A pair of supercell storms developed on the southern periphery of a bowing system across northeast South Dakota and west central Minnesota within an environment with around 2000 J/kg MLCAPE and 40 knots of deep-layer shear.
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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.
A pair of supercell storms developed on the southern periphery of a bowing system across northeast South Dakota and west central Minnesota within an environment with around 2000 J/kg MLCAPE and 40 knots of deep-layer shear.
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 20, 5:27 PM CST, 3 hours 33 minutes earlier.
AREA FORECAST DISCUSSION National Weather Service Sioux Falls SD 627 PM CDT Mon Jul 20 2020 .SHORT TERM...(This Evening through Tuesday) Issued at 240 PM CDT Mon Jul 20 2020 Focus in the near term portions of the forecast revolve around thunderstorm chances late this afternoon into the evening, some of which may be severe. Have been watching an area of thunderstorms working thru western/central South Dakota thru much of the morning and early afternoon hours in response to ejecting mid level wave. Early afternoon mesoanalysis reveals a largely uncapped or weakly capped environment ahead of this complex characterized by MLCAPE values roughly between 1500-2000 J/kg. Some guidance would suggest this instability may peak at around 2500 J/kg later this afternoon. Additionally, 0-6 km shear values along and west of I-29 reside in the 40-45 kt range, buffered by 30 to 40 kts elsewhere. This would suggest support for maintenance of this cluster as it arrives into our western counties, likely between the 4-6 pm time frame. Forecast soundings from areas west of the James River advertise DCAPE values a couple hundred joules either side of 1000, and given the already upscale/bowing nature of the convection, would support the idea of damaging wind gusts up to 70 mph as the primary risk. If a stronger, and preferably more discrete, updraft can establish, hail to around the size of half dollars may materialize. Storms should outrun the better instability as they move east of the James River and thus would expect a weakening trend toward the I-29 corridor. Depending on any lingering showers/storm activity by the early morning/daybreak hours, could see some low clouds around and/or fog with a saturated boundary layer. Overnight lows in the lower to mid 60s are expected. Boundary will slowly sag south across NW IA Tuesday afternoon and with some remaining instability, could see a few showers or weak thunderstorms pop up near and ahead of it. Wouldn't expect any significant impacts from this activity however. Highs should be within a few degrees either side of today's values, generally upper 70s to mid 80s. .LONG TERM...(Tuesday Night through Monday) Issued at 240 PM CDT Mon Jul 20 2020 A rather muddled extended forecast in terms of precipitation chances with timing differences in the various models regarding disturbances working through the flow. First notable timeframe for perhaps a better focus for chances is Thursday morning with push of warm advection although differences exist in placement of better Theta-E push and low level jet convergence. Another wave lifts thru Thursday night and may provide for another period of enhanced POPs. Upper level ridge amplifies northward by Friday into the weekend which should result in a decrease in any thunderstorm activity, although our region remains close enough to its periphery to allow for some slight chances to remain. What is more certain is a warming trend thru the second half of the week. Temperatures at 850 mb warm back into the mid to upper 20s C which should push high temperatures into the 90s. This, combined with dewpoints back into the 70s, will once again bring heat concerns to the region. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 619 PM CDT Mon Jul 20 2020 Weakening line of thunderstorms moving east along the highway 14 corridor this evening. Could see visibilities briefly reduced to 3 miles in heavier rain. Convective chances this evening are really uncertain. Weak forcing could lead to isolated - scattered activity along and west of the James River. As the evening progresses, could see additional chances for thunderstorms along and east of I-29 after 06Z Tuesday as weak low level warm air advection develops. Confidence in coverage and precise location is not high enough at this point to mention in the TAFs. Models are also hinting at lower MVFR ceilings/fog towards 12Z Tuesday east of I-29. Confidence is low enough at this time to not include a mention in the forecast, but will take a second look at this for the 06Z issuance. If lower ceilings develop Tuesday morning, they are expected to gradually raise through the day giving way to VFR. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...NONE. MN...NONE. IA...NONE. NE...NONE. && SHORT TERM...Kalin LONG TERM...Kalin AVIATION...BT
Hazardous Weather Outlook National Weather Service Sioux Falls SD 1227 PM CDT Mon Jul 20 2020 SDZ038-039-050-052>054-057>060-063>065-068-211730- Beadle-Kingsbury-Gregory-Jerauld-Sanborn-Miner-Brule-Aurora-Davison- Hanson-Charles Mix-Douglas-Hutchinson-Bon Homme- 1227 PM CDT Mon Jul 20 2020 This Hazardous Weather Outlook is for central South Dakota, east central South Dakota, south central South Dakota and southeast South Dakota. .DAY ONE...This afternoon and tonight. Isolated to scattered thunderstorms are possible from late afternoon thru the evening hours, some of which may be severe. Large hail to the size of half dollars and damaging wind gusts up to 70 mph are possible beneath the strongest storms. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday. Hazardous mid-summer heat is likely Friday and into the weekend, with heat index values above 100. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed after 4 pm this afternoon and evening. IAZ001>003-012>014-020>022-031-032-MNZ071-072-080-081-089-090-097- 098-NEZ013-014-SDZ040-055-056-061-062-066-067-069>071-211730- Lyon-Osceola-Dickinson-Sioux-O'Brien-Clay-Plymouth-Cherokee- Buena Vista-Woodbury-Ida-Lincoln-Murray-Cottonwood-Nobles-Jackson- Pipestone-Rock-Dixon-Dakota-Brookings-Lake-Moody-McCook-Minnehaha- Turner-Yankton-Union- 1227 PM CDT Mon Jul 20 2020 This Hazardous Weather Outlook is for northwest Iowa, west central Iowa, southwest Minnesota, northeast Nebraska, east central South Dakota and southeast South Dakota. .DAY ONE...This afternoon and tonight. Isolated thunderstorms are possible this evening and into the early overnight hours, with a small chance for hail and strong wind gusts beneath the strongest storms. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday. Hazardous mid-summer heat is likely Friday and into the weekend, with heat index values above 100. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time.
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
757 PM CDT MON JUL 20 2020
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0740 PM TSTM WND DMG 11 N COLMAN 44.14N 96.80W
07/20/2020 MOODY SD TRAINED SPOTTER
LARGE TREE BRANCHES BLOWN DOWN. ALSO DIME
SIZED HAIL.
&&
TRMPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
807 PM CDT MON JUL 20 2020
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0759 PM TSTM WND GST 10 SSW AURORA 44.15N 96.76W
07/20/2020 M60 MPH MOODY SD MESONET
MESONET STATION 224 SD RWIS WARD.
&&
TRMPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
914 PM CDT MON JUL 20 2020
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0740 PM HEAVY RAIN NUNDA 44.16N 97.01W
07/20/2020 M1.32 INCH LAKE SD PUBLIC
TWIGS WERE ALSO BLOWN DOWN BY THUNDERSTORM
WIND GUSTS.
&&
TRMPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
915 PM CDT MON JUL 20 2020
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0901 PM HEAVY RAIN 6 E FLANDREAU 44.06N 96.49W
07/20/2020 M1.24 INCH MOODY SD CO-OP OBSERVER
CO-OP OBSERVER STATION FCRS2 6.6 S WARD.
&&
TRMPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
916 PM CDT MON JUL 20 2020
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0908 PM HEAVY RAIN VOLGA 44.32N 96.92W
07/20/2020 M1.67 INCH BROOKINGS SD MESONET
MESONET STATION AT197 VOLGA.
&&
TRMPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
934 PM CDT MON JUL 20 2020
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0853 PM HEAVY RAIN FLANDREAU 44.05N 96.59W
07/20/2020 M1.24 INCH MOODY SD CO-OP OBSERVER
HEAVY RAINFALL IN A SHORT PERIOD OF TIME.
&&
TRMThe Sioux Falls radar (KFSD), 70 km away, was scanning. The volume nearest the first event began at 02:58 UTC.
1 thunderstorm wind, 1 hail. Local standard time, as filed.
Half of a twenty year old apple tree was broken off by strong winds. 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 Minnesota in 2020Every state in 2020This day in weather historyWarnings in Minnesota, 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 2026-09-24. Each event’s entry at NCEI: 910388, 910386.