EFU Tornado — Grundy, Iowa

2025-08-18 · near Fern, Grundy, Iowa

Event narrative

Satellite imagery revealed a track in agricultural fields. No DIs were impacted, resulting in an EF-U rating.

Wider weather episode

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.

View location on OpenStreetMap → (42.4895, -92.8552)

Source: NOAA Storm Events Database, event_id 1297861. Narrative written by the NWS forecast office that issued the report.