A potent shortwave embedded in northwest flow moved across Iowa, providing a focus from storm development in an environment that already had MLCAPE values of 2500-3000 J/kg and effective bulk shear of around 40 knots. Convection that occurred earlier in the morning of July 11th also provided a focus for storm development on lingering outflow boundaries.
Every event with a place to put it. Tap one for its entry below.
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 DMX wrote it up.
A potent shortwave embedded in northwest flow moved across Iowa, providing a focus from storm development in an environment that already had MLCAPE values of 2500-3000 J/kg and effective bulk shear of around 40 knots. Convection that occurred earlier in the morning of July 11th also provided a focus for storm development on lingering outflow boundaries. This allowed for swaths of large hail across the state, with reports of up to tennis ball sized hail in some locations.
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 Des Moines, IA wrote its last area forecast discussion before the first event at Jul 11, 11:36 AM CST, 1 hour 9 minutes earlier.
Area Forecast Discussion National Weather Service Des Moines IA 1236 PM CDT Sat Jul 11 2020 ...Aviation Update... .DISCUSSION.../Today through Friday/ Issued at 403 AM CDT Sat Jul 11 2020 Today into this evening...A decent shortwave will drop out of the Northern Plains and across northeast Iowa. By mid to late afternoon, surface based CAPE increases to around 3000 J/Kg with pockets of shear in the 30-40kt range...especially over eastern Iowa. We will likely see scattered thunderstorm development with the shortwave coming in and given the shear, a few storms will likely produce large hail initially with locally damaging wind becoming the more dominant threat with time. DCAPE values from mid to late afternoon across the northeast range from 1000 J/Kg to a little over 1200 J/Kg before waning during the evening. For our area, the window for convection is fairly narrow...favored between 20Z and 01Z before pushing east. Later tonight through Monday night...Upper level ridging will be over the region so it will be dry with warm temps to start the week. On Tuesday, a shortwave breaks down the ridge and pushes the axis of the ridge to the east. AS the shortwave pushes east, much of the area will have precip chances beginning west and north Tuesday then spreading east and south Tuesday night and Wednesday. Wednesday night and Thursday we are in between systems thus dry but on the cool side. From Friday into next weekend, models are not in good agreement on the timing and placement is a warm front setting up but in any event, warming temps are expected late next week into the weekend. Right now we have 85 to 90 for highs Friday/Saturday but the potential for much hotter temps exists. The boundary location and storm development will have an impact but for now I kept the current trend of the going forecast. && .AVIATION.../For the 18Z TAFS through 18Z Sunday afternoon/ Issued at 1232 PM CDT Sat Jul 11 2020 Thunderstorm activity later this afternoon and evening most likely to affect KFOD/KMCW, with lesser chances to affect KFOD/KDSM/KOTM. As such, have entered periods of prevailing TSRA at KMCW/KALO with MVFR reductions this evening, and limited to VCTS or no mentions at KFOD/KDSM/KOTM and prevailing VFR. Otherwise, prevailing WNW/NW winds potentially gusting to around 25kts as deep mixing is achieved. && .DMX WATCHES/WARNINGS/ADVISORIES... NONE. && DISCUSSION...FAB AVIATION...Curtis
Hazardous Weather Outlook National Weather Service Des Moines IA 443 AM CDT Sat Jul 11 2020 IAZ006-007-016-017-025>028-036>039-048>050-061-062-075-086-097- 120945- Winnebago-Worth-Hancock-Cerro Gordo-Wright-Franklin-Butler-Bremer- Hamilton-Hardin-Grundy-Black Hawk-Story-Marshall-Tama-Jasper- Poweshiek-Mahaska-Wapello-Davis- 443 AM CDT Sat Jul 11 2020 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...Today and tonight Scattered severe thunderstorms are expected this afternoon and early evening. The main threats are damaging thunderstorm winds and large hail. .DAYS TWO THROUGH SEVEN...Sunday through Friday Thunderstorms are possible late Monday night through Wednesday over most of the area. Additional thunderstorms are possible Thursday and Friday. The severe weather potential for next week will be determined in the coming days. .SPOTTER INFORMATION STATEMENT... Spotters may be needed this afternoon and early evening. IAZ004-005-015-023-024-034-035-045>047-057>060-070>074-081>085- 092>096-120945- Emmet-Kossuth-Palo Alto-Pocahontas-Humboldt-Calhoun-Webster- Carroll-Greene-Boone-Audubon-Guthrie-Dallas-Polk-Cass-Adair- Madison-Warren-Marion-Adams-Union-Clarke-Lucas-Monroe-Taylor- Ringgold-Decatur-Wayne-Appanoose- 443 AM CDT Sat Jul 11 2020 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...Today and tonight Isolated strong to severe thunderstorms are possible this afternoon and early evening. The main threats are damaging thunderstorm winds and large hail. .DAYS TWO THROUGH SEVEN...Sunday through Friday Thunderstorms are possible late Monday night through Wednesday over most of the area. Additional thunderstorms are possible Thursday and Friday. The severe weather potential for next week will be determined in the coming days. .SPOTTER INFORMATION STATEMENT... Spotters may be needed this afternoon. IAZ033-044-120945- Sac-Crawford- 443 AM CDT Sat Jul 11 2020 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...Today and tonight Isolated to scattered non severe thunderstorms are possible this afternoon and evening. .DAYS TWO THROUGH SEVEN...Sunday through Friday Thunderstorms are possible late Monday night through Wednesday over most of the area. Additional thunderstorms are possible Thursday and Friday. The severe weather potential for next week will be determined in the coming days. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected today. REV
The Des Moines radar (KDMX), 127 km away, was scanning. The volume nearest the first event began at 18:45 UTC.
42 hail, 2 thunderstorm wind, 1 funnel cloud, 1 heavy rain. Local standard time, as filed.
Multiple reports via social media of a funnel cloud southeast of Pocahontas and southwest of Gilmore City.
Public report via social media of quarter sized hail.
A delayed report relayed via broadcast media of 2.5 inches of rain in Mason City ending at 3:23 pm. Begin time estimated via radar.
A trained spotter reported quarter sized hail on the northwest side of Fort Dodge.
A trained spotter reported golf ball sized hail.
A trained spotter reported ping pong ball sized hail near Fort Dodge.
A trained spotter reported quarter to golf ball sized hail southeast of Fort Dodge.
A social media picture showed damage to sweet corn east of Coalville. Possible that damage was due to a mix of hail and wind, which flattened the corn. Time estimated via radar.
A report relayed via KICD of golf ball sized hail. Time estimated via radar.
A report via social media of ping pong ball sized hail.
A report relayed via KICD of quarter sized hail.
A social media report of ping pong ball sized hail in Sheffield.
A public report of 2 inch hail.
KICD radio relayed a report of hail up to tennis ball size near Mallard. Time and location estimated via radar.
NWS employee reported quarter sized hail southwest of Clarksville.
Broadcast media relayed a report of ping pong ball sized hail just north of Hanlontown occurring around 3:30 pm.
A report via social media of tennis ball sized hail. Time and location estimated via radar.
A trained spotter reported quarter sized hail at the intersection of E18 and R38 northwest of Gilbert.
Law enforcement reported quarter to ping pong ball sized hail in Story City lasting 1 to 2 minutes.
KCCI replayed a report and picture of ping pong ball sized hail near Kanawha. Time estimated via radar.
Public report of ping pong ball sized hail.
KWWL relayed a report of 2 inch hail. Time and location estimated via radar.
KWWL relayed a report of quarter sized hail. Time and location estimated via radar.
The Mason City airport reported a wind gust of 54 knots.
KWWL relayed a report of nickel sized hail. Time and location estimated via radar.
A trained spotter reported quarter sized hail one mile north of Mason City.
KWWL relayed a report of quarter sized hail. Time and location estimated via radar.
A trained spotter reported quarter sized hail.
A public report of 1.25 inch hail was relayed to the office.
A trained spotter reported quarter sized hail.
A public report via social media of golf ball sized hail.
Emergency manager relayed a report of tennis ball sized hail at the intersection of 620th ave and 120th st in Story County.
KCCI relayed a report of tennis ball sized hail.
Emergency manager reported nickel to quarter sized hail.
Public report via social media of golf ball sized hail.
A trained spotter reported quarter sized hail on US 65 halfway between Colo and Zearing.
A trained spotter reported 1.25 inch hail 1 mile southwest of McCallsburg.
Law enforcement reported quarter sized hail in Nevada.
Emergency manager reported ping pong ball sized hail.
Emergency manager reported 2 inch hail.
A trained spotter reported 1.25 to 1.5 inch hail southeast of Colo.
A public report via social media of nickel sized hail.
The Baxter Fire Department reported quarter sized hail.
A trained spotter reported quarter sized hail 4 miles east of Newton.
A trained spotter reported penny sized hail.
A trained spotter reported quarter sized hail.
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, 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: 903275, 903276, 903292, 903277, 903278, 903280, 903281, 903282, 903285, 903286, 903287, 903288, 903293, 903295, 903296, 903297, 903298, 903300, 903302, 903303, 903304, 903305, 903306, 903307, 903308, 903309, 903310, 903311, 903312, 903313, 903315, 903317, 903318, 903319, 903320, 903321, 903323, 903324, 903325, 903326, and more.