What causes most flash flooding?

I was torn between Thunder and Hail storms, I answered Thunder, but when read the explanation it can be "Icy sheets" as well?? Isn't that Hail storms?? confusing 🤔

I'm drowning in rainbows.

i hit, rainbows by accident :)

Memphis doesn't flood

you can often have thunderstorms without any rain

no flooding were I live