April 11, 1965 was Palm Sunday. That day at least 21 tornadoes were recorded with 17 of those being rated as a F3 or higher. By the end of the day 271 people lost their lives with over 3000 more injured from those tornadoes. It is known as the Palm Sunday outbreak and at the time it was the 2nd worst outbreak known and even today, it ranks as the 4th deadliest outbreak on record.
That horrific day led to significant changes to the warning system. Today, tornado watches are issued when conditions are favorable for tornadoes to develop, but back in 1965, tornado forecasts were issued that research found were misunderstood by many. Plus, the limited radar coverage at the time and poor communication of where the tornadoes were meant the storms came as a surprise in many areas.
The current nearly instant communications between the National Weather Service and the media, better radar coverage and system of severe weather watches were all improvements that came from lessons learned from that fateful day.