It was a warm, fairly humid day across the southeast half to two thirds of Iowa with highs in the mid 80s and dew points in the upper 60s. A surface boundary was situated to the north and west of the state, along with lingering outflows within the state from previous convection.
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.
It was a warm, fairly humid day across the southeast half to two thirds of Iowa with highs in the mid 80s and dew points in the upper 60s. A surface boundary was situated to the north and west of the state, along with lingering outflows within the state from previous convection. SBCAPE values generally peaked in the 2000-3000 J/kg range by the afternoon, devoid of supportive shear though. Storms initiated through parts of central Iowa on northeast along a remnant boundary. The severe nature of the storms were relatively short-lived and relegated to the first few hours of the event. A single severe wind gust was recorded, but a number of sub-severe to large severe hail reports were received, including a report of 2 inch hail near Huxley, IA.
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 May 25, 2:24 PM CST, 2 hours 43 minutes earlier.
Area Forecast Discussion National Weather Service Des Moines IA 324 PM CDT Fri May 25 2018 .DISCUSSION.../Tonight through Friday/ Issued at 319 PM CDT Fri May 25 2018 Severe weather potential and unseasonable hot weather were the main forecast concerns through the weekend. No major changes to the ongoing maximum temperature forecast for Saturday and Sunday as they remain on track for near or record highs for both days. Storms already developing over south-central Minnesota and slowly tracking east-southeast. Tremendous instability present across northern Iowa where SBCAPE and MUCAPE topping out around 4000 J/kg. The effective shear has increased through the day to around 20-25 knots, but with minimal 0-1km bulk shear and helicity (at any level), low tornado threat this afternoon and tonight. Elevated supercells as LCLs range from 1500-2000 feet but do look to persist until the sun sets. Storm motion projects the current storm in Freeborn County Minnesota may clip the far northeast portions of the CWA through around 5 PM or so. Further west, latest IR satellite trends suggest an updraft developing north of Estherville with the cloud tops cooling to near -30C as of 2022z. With the high instability and low shear present, expecting main threat of large hail. However, with the DCAPE around 1000 J/kg and the microburst composite parameter around 2-3 which suggest a slight chance of a microburst (per SPC Mesoanalysis) occurring over the northeast corner of the forecast area. The majority of the hires models are not handling the current convection too well. A few members of the HREF, such as the NSSL and ARW WRF might be doing the best with the trends. Regardless, have pops ending fairly quickly this evening past 03z with a few lingering storms possible across the east prior to 06z. Saturday through Friday...heat looks to persist for several days with the large upper level ridge remaining in control of the weather pattern. Records look possible Saturday through Monday with most standing records in the lower to middle 90s for the 26-28 of May. The GFS and ECMWF suggest a shortwave trough to push into the region by Tuesday into Wednesday and are somewhat in good agreement with timing. GFS is slightly stronger, but still have low confidence with any severe weather potential as the timing looks to be an overnight event. && .AVIATION.../For the 18Z TAFS through 18Z Saturday afternoon/ Issued at 1228 PM CDT Fri May 25 2018 VFR conditions expected throughout the TAF period. There remains a small chance for storms later this afternoon into the evening, but low confidence with timing and location as they appear to be isolated. Left out mention except at ALO where there's a bit more confidence to keep VCTS. && .DMX WATCHES/WARNINGS/ADVISORIES...NONE. && DISCUSSION...Podrazik AVIATION...Podrazik
Hazardous Weather Outlook National Weather Service Des Moines IA 336 PM CDT Fri May 25 2018 IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075- 081>086-092>097-262045- 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- 336 PM CDT Fri May 25 2018 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...This afternoon and tonight Isolated to scattered storms are possible through the evening across central to northern Iowa. A few stronger storms may contain large hail and damaging winds near the Minnesota border. .DAYS TWO THROUGH SEVEN...Saturday through Thursday Unseasonably hot and humid conditions are expected throughout the Memorial Day Weekend into early next week. With this being the first significant heatwave of the season, heat related illnesses are possible. Thunderstorms are forecast late Tuesday into Wednesday. The threat for severe weather is low at this time. No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed. KLP
Special Weather Statement National Weather Service Des Moines IA 435 PM CDT FRI MAY 25 2018 IAZ025-026-252215- Wright IA-Franklin IA- 435 PM CDT FRI MAY 25 2018 ...Strong Thunderstorm Moving through Eastern Wright into Western Franklin County... At 433 PM CDT, Doppler radar was tracking a strong thunderstorm 9 miles east of Elm Lake, or 11 miles east of Clarion, moving east at 10 mph. Half inch hail and wind gusts up to 50 mph will be possible with this storm. Brief heavy downpours are also likely with this storm. Locations impacted include... Dows, Latimer, Coulter, Alexander, Rowan, Galt and Beeds Lake State Park. PRECAUTIONARY/PREPAREDNESS ACTIONS... To report severe weather, contact your nearest law enforcement agency. They will relay your report to the National Weather Service office in Des Moines . && LAT...LON 4271 9365 4283 9358 4283 9324 4260 9330 TIME...MOT...LOC 2133Z 276DEG 9KT 4273 9350 REV
The Des Moines radar (KDMX), 38 km away, was scanning. The volume nearest the first event began at 23:08 UTC.
17 hail, 2 thunderstorm wind. Local standard time, as filed.
Trained spotter reported nickel sized hail along Cameron School Road in NW Ames. Report came via amateur radio.
Amateur radio operator reported quarter sized hail.
Trained spotter reported quarter sized hail.
Public relayed a picture of half dollar to ping pong ball sized hail on the north side of Ames. The image came via a text message picture.
Trained spotter reported nickel sized hail.
Ames Municipal Airport recorded a 61 mph wind gust.
A large tree was split and a power pole was blown down.
Public reported estimated golf ball sized hail along I-35 south of Ames. Report came via text message picture.
Public reported quarter sized hail via the mPING app.
Public reported quarter sized hail via social media. Time estimated from radar.
Trained spotter reported ping pong ball sized hail at the time of the report and ongoing.
Public reported large hail in Huxley via social media.
Large hail nearly tennis ball size was measured and reported in Huxley.
Law enforcement relayed spotter reports of up to golf ball sized hail in Huxley.
Public reported quarter sized hail. Time was estimated from radar.
Trained spotter reported quarter sized hail in Marshalltown, still ongoing at the time of the call.
Trained spotter reported estimated nickel sized hail. Time was estimated from radar.
Trained spotter reported up to nickel sized hail. Report came via text message picture.
Trained spotter reported dime to nickel sized hail.
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, May 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: 753593, 753594, 753595, 753596, 757058, 753597, 757060, 753598, 753599, 753600, 753601, 753602, 757059, 753603, 753604, 753605, 753606, 753607, 753608.