Residents of Greensburg, Kansas had about 20 minutes warning before one of these destroyed their town in 2007
Duration of tornado outbreak2, 
56 hours, 9 minutes ... 14 more tornadoes were confirmed on May 6 in the region 
before the... [DOC] [TLE] Students entering 6th grade [PAR] to read at least 20 minutes a day for at least 4 days a week.