Five people, including three children, died when an overnight tornado ripped through a mobile home park in the small town of Woodward, in northwest Oklahoma. The storm destroyed about 100 homes and businesses there.
The town's 20 outdoor tornado sirens didn't work because they were knocked out when lightning struck a tower used to activate the warning system.
The same storm system also damaged a small hospital in southwestern Iowa, where a twister shattered windows and ripped the roof. Twenty patients were inside when it hit, but no one was seriously injured.
In the end, only the Woodward tornado proved fatal. While it's unknown whether the disabled sirens contributed to the toll in Woodward, residents and officials in hard-hit areas of Kansas, Iowa and elsewhere credited days of urgent warnings from forecasters for saving lives.
The Associated Press contributed to this report.