A large scale trough was predicted to move across the northern United States, with associated moisture return from the Gulf of Mexico and ample instability forming a classic plains severe weather setup.

[1] By May 21, models showcased an increasingly strong and robust negatively-titled trough rapidly moving across the United States before slowly stalling through the central plains.

[1][2] At 12:43 pm CDT, the Storm Prediction Center identified through water vapor imagery that a rapidly moving and strong jet streak was approaching from Minnesota to Iowa.

[2][note 1] The southern supercell in a cluster of rapidly intensifying cells began rotating in northeast Iowa, west of Waterloo.

As a tornado-cyclone materialized, a funnel cloud developed, and a tornado touched down two miles south of Aplington near the Butler and Grundy County line at 4:48 pm CDT.

East of Aplington, the tornado traveled through a series of farm fields, leaving distinct cycloidal marks in the corn stubble.

It then tracked into Parkersburg, becoming extremely violent, intensifying to EF5 strength, and growing into a large wedge-shaped tornado as it tore through the southern part of the community just before 5:00 pm CDT.

[4][5][6] Residential areas in Parkersburg were devastated by the tornado, as whole neighborhoods were leveled and entire rows of homes were swept away, leaving only basements behind in some cases.

[2] A rebar support set into the foundation of one home was found snapped in half, hardwood trees throughout southern Parkersburg were completely debarked and denuded, and shrubs were uprooted and stripped in some areas as well.

[3] The tornado maintained EF5 strength as it reached New Hartford, impacting a housing development on the northern side of the town at 5:09 pm CDT.

Multiple well-built homes with anchor bolts were again completely swept away, and vehicles were thrown long distances and mangled beyond recognition, a few of which only had their frames left.

[4] Past New Hartford, the tornado weakened dramatically and passed just north of Waterloo and Cedar Falls, shrinking to about 1⁄4 mile (400 m) in width as it continued to impact rural areas.

Mud and corn stubble was picked up from farm fields near Dunkerton and plastered thickly against fences, power poles, and houses.

[10] After the tornado, Governor Chet Culver declared Butler and Black Hawk counties disaster areas due to the extensive storm damage.