i remember a storm just like that once when i was a child..

it had gotten over cast, rain was predicted, we were heading home from a local beach, and stuck in traffic..

the road ahead was a hill, and we could see the rain coming like a sheet of water... the car ahead of us was a convertable, and we watched them scramble to get the hood up, (or advance to a near by underpass...) they didn't quite make it, the wall of water advanced fast than they could move! I have never been in storm like that since.