Date: April 11-12, 1965
Fujita scale intensity: F4-F5
Dead: More than 260
Damage: More than 200 million dollars
On Palm Sunday, 1965, churchgoers in the Great Lakes were complaining about the unusual heat, but there were no storms forecast for the region.
The lack of warning contributed to more than 260 deaths and 3,400 injuries when the second largest tornado outbreak in U.S. history struck.
Severe thunderstorms across the upper Midwest sparked 51 tornadoes in 12 hours, pummeling Indiana, Ohio, and Michigan especially hard.
Caught off guard, the National Severe Storms Forecast Center in Kansas City, Missouri, raced to send out tornado warnings, but many people never heard them. There were no outdoor tornado sirens at the time, and many TV and radio stations did not regularly air weather alerts.
In addition, many towns were cut off from communications because the severe storms had knocked out all power and telephone lines.
Those residents who did hear the warnings were confused by themwhat was the difference between a tornado forecast and a tornado alert?
In response to the deadly confusion on Palm Sunday, the national warning system was refined to tornado "watches" and "warnings." A watch means conditions are favorable for tornadoes, and a warning means a twister has been sighted or indicated by radar.