Strange, I would allow the player to try. That players roll an actual natural 20? I would say, you run, run and run, a small tornadoes is about to form, but you reach the end of your allotted move and the tornadoe falls back to ground after it reach a full inch in height. Not bad, maybe with a haste spell you could have achieve two inches...
I never say no, no matter how ridiculous the attempt is. I once had a barbarian that wanted to jump over a chasm 100 feet wide... I said it would be almost impossible but he insisted. I let him try and guess what? He rolled a f***ing 20. But he fell down the chasm anyways. The player was from another table and he wanted to try mine.
I said, maybe with a jump spell you could have done it. But not by yourself. You knew the rules as much as I. This is on you. He accepted the result but he said that those things were common at his other group. That player is still playing with me 20 years later. But whenever he has a silly idea, which can be often, I just say like your jumping barbarian?