This day in weather historyWarnings in South Dakota, July 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: 977459.