Sadly, many did not heed what warnings were given and did not take cover as they should have. Driving around when tornado sirens are blowing is never a good thing...
20 years ago, the sirens went off when there was a tornado spotted.
Now the sirens go off when "conditions are favorable for a tornado".
I live up the road from Joplin in Springfield. The sirens go off all the time now, because in tornado alley, the conditions are always favorable for a tornado when it is storming.
A simple matter of "The Boy Who Cried Wolf". Eventually, there is a wolf, but no one believes it in time.