Fascinating, Laurence. Thanks for sharing. There are two accepted theories about how rain forms. One, applicable to CB clouds, is that it all starts as ice crystals that grow at first by direct deposit of water molecules onto them. At some point,they are heavy enough to start falling and they grow by accretion, the tiny droplets they hit freeze on them instantly. As they get lower, the temperature of the air increases above freezing and they begin to melt. If they are very big, some survive and hit the ground as hail.
How big can the hail balls be up in the clouds? Maybe 15 cm. The updrafts can be 50 m/s and will keep these big balls up. In fact they can go up and down more than once as they get picked up by different updrafts. Mind boggling what happens up there.