A number of low level jet induced storms fired up along a warm front in eastern North Dakota and northeast South Dakota during the overnight hours of the 9th into the 10th. The overall environment was not substantial, but was conducive for storms.
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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 DMX wrote it up.
A number of low level jet induced storms fired up along a warm front in eastern North Dakota and northeast South Dakota during the overnight hours of the 9th into the 10th. The overall environment was not substantial, but was conducive for storms. MUCAPE values overnight were around the 1000 to 2000 J/kg range in the Dakotas along with a tight gradient of 30 to 50 kt effective shear values near and along the frontal boundary. The storms moved relatively equal to the mean wind direction, to the southeast or south southeast through the night. As the sun rose, storms were in southwest Minnesota and continuing to move towards Iowa. Storms continued to follow an increasing CAPE gradient down into Iowa, even as effective shear waned. For the most part, one lone strong to severe storm survived and produced reports of 50 to 60 mph winds and subsequent tree damage.
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 10, 5:28 AM CST, 5 hours 22 minutes earlier.
Area Forecast Discussion National Weather Service Des Moines IA 628 AM CDT Tue Jul 10 2018 .SHORT TERM.../Today through Tonight/ Issued at 325 AM CDT Tue Jul 10 2018 Weak surface boundary has made it to the I80 corridor early this morning. Some drier air has begun to enter far northern Iowa, otherwise little difference is noted on either side of the front other than the wind shift. The slightly cooler airmass will ease across the northeast half of the forecast area today with some minor relief to highs today along with slightly lower dewpoints. Farther to the south and west, temperatures and dewpoints will be similar to Monday and anticipate heat index values in the mid 90s again today across the southwest third of so of the forecast area. Other concern is some of the CAMs bring the convection across North Dakota close to the northeast corner of the forecast area toward midday on leading edge of moisture gradient. While the mention of storms have been left out of the forecast in those locations, near term trends will need to be monitored closely for the eventual evolution of these storms. For tonight, the best forcing and low level moisture transport remains well west and north of the forecast area. Western and southern areas will be the warmest where higher dewpoints and proximity to the thermal ridge will keep readings higher. More pleasant conditions are forecast to remain in the northeast where slightly lower dewpoints/temps will persist into tonight. .LONG TERM.../Wednesday through Monday/ Issued at 325 AM CDT Tue Jul 10 2018 Upper level ridging will continue to be over the area on Wednesday with surface high pressure over the Great Lakes. This will allow for a return to southerly flow that will promote another very warm day with a bit of a bump upwards in humidity. High temperatures will be 4 to 5 degrees above normal with heat index values in the 90s. As an area of low pressure tracks across the Canadian prairies with a cold front trailing to the south over the northern states, the upper level ridge will weaken. The front will lose its upper level support later on Thursday leaving this boundary as a focus for showers and storms. Clouds will increase Wednesday night with chances of rain and storms increasing on Thursday. As has been noted in previous discussions, the severe potential is less than the locally heavy rain potential at this point. The limiting factor to the severe is the lack of robust shear with the boundary being over southern Minnesota at peak heating with strong instability. Focus for any severe threat will be damaging wind gusts with isolated large hail given the shear parameters. The greater concern will be Thursday night as the boundary slowly moves into northern Iowa where the atmosphere will be moisture laden. Precipitable water values will be above normal with the 9/12z NAEFS specific humidity values in the 90th or higher percentile over the area. Warm cloud depths will be greater than 13000 feet with warm rain processes dominating. While mean flow will be 20 to 30 knots, the flow will be largely parallel to the boundary indicating a possibilitiy of training storms. Latest WPC outlook highlights northern Iowa with a marginal risk of excessive rainfall for this reason. While there will be breaks in the rainfall, the overall set up for the possibility of locally heavy rainfall will persist into Friday and may linger into Saturday as the boundary sinks farther south into the state with perhaps weaker mean flow these two days. A new area of low pressure will move across the Canadian prairies bringing a cold front into the state either late Sunday or more likely Monday. This would bring a round of showers and strong storms across central Iowa. The GFS continues to be the more progressive solution driving the front into Missouri with chances for showers and storms ending by early next week. Meanwhile, the ECMWF keeps storm chances as it is the slower and less progressive solution. At this time range, will stick with the initial blended guidance for Monday into early next week. && .AVIATION.../For the 12Z TAFS through 12Z Wednesday morning/ Issued at 628 AM CDT Tue Jul 10 2018 Widespread VFR conditions for much of the period with some scattered cumulus today as well as high cirrus drifting overhead. Surface winds will be light and eventually swinging around to the east southeast tonight. && .DMX WATCHES/WARNINGS/ADVISORIES...NONE. && SHORT TERM...Cogil LONG TERM...Ansorge AVIATION...Cogil
Hazardous Weather Outlook National Weather Service Des Moines IA 959 AM CDT Tue Jul 10 2018 IAZ004>007-015>017-023-024-111500- Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo- Pocahontas-Humboldt- 959 AM CDT Tue Jul 10 2018 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...Today and tonight Thunderstorms will track through north central Iowa this morning and into early afternoon. Severe weather threat is low, but small hail and gusty winds are possible. River Flood Warnings are in effect for parts of the Des Moines River basin. Please refer to the National Weather Service website at weather.gov/desmoines for further details. .DAYS TWO THROUGH SEVEN...Wednesday through Monday River Flood Warnings will remain in effect for parts of the Des Moines River basin likely into the first part of this weekend. Please refer to the National Weather Service website at weather.gov/desmoines for further details. Thunderstorm chances will increase Thursday into Friday lingering into this weekend. There is a risk of strong to severe storms over northern Iowa later Thursday with the main threats being damaging wind gusts, locally heavy rainfall, and large hail. The risk for locally heavy rain will remain possible on Friday. .SPOTTER INFORMATION STATEMENT... Spotters activation is not needed at this time. IAZ025>028-033>039-044>050-057>062-070>075-081>086-092>097-111500- Wright-Franklin-Butler-Bremer-Sac-Calhoun-Webster-Hamilton-Hardin- Grundy-Black Hawk-Crawford-Carroll-Greene-Boone-Story-Marshall- Tama-Audubon-Guthrie-Dallas-Polk-Jasper-Poweshiek-Cass-Adair- Madison-Warren-Marion-Mahaska-Adams-Union-Clarke-Lucas-Monroe- Wapello-Taylor-Ringgold-Decatur-Wayne-Appanoose-Davis- 959 AM CDT Tue Jul 10 2018 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...Today and tonight No hazardous weather is expected at this time. .DAYS TWO THROUGH SEVEN...Wednesday through Monday Thunderstorm chances will increase Thursday into Friday lingering into this weekend. There is a risk of strong to severe storms over northern Iowa later Thursday with the main threats being damaging wind gusts, locally heavy rainfall, and large hail. The risk for locally heavy rain will remain possible on Friday. .SPOTTER INFORMATION STATEMENT... Spotters activation is not needed at this time.
The Des Moines radar (KDMX), 155 km away, was scanning. The volume nearest the first event began at 16:51 UTC.
1 thunderstorm wind. Local standard time, as filed.
Several reports of 50 to 60 mph winds and tree damage, some of which came from the mPING application. Time estimated from radar.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2018Every state in 2018This day in weather historyWarnings in Iowa, July 2018
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: 773476.