Centaurus - most of these 'events' you describe are due to the 'tops' (which do indeed not generally have free water in them) containing rapidly rising air from the clouds below. Hence the importance of looking well down with the scanner during peak activity to see what is 'happening' below.
This is why you can also get a significant 'bump' in clear air near a CB top. There are many and varied significant air currents around a CB.