A potent environment with 2500-3000 J/kg MLCAPE remained weakly capped until a wave moved across northern Nebraska by mid to late evening. Clusters of thunderstorms developed and organized into short bowing segments, which produced spotty damaging wind gusts.
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The episode as NWS FSD wrote it up.
A potent environment with 2500-3000 J/kg MLCAPE remained weakly capped until a wave moved across northern Nebraska by mid to late evening. Clusters of thunderstorms developed and organized into short bowing segments, which produced spotty damaging wind gusts.
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 8, 5:01 PM CST, 2 hours 59 minutes earlier.
AREA FORECAST DISCUSSION...UPDATED National Weather Service Sioux Falls SD 601 PM CDT Wed Jul 8 2020 .SHORT TERM...(This Evening through Thursday) Issued at 222 PM CDT Wed Jul 8 2020 Mid and upper level clouds across most of eastern SD with some clearing in central SD. This has allowed for some heating in central SD but temperatures still mostly upper 80s to lower 90s at 19z. The surface front was just west of the area. Latest HRRR starting to back off on the more widespread convection in the James Valley from about 22-01z and starting development a little later and mostly in south central SD. Thunderstorms do still expand northward after this but more in the 1-3z window. This seems to make some sense as the cap is fairly robust and the HRRR and RAP were both eroding the cap by what appears to be some sort of diurnal mixing of moisture upwards. This seems pretty likely, but not sure if the 6 to 10 degree C rises in dew point and a 2 degree C or so fall in temperature near 700 mb is plausible. There is no mid level moisture upstream at DDC or LBF. If the cap cannot break late this afternoon there does appear to be a wave moving into the panhandle of NE that could move into north central NE from roughly 0-3z and would kick start the convection. One other concern is the surface low to the northwest is steady state or filling a bit so the winds at the surface are not back and converging on the surface front but remaining southwest. Once the convection gets going suspect that anything that can develop north of I-90 will move northeast and dissipate shortly after sunset or become more organized north of our area. The activity in NE has a better chance of holding together into the later night hours and could bring a MCV into northwest IA Thursday morning. This would bring a chance for some isolated strong updrafts into IA on Thursday morning and early afternoon. As for the environment, if storms get going in central SD late this afternoon CAPE values are burly, around 2500 to 3000 J/kg with decent unidirectional shear. This might support a splitting supercell or two with left movers racing north northeast about 35 to 40 mph and right movers moving southeast about 15 to 20 mph. Low level inflow oriented from the south and southwest so in all likelihood storms will progress east and southeast for a time, then start to drop a little more due south as the new updrafts form and a possible cold pool starts to drive development. Later tonight it would mainly be a wind threat and this would likely be close to the Missouri River. .LONG TERM...(Thursday Night through Wednesday) Issued at 222 PM CDT Wed Jul 8 2020 On Thursday increased pops in northwest IA with concerns that the MCV will drift northeast and bring some showers and thunderstorms. The main concerns for this will likely be farther east but northwest IA should still see some activity. And once again a few stronger updrafts are possible with hail the main threat. Otherwise temperatures and humidity will be a bit more seasonal with highs in the 80s and dew points in the 60s. Thursday night should be quiet as upper level ridging spreads across the area. This will allow for quieter weather, lighter winds and Friday morning lows in the lower to mid 60s. Friday and especially Friday night have some red flags for severe weather potential. A fairly strong wave is expected to move onto the Western High Plains and into eastern SD, southwest MN and northwest IA by evening. Models very agreeable in producing a westerly upper level jet with winds averaging about 50 to 90 knots. This really cranks up the low and mid level wind field and in turn of course offers a significant increase in available shear. CAPE values appear as though they will be a bit lower, likely 1500 to 2000 J/kg. Would expect an environment like this to produce a larger scale bowing segment if model timing is correct. Saturday continues the trend of highs in the 80s as the main wave associated with this strong jet streak drops southeast. Will likely see some lingering showers and thunderstorms east of Interstate 29 but for now looks like a dry sounding so only small chances. Saturday night through Sunday night looks quiet with dry northwest flow aloft. There are hints that another fairly strong wave will move into the area on Monday but Monday through Wednesday far enough out to not really bite on anything other than what looks like a continued busy weather pattern with highs in the 80s to lower 90s. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 554 PM CDT Wed Jul 8 2020 Main impact this evening will be scattered thunderstorms developing along a weak cold front, likely remaining east of KHON/K9V9 and west of Interstate 29 early this evening. This activity will affect locations near KHON initially, then trek east overnight toward KFSD and KSUX with strong wind gusts, large hail, and heavy rain possible with the strongest storms this evening. Confidence is low as to whether storms will make it to KFSD and KSUX; could see storms, just rain, or just lower VFR ceilings, most likely from 04-08z near KFSD and 07z-11z at KSUX. Outside of storms, VFR conditions are expected. Gusty south winds should decrease after sunset, turning north behind the front overnight. Expect VFR conditions to prevail early Thursday. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...NONE. MN...NONE. IA...NONE. NE...NONE. && SHORT TERM...08 LONG TERM...08 AVIATION...BP
Hazardous Weather Outlook National Weather Service Sioux Falls SD 532 AM CDT Wed Jul 8 2020 IAZ001>003-012>014-020>022-031-032-MNZ081-089-090-NEZ013-014-SDZ071- 091045- Lyon-Osceola-Dickinson-Sioux-O'Brien-Clay-Plymouth-Cherokee- Buena Vista-Woodbury-Ida-Cottonwood-Nobles-Jackson-Dixon-Dakota- Union- 532 AM CDT Wed Jul 8 2020 This Hazardous Weather Outlook is for northwest Iowa, west central Iowa, southwest Minnesota, northeast Nebraska and southeast South Dakota. .DAY ONE...Today and tonight. Heat index values of 95 to 100 are expected this afternoon. Thunderstorms are possible this evening into the overnight hours. Some thunderstorms may produce hail to the size of nickels and wind gusts to 70 mph. .DAYS TWO THROUGH SEVEN...Thursday through Tuesday. Additional thunderstorms are possible Thursday morning. An isolated wind gust to 60 mph is possible. .SPOTTER INFORMATION STATEMENT... Spotter activation is possible after 8 pm tonight. MNZ071-072-080-097-098-SDZ038>040-050-052>070-091045- Lincoln-Lyon-Murray-Pipestone-Rock-Beadle-Kingsbury-Brookings- Gregory-Jerauld-Sanborn-Miner-Lake-Moody-Brule-Aurora-Davison-Hanson- McCook-Minnehaha-Charles Mix-Douglas-Hutchinson-Turner-Bon Homme- Yankton-Clay- 532 AM CDT Wed Jul 8 2020 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...Today and tonight. Heat index values of 95 to 100 are expected this afternoon. Thunderstorms are possible late this afternoon into this evening. Some thunderstorms may produce hail up to two inches in diameter and wind gusts to 75 mph. .DAYS TWO THROUGH SEVEN...Thursday through Tuesday. Additional thunderstorms are expected Friday night. These storms may produce large hail and damaging winds. .SPOTTER INFORMATION STATEMENT... Spotter activation is possible after 5 pm.
The Sioux Falls radar (KFSD), 160 km away, was scanning. The volume nearest the first event began at 02:02 UTC.
4 thunderstorm wind, 1 hail. Local standard time, as filed.
South Dakota RWIS station SD588 near Fort Randall Dam measured a wind gust to 68 mph.
Tree branches from 3 to 4 inches in diameter were taken down in the yard.
Strong winds displaced silo dump wagons.
Hail was mostly pea-sized with some up to the size of a penny, which was accompanied by winds to around 45 mph.
A couple limbs from 6 to 8 inches in diameter were taken down by thunderstorm wind gusts. Crop damage is an estimate from insured losses. Information provided by the United States Department of Agriculture.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in South Dakota in 2020Every state in 2020This day in weather historyWarnings in South Dakota, July 2020
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 2026-09-30. Each event’s entry at NCEI: 910158, 910152, 910160, 910148, 910154.