Good day,
I think I posted several subjects in older threads relating to updraft speeds in thunderstorms. Cloud suck is what glider / parachute pilots call it, and it can be very VERY bad.
In a weak thunderstorm, during development, updrafts can reach 40-50 MPH (about 20 M/S or roughly 3,600 feet per minute). So an ascent rate of 20 M/S is possible indeed. A descent rate of over 30 M/S is even more likely in a downdraft.
Now, comparing this to a great plains supercell is another story. In such storms, updrafts can be as high as 150, or even 175 MPH! Get pulled into something like that under a paraglider / parachute and you'll go from 1,000 feet above the ground to 30,000 feet in a mere 2 minutes - and you will not stop at 30 grand either, you most likely will be propelled into the anvil (40 or 50 thousand feet) and carried downwind by the jet stream and land (most likely frozen and dead) several states over.
Remember the Hallam, NE tornado on May 22, 2004? A check from Hallam bank, which was destroyed, landed in Omaha / Papillion Nebraska, over 80 miles away, about 26 minutes after the tornado hit Hallam, where a woman found it falling out of the blowoff-hazed sky into her yard while sweeping up. This could have easily been a person unlucky enough to parachute near such a storm.
The most obvious dangers are as follows, from most dangerous to least, from being drawn up into ANY thunderstorm updraft.
1). Lack of oxygen. Once above 15,000 feet MSL, a table for time of useful consciousness applies. At 20,000 feet, it's about 4 minutes. 25,000 feet, its 1-2 minutes. At 30,000 feet, it's 30 seconds. At 40,000 feet it's 15 seconds. Above 45,000 feet, it's 5-10 seconds. An updraft can bring you to these heights in only minutes.
2). Freezing / frostbite. At high altitudes, especially above 20,000 feet MSL, temperature is often below zero - year round. Degrees F or C, does not matter, it's cold! You can freeze to death, be soaked with supercooled water and / or ice, and be severely frosbitten. Frostbite, if that's all you get (if you're lucky) is nasty, and forms gangrene, which can lead to amputations. You also can quickly become hypothermic and go into shock. Or, you can get ALL of the above.
3). The bends. Just like a diver coming up too fast from under water, going up from near sea-level to high altitude can do the same thing. A rapid ascent, such as from 1,000 feet to over 24,000 feet in 5 minutes can give you the bends as dissolved nitrogen in your blood comes out of solution and forms bubbles. Joint pain becomes severe, then headache, vomiting, and nerve damage. Not good.
4). Hail / lightning. These are dangerous, obviously, to anything being caught inside a thunderstorm. Hail causes bruises, and can break bones. An in-air lightning strike will have obvious consequences.
5). Distance. You can land, or what-ever is left of you, very very far away. Bad scenarios can be carried out to sea, into a desert, forest, mountains, or any place difficult for a search / rescue.
Notes: Falling unconsious and hypothermia can SOMETIMES extend the time until "brain death" due to slowing the body's metabolism. As for the Asian paraglider, this came too slowly as he was probably frozen / hypothermic while panicking first.
