A weak shortwave moved across Iowa overnight and through the morning of August 18th. And line of storms with trailing stratiform area passed across the state with the wave through the morning.
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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 weak shortwave moved across Iowa overnight and through the morning of August 18th. And line of storms with trailing stratiform area passed across the state with the wave through the morning. MLCAPE was around 1500-2000 J/kg with a weak 850 mb low level jet sustaining storms. With weak effective shear around 20 kts or less, storms struggled to organize and did not become severe. As storms moved east, there was a pocket of enhanced low level stability with around 100 J/km of 0-3 km CAPE. This was enough to incur low level stretching and result in a few tornadoes in Grundy County. Tornadoes remained in open cropland and did not result in any structural or tree damage, identified by drone and satellite imagery.
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 Aug 18, 5:50 AM CST, 26 minutes earlier. Its key messages:
Area Forecast Discussion National Weather Service Des Moines IA 650 AM CDT Mon Aug 18 2025 ...Updated for the 12z Aviation Discussion... .KEY MESSAGES... - Scattered to widespread showers and thunderstorms over northern and western Iowa continue eastward through the morning. Some stronger storms may produce gusty winds and locally heavy rainfall. - Additional storm development possible through mid-day and into the afternoon. A few strong to severe storms could brief damaging winds and hail up to an inch. - Hot and humid temperatures continue today, especially central and south. - Showers and thunderstorms linger in far southern Iowa overnight into Tuesday morning, with conditions then drying out for most on Tuesday. && .UPDATE... Issued at 230 AM CDT Mon Aug 18 2025 Not a ton of changes in thinking for today's weather, as conditions through the next 48 hrs will be heavily influenced by how storms play out this morning and through the day. Expecting current activity to our west to eventually drift into the area early Monday morning and continue eastward through the area into mid-day. This all generally remains sub-severe early in the morning, but chances for stronger winds do increase as mixing occurs ahead of the convection in the morning. Despite the precipitation forecast persisting through most of the day, there will likely be a lull at some point between the departing morning convection and additional afternoon convection. This afternoon convection will occur as the atmosphere recovers and destabilizes, likely tied to mesoscale features, such as remnant outflow boundaries and/or an MCV. This makes pinning down timing and location difficult for this afternoon, as is evident from the broad marginal risk for severe weather from SPC that encompasses the entirety of Iowa today. For storms today, 0- 6 km shear values will be generally pretty weak, around 20 to 25 kts, limiting the potential for long-lived, organized thunderstorms. Fairly weak 0-3 km shear will also negate the potential for long- lived storms, as cold pools struggle to stay in balance and storms quickly become outflow dominant. That all said, instability will still be quite high today, with 2500 to 3000+ J/kg of mixed layer CAPE, which will certainly be conducive for strong updrafts. Therefore, while these storms may struggle to stay organized, initially strong updrafts could produce damaging downburst winds and hail around an inch as their cores collapse. DCAPE values and low level lapse rates rebound nicely behind the morning convection, especially over southern Iowa, further emphasizing the potential for strong downburst winds. As we get into the evening and overnight hours, the potential for convection will continue to push south and east as surface high pressure increases behind the shortwave. However, there is some hint that the weak boundary/trough trailing the wave will reinvigorate overnight tonight into Tuesday morning, bringing the potential for more scattered sub-severe showers and storms in southern Iowa overnight. A few convection allowing models even bring an MCS into southwestern Iowa by Tuesday morning. However, the placement of the trough will be critical in determining where convection occurs into Tuesday morning, as anything behind the wave will be battling subsiding, stable air. Therefore, while there are storm chances in southern and southeastern Iowa lingering into Tuesday morning, it's possible everything pushes southward and stays almost completely out of the forecast area. High pressure then fills in more by Tuesday and should keep most of the forecast area dry, barring some areas along far southern Iowa, again depending on how far south the boundary sags. Finally, in addition to the convection, temperatures will again be quite warm today, especially in areas that avoid storms in the morning. Cloud debris and cooling temperatures aloft should help keep highs a bit lower again today, but any areas that receive sunshine will again heat up and feel quite muggy. This is especially true in southern Iowa, assuming most of the activity stays north through mid-day. Fortunately, even in these areas, heat indices should stay below advisory criteria, albeit still around 100 degrees F. More relief from the heat then comes on Tuesday as the high pressure brings northerly flow and cooler temperatures aloft, with highs around a more seasonal mid to upper 80s. && .DISCUSSION... Issued at 232 PM CDT Sun Aug 17 2025 Convection early this morning largely remain north of the area aside from a few isolated thunderstorms that crept into northern Iowa. These have dissipated this afternoon, but with the warm front a little further south the temperatures across northern Iowa have remained in the low 80s. Into central and southern Iowa temperatures have again soared into the upper 80s to low 90s with dewpoints in the mid to upper 70s. Similar temperatures are expected on Monday, however there is some uncertainty how much lingering convection (discussed next) will impact highs. Right now it appears there will be a lull in convection from late morning through the afternoon, allowing for plenty of warming. Should showers hang around longer, temperatures will likely be several degrees cooler than currently forecast. Next up are convective trends. Right now the warm front is draped across north central Iowa roughly near the highway 20 corridor. As this lifts north there's a chance for isolated convection to develop on the boundary, aided by more than sufficient instability (3000+ J/kg MLCAPE). Shear remains the limiting factor at under 30 kts and should prevent more robust storm organization this afternoon and evening. Later tonight the wave with ongoing convection across South Dakota slides into northwest Iowa. Initial convection is expected to be the most robust with gusty wind the primary hazard. This line pushes east through the overnight across northern Iowa as a secondary low lifts into the area out of Nebraska and merges with the line. This wave will progress across Iowa through Monday morning, diminishing in strength through the morning as support from the low level jet tapers off. By afternoon diurnal heating is expected to reignite convection along the boundary. Right now this placement looks to be across southeast Iowa, however placement could shift towards central Iowa depending on haw quickly the boundary progresses. Temperatures cool behind the wave with highs in the low 80s middle to end of the week. It's also quiet with the next chance for precipitation not arriving until next weekend. && .AVIATION /12Z TAFS THROUGH 12Z TUESDAY/... Issued at 636 AM CDT Mon Aug 18 2025 Line of storms moving through the area this morning is producing 35 to 45 mph winds, heavy rainfall, and MVFR to IFR ceilings/visibility over central Iowa. These will continue eastward, with stratiform rainfall and occasional lightning behind the line. VFR conditions will develop after this precipitation concludes, but additional isolated to scattered storms will be possible again this afternoon. Confidence is low on exact timing and location of afternoon convection, so have used PROB30s to depict the most likely timeframe. Strong winds, hail, and locally heavy rainfall are possible with these storms. Storm chances diminish from north to south through the evening, with low clouds and even some fog development possible in the north by tomorrow morning. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && UPDATE...Dodson DISCUSSION...Hagenhoff AVIATION...Dodson
Hazardous Weather Outlook National Weather Service Des Moines IA 240 PM CDT Sun Aug 17 2025 IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075- 081>086-092>097-181945- Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo- Pocahontas-Humboldt-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- 240 PM CDT Sun Aug 17 2025 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...This afternoon and tonight Thunderstorm chances this evening into the overnight hours, beginning in northern Iowa then spreading south and east through the night. A few strong storms are possible, with gusty winds being the main concern. .DAYS TWO THROUGH SEVEN...Monday through Saturday Intermittent storm chances continue through Monday, some of which may be strong with gusty winds and hail. Heat continues on Monday with heat indices over 100 degrees possible in southern Iowa. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed tonight into Monday. Hagenhoff
The Des Moines radar (KDMX), 101 km away, was scanning. The volume nearest the first event began at 12:15 UTC.
3 tornado. Local standard time, as filed.
Drone imagery provided by the emergency manager and satellite imagery revealed a track in agricultural fields. No DIs were impacted, resulting in an EF-U rating.
Drone imagery provided by the emergency manager and satellite imagery revealed a track in agricultural fields. No DIs were impacted, resulting in an EF-U rating.
Satellite imagery revealed a track in agricultural fields. No DIs were impacted, resulting in an EF-U rating.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2025Every state in 2025This day in weather historyThe tornado archive for Iowa, 2025Warnings in Iowa, August 2025
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: 1297697, 1297698, 1297861.