3saul, it's not a XPX limitation, it's just how we model the clouds. There is a slider in the SkyMaxx configuration for the cloud sizes, which controls the maximum size the cumulus congestus clouds can reach. This ranges from 500 meters to 5000 meters, so cranking that up should result in larger, thicker clouds. The cloud sizes follow an exponential distribution (as they do in real life,) so it may be rare to get a really big one even with the slider all the way up. You asked specifically about cumulonimbus clouds - these are the "thunderheads" we sprinkle in the scene when X-Plane tells us thunderstorms are present. These are hard-coded to be 5KM across and 7KM tall (we really should add some randomness to that to make them a little more visually interesting - I think I'll do that now). But, these are anvil-shaped clouds and not the sort of towering cumulus cloud in your screenshot. Providing more variety in our cumulonimbus cloud shapes is something we can look at for future revisions. It's actually possible to model your own cumulonimbus cloud shapes if you have 3D Studio Max - any adventurous souls interested in trying it out should PM me for details.