A narrow zone of enhanced instability developed ahead of a cold front with up to 1500-2000 J/kg MLCAPE. As a mid-level jet streak crossed the boundary in the late afternoon and evening, deep layer shear increased to around 50 knots.
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The episode as NWS FSD wrote it up.
A narrow zone of enhanced instability developed ahead of a cold front with up to 1500-2000 J/kg MLCAPE. As a mid-level jet streak crossed the boundary in the late afternoon and evening, deep layer shear increased to around 50 knots. Isolated thunderstorms developed supercell characteristics, resulting in large hail and damaging wind.
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 22, 5:08 PM CST, 27 minutes earlier.
AREA FORECAST DISCUSSION National Weather Service Sioux Falls SD 608 PM CDT Sun Aug 22 2021 .SHORT TERM...(This Evening through Monday) Issued at 242 PM CDT Sun Aug 22 2021 A fair amount to talk about over the next several days with the most immediate concern revolving around and severe chances later this afternoon and evening. Morning WAA driven elevated convection continues to lift off to the north and east and has occasionally produced small hail. As of early afternoon, a surface low is deepening across northeast ND with an attendant cold front east of a Faith to Phillip, SD. Subjective analysis would place a warm front between Winner and Chamberlain, arcing northeastward from there, perhaps transitioning to an occluded front toward ND. Visible satellite is largely void of any established Cu field yet, although perhaps the first signs of such a field near and south of Pierre. As we move into the late afternoon and early evening hours, forcing for ascent from pronounced wave noted on WV satellite over the Black Hills should begin to increase with at least isolated to scattered convection advertised from the various high-res CAM solutions. Guidance suggest solar insolation will have resulted in a narrow corridor of MLCAPE values roughly around 1000-1500 J/kg near the Hwy 14 corridor to perhaps as much as 2000 J/kg further south toward the MO River. A 500 mb jet max overspreading the area will push deep layer effective shear values in excess of 50 kts. Within this broader characterized environment, perhaps a couple of smaller differing environment will evolve. An area north of I-90 and a few counties either side of the James River Valley will see weaker instability however the potential for better backed surface winds may allow for more curvature of the low level hodograph and higher supercell potential. This area will also reside closer to the mid-level wave gliding off to the northeast and thus may stand a better chance at CI. While LCL heights likely sit above the preferred values, some hint in the guidance that localized pockets of BL moistening from morning convection may drive these values to more favorable values. This may allow for a spatially and temporally narrow window for a tornado or two in addition to a large hail and damaging wind threat. The second region south of I-90 and a few counties either side of the James River will see better moisture return/earlier clearing and thus higher instability but further away from the more robust upper level forcing. Should storms develop, elongated but fairly straight hodographs may allow for splitting supercells with large hail and damaging wind the primary threats. Should enough of a cold pool become established, 0-3 km shear vectors would allow for some organization of one or more eastward propagating line of storms. This solution is advertised in both the nested-NAM and NSSL WRF although there is lower confidence in this solution occurring. Any convection that does develop should fade in intensity by the late evening hours as upper level support peels north and diurnal heating is lost. Diminishing winds and clearing skies may allow for fog formation into the daybreak hours Monday. Latest guidance hangs up the west to east boundary across our coverage area for Monday with some disagreement on how far north/south this occurs. South of this baroclinic zone, both the deterministic NAM and GFS try to heat temperatures toward the upper 90s to near 100 (with the NAM maintaining higher Tds as well) but lacks much support from ensemble members other short range guidance. With this, both are fairly aggressive with afternoon instability and convective coverage which may be overdone given the rather subtle forcing from the weak incoming wave. Deep layer shear also not nearly as strong as today although still may see some values in the 30-40 kt range which is enough to introduce some severe potential and a Marginal from SPC. .LONG TERM...(Monday Night through Sunday) Issued at 242 PM CDT Sun Aug 22 2021 A rather messy and uncertain forecast for the remainder of the week as broad southwest flow aloft overspreads the Northern Plains with several embedded shortwaves/impulses. This will leave a multitude of convection chances in the forecast and while the populated NBM POPs are likely not nearly temporally focused enough, uncertainty precludes much improvement over this method at this time. Temperatures at 850 mb push into the 90th percentile of climatology and will set up another warm day for Tuesday, particularly south of I-90. For midweek and beyond, there remains a large degree of uncertainty as to boundary location and any convective debris and thus the temperature forecast becomes much more muddled. Ensemble means would suggest 80s should be fairly common. && .AVIATION...(For the 00Z TAFS through 00Z Monday evening) Issued at 604 PM CDT Sun Aug 22 2021 Main aviation concern in the near term is ongoing convection across central SD and exiting convection across SW MN. The former looks to stay south of KHON but will continue to monitor for future development. Will also need to monitor for convection to work toward KFSD in the mid to late evening hours. Have included VCTS mention for both of these threats. After convection diminishes overnight, may see fog develop toward the daybreak hours Monday morning with KHON and perhaps KFSD standing the highest chances of vsby restrictions. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...NONE. MN...NONE. IA...NONE. NE...NONE. && SHORT TERM...Kalin LONG TERM...Kalin AVIATION...Kalin
Hazardous Weather Outlook National Weather Service Sioux Falls SD 354 PM CDT Sun Aug 22 2021 SDZ050-057>061-063>065-068-232100- Gregory-Brule-Aurora-Davison-Hanson-McCook-Charles Mix-Douglas- Hutchinson-Bon Homme- 354 PM CDT Sun Aug 22 2021 This Hazardous Weather Outlook is for south central South Dakota and southeast South Dakota. .DAY ONE...This afternoon and tonight. Isolated to scattered storms are expected to develop late this afternoon, with some severe storms possible into this evening. Hail to golf ball size and damaging winds are the primary threats, with a low chance of a tornado. .DAYS TWO THROUGH SEVEN...Monday through Saturday. Periodic thunderstorm chances continue into the upcoming work week, perhaps as early as Monday evening. The chance for widespread severe weather appears low through the first half of the week but isolated strong to severe storms may be possible. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed late this afternoon and evening. SDZ038>040-052>056-232100- Beadle-Kingsbury-Brookings-Jerauld-Sanborn-Miner-Lake-Moody- 354 PM CDT Sun Aug 22 2021 This Hazardous Weather Outlook is for central South Dakota and east central South Dakota. .DAY ONE...This afternoon and tonight. Isolated to scattered storms are expected to develop late this afternoon, with some severe storms possible into this evening. Hail to golf ball size and damaging winds are the primary threats, with a low chance of a tornado. .DAYS TWO THROUGH SEVEN...Monday through Saturday. Periodic thunderstorm chances continue into the upcoming work week, perhaps as early as Monday evening. The chance for widespread severe weather appears low through the first half of the week but isolated strong to severe storms may be possible. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed late this afternoon and evening. IAZ001>003-012>014-020>022-031-032-MNZ071-072-080-081-089-090-097- 098-NEZ013-014-SDZ062-066-067-069>071-232100- Lyon-Osceola-Dickinson-Sioux-O'Brien-Clay-Plymouth-Cherokee- Buena Vista-Woodbury-Ida-Lincoln-Murray-Cottonwood-Nobles-Jackson- Pipestone-Rock-Dixon-Dakota-Minnehaha-Turner-Yankton-Union- 354 PM CDT Sun Aug 22 2021 This Hazardous Weather Outlook is for northwest Iowa, west central Iowa, southwest Minnesota, northeast Nebraska and southeast South Dakota. .DAY ONE...This afternoon and tonight. Isolated to scattered storms are possible later this evening and early overnight. A few storms may be strong to severe, with hail to half dollar size, and damaging wind gusts possible. .DAYS TWO THROUGH SEVEN...Monday through Saturday. Periodic thunderstorm chances continue into the upcoming work week, perhaps as early as Monday evening. The chance for widespread severe weather appears low through the first half of the week but isolated strong to severe storms may be possible. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time.
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
445 PM CDT SUN AUG 22 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0415 PM HAIL 6 SSE LUVERNE 43.57N 96.16W
08/22/2021 E1.00 INCH ROCK MN TRAINED SPOTTER
&&
SSCThe Sioux Falls radar (KFSD), 146 km away, was scanning. The volume nearest the first event began at 23:37 UTC.
3 hail, 1 thunderstorm wind. Local standard time, as filed.
Crop damage is an estimate from insured losses. Information provided by the United States Department of Agriculture.
County Emergency Manager estimated wind gusts as high as 80 to 90 mph.
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, August 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: 982268, 982269, 982271, 982272.