By 4:00 p.m. CDT (21:00 UTC), light rain began falling over the area, and at 4:30 p.m. CDT (21:30 UTC), a thunderstorm spawned an F3 tornado about south of Rochester, near Pleasant Grove. The tornado killed two people, injured ten others, and damaged at least four farmsteads, one of which it destroyed. After the passage of the storm, conditions briefly improved. At about 6:00 p.m. CDT (23:00 UTC), residents of Rochester noticed a "low bank of cloud"—a thunderstorm—southwest of the city. Few residents were alarmed, but the storm rapidly grew in size and intensity as time passed.