The devastating 2011 EF-5 tornado in Joplin, Mo.

Dear Tom,
Despite modern advances in radar technology and the capability of issuing tornado warnings, the Joplin tornado still took a great toll of life. What happened?
— Steve Hanan, Morton Grove
Dear Steve,
The EF-5 tornado that ravaged Joplin, Mo., on May 22, 2011, produced winds in excess of 200 mph and killed about 160 people. The fact that the death toll was high even though warnings were issued 20 minutes before the tornado struck prompted studies to determine warning effectiveness.
Weekend twisters tend to be greater killers because they catch people at home, and the Joplin storm struck on a Sunday. Behavioral studies also showed that despite warnings, many people will not take cover until they can see the tornado, and this storm was partially obscured by heavy rain.