As far as I have been able to learn from years of reading, and help me if I am off base here, the updrafts and downdrafts inside thunderstorm cells have been clocked in the 6,000 - 8,000 FPM (feet per minute) range.... just think about the POWER of those numbers... The severe turbulence resulting from these side-by-side columns, some screaming upward, right next to some screaming downward, is the reason that even airliners avoid thunderstorms! It has nothing to do with lightning or rain, the traits most groud persons associate with big storms.
I have had full power (and I do mean FULL) on airplanes from DC-3s to Twin Otters to King Airs and been sucked toward the ground at terrifying speeds [Report to the guys in back: "You ain't gonna like THIS"], and also the converse is true -- I have had the power completely OFF, and been hurtling upward at rates over 3,000 FPM [Report to the guys in back: "WHEEE, UP Elevator!"]. And, this was off to the SIDES of some pretty benign-looking cells. In these cases, we can leave the fire and come back later, or move off to the sides of the cells, wait a while (fuel permitting), and then try again to get the jumpers out safely.
Nothing impresses me more than the power of weather... nothing. So, the other day, when I read about these folks out there, going ANYWHERE NEAR building cumulous clouds with only the barest bones of propulsion, well, it scared the living daylights out of me. "No, thank you." Just call me a true Chicken.
