Another answer is maybe, since the U-2 and the SR
-71 are airplanes.
I have seen thunderstorms topping seventy thousand feet. There is a rule of thumb to clear thunderstorms by a thousand feet for each knot of windspeed. Personally I like more clearance than that.
I have flown over the top of some little cells that were maybe only twelve to fifteen thousand feet, putting me twenty thousand feet above them. Pretty much a non-event. But crowding closer to them is dangerous. As was stated above, they have violent updrafts, in fact that is what is building them. They can also spit a column of intense rain or hail outside the visible storm.
There was a pretty thorough discussion of this just about two months ago here. I don't remember the thread title but there was some good stuff there.
Happiness is not seeing another trite Ste. Maarten photo all week long.