It's easy to find explanations of the theories of charge accumulation in clouds during storms, as well as ones describing suspected processes leading to lightning channel formation. What I have yet to encounter is any theory describing how a large region of a cloud can be conductive enough (for any duration, long or short) to allow charges to be conducted into a lightning bolt channel.
In other words, how would the ice or water particles that supposedly collect charge move these charges toward a strike channel without some kind of conductive plasma between them? Is there plasma that reaches into large cloud regions? If so, how does it form and what might be the lifetime?