A cold front pushed into a volatile airmass across northwest Iowa and southwest Minnesota by late afternoon with up to 3000 J/kg MLCAPE. Scattered thunderstorms erupted with stronger storms producing large hail.
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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 cold front pushed into a volatile airmass across northwest Iowa and southwest Minnesota by late afternoon with up to 3000 J/kg MLCAPE. Scattered thunderstorms erupted with stronger storms producing large hail.
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 14, 11:44 AM CST, 2 hours 10 minutes earlier.
AREA FORECAST DISCUSSION National Weather Service Sioux Falls SD 1244 PM CDT Fri Aug 14 2020 .UPDATE... Issued at 944 AM CDT Fri Aug 14 2020 Cold front is beginning to work into the western portion of the forecast area, noted by the wind shift to the northwest from the south at K9V9 and points westward. Satellite shows low clouds in this area as well, with temperatures at K9V9 and KPIR in the mid to upper 60s. Ahead of the front, temps remain the mid and upper 70s (with KFSD up to 81). Showers and isolated lightning strikes have developed in south central SD and northeastern NE. However, this activity has been diminishing over the last 15 minutes or so as it moves east. Otherwise, previous discussion and thoughts remain on track in regards to this afternoon/evening severe weather potential. && .SHORT TERM...(Today and Tonight) Issued at 255 AM CDT Fri Aug 14 2020 A rather warm and breezy overnight continues as temperatures struggle to fall into the middle 70s in many areas. We're beginning to see a bit of cloud cover develop as the low-lvl jet increases. It's possible to see a few showers develop across portions of SW Minnesota through daybreak. Convective cluster along the ND/SD border will continue to move east to northeast through daybreak, with the southern cells riding along the northern fringes of the +13C line at 700 mb. Convective chances later today will be driven by an advancing cold front moving southeast by the mid-day hours. Ahead of this boundary, guidance continues to suggest MLCAPE values AOA 2500-3000 J/KG, with the front reaching the I-29 corridor early this afternoon. Scattered convection may begin to develop down the boundary as it slides into Minnesota and Iowa in the afternoon. Decent mid-lvl lapse rates and sufficient shear should support a severe weather risk as storms move eastward. Soundings suggest 2"+ hail potential, with mid-lvl dry air intrusion and unidirectional wind profile suggesting localized damaging wind gusts. The tornadic risk can't be discounted, but would like to see surface winds ahead of the boundary backed a bit more. Any tornadic threat may have to be enhanced by local or remnant outflow boundaries. The drawback for convection will be departing (and shearing) upper forcing and a stubborn warm layer aloft that could really limit upscale growth and coverage of storms. The area with the highest potential for development will be in SW Minnesota where PVA is maximized. The front will zip southeast quickly, moving away from the forecast area by 00z, and allowing a lower dew point airmass to advect into the area. Temperatures fall into the lower 50s by daybreak Saturday. .LONG TERM...(Saturday through Thursday) Issued at 255 AM CDT Fri Aug 14 2020 This weekend: The majority of the weekend will feature dry conditions. Temperatures on Saturday have been raised a bit in most areas, but especially west of the James River. Models showing a favorable warm advection pattern aloft, and when combined with a light southwest to west wind, and dry surface conditions, this should allow for guidance to edge towards the upper percentile ranges. Light winds could lead to a bit of valley fog Sunday morning. Models showing a minor shortwave moving through the region on Sunday. Minimal impacts are anticipated, but could see mid-lvl clouds and a bit of virga during the day. Next week: Mid-lvl heights rise over the western United States next week, and should bring mostly dry conditions to the region. Only minor risk of rain in the forecast appears to be focused in the Wednesday time frame when a subtle shortwave tops the upper ridge. Temperatures will hover near to slightly above the seasonal normals. && .AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon) Issued at 1231 PM CDT Fri Aug 14 2020 Cold front is working across the area through mid-evening. Ahead of the front, southerly winds are gusting up to 30 knots with low VFR conditions. MVFR conditions are occurring for about an hour as the front passes. Current showers/isolated thunderstorms will increase in coverage along/near the front as it approaches/passes I-29. Greatest shower/storm chances are mid- afternoon across southwestern MN and northwestern IA. After the front passes, winds shift to the northwest with gusts up to 30 knots possible through sunset. Skies clear behind the front with VFR conditions. Expect winds overnight to be light and variable. Patchy fog is possible, especially in low-lying areas. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...NONE. MN...NONE. IA...NONE. NE...NONE. && UPDATE...SG SHORT TERM...Dux LONG TERM...Dux AVIATION...SG
Hazardous Weather Outlook National Weather Service Sioux Falls SD 439 AM CDT Fri Aug 14 2020 IAZ001>003-012>014-020>022-031-032-MNZ072-080-081-089-090-098- NEZ013-014-SDZ071-150945- Lyon-Osceola-Dickinson-Sioux-O'Brien-Clay-Plymouth-Cherokee- Buena Vista-Woodbury-Ida-Murray-Cottonwood-Nobles-Jackson-Rock- Dixon-Dakota-Union- 439 AM CDT Fri Aug 14 2020 This Hazardous Weather Outlook is for portions of northwest Iowa, west central Iowa, southwest Minnesota, northeast Nebraska, and southeast South Dakota. .DAY ONE...Today and Tonight A cold front will move into the outlook area by mid-afternoon Friday. Scattered thunderstorms may develop along this boundary between 2pm and 7pm. A few strong to severe storms will be possible across southwest Minnesota and northwest Iowa. Storms may bring the risk for 2 inch hail and 70 mph winds. The tornado risk remains very low. .DAYS TWO THROUGH SEVEN...Saturday through Thursday No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed between 2pm and 7pm Friday. MNZ071-097-SDZ038>040-050-052>070-150945- Lincoln-Pipestone-Beadle-Kingsbury-Brookings-Gregory-Jerauld- Sanborn-Miner-Lake-Moody-Brule-Aurora-Davison-Hanson-McCook- Minnehaha-Charles Mix-Douglas-Hutchinson-Turner-Bon Homme-Yankton- Clay- 439 AM CDT Fri Aug 14 2020 This Hazardous Weather Outlook is for portions of southwest Minnesota, central South Dakota, east central South Dakota, south central South Dakota, and southeast South Dakota. .DAY ONE...Today and Tonight A fast moving cold front will move through Friday afternoon. The greatest risk for thunderstorm development will be along and east of Interstate 29, briefly during early Friday afternoon. These developing storms could bring a risk of quarter size hail and 50 mph winds. The greater risks for severe storms will be focused east of Interstate 29 across southwest Minnesota and northwest Iowa. .DAYS TWO THROUGH SEVEN...Saturday through Thursday No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation is not anticipated.
The Sioux Falls radar (KFSD), 97 km away, was scanning. The volume nearest the first event began at 19:53 UTC.
4 hail. Local standard time, as filed.
Hail was mostly dime to nickel size, but some stones were as large as quarters.
Hail occurred near the intersection of county roads K18 and C43.
Pea to penny size hail fell with little wind.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2020Every state in 2020This day in weather historyWarnings in Iowa, August 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: 915215, 915218, 915220, 915221.