His name is Colonel William H. Rankin, and he fell through a thunderstorm and lived to tell the tale. After his ordeal Rankin published a memoir that was a bestseller in the early ‘60s, but is out of print today.
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A cumulonimbus cloud is not a thing, it’s a process: an enormous convection cell or heat exchanger between the upper and lower portions of the atmosphere. As it moves, the storms sucks in an enormous river of warm, moist air from the lower atmosphere. This convection current rises to the very top of the storm, cools down, and plummets back to ground level in the form of violent downdrafts. If that sounds a lot like the process leading to the creation of a cumulonimbus cloud, that’s no coincidence at all: the force that births the cloud is also what sustains it. These vertical air movements are what make storms so dangerous for aviation. Glider pilots know well the powerful warm updraft that powers a storm, and call it “cloud suck”, because it can manifest as thermals so strong they seem to pull you into the sky.
From the article:
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