My scariest experience would have to be when a tornado was in our area.
We live in Texas, so while they are not common, they are obviously not out of the question.
I was at school, and the intercom went off, telling us all to take shelter in the Gym.
(I got to miss Math class so it wasn't a total loss).
We stayed in the Gym for two hours after seventh period, so basically an hour after school ended.
We were not allowed to leave school premises till the severity of the storm died down.
Thunder was shaking the building, the rain was almost like fog, falling down so hard, you could not see outside.
Lightning continually lit up the dark sky.
We later found out that two tornadoes had been closer to the school than expected, and there were in all, six in our district.
Very scary.
Thankfully, no one was hurt.