Thanks for the suggestions! When the weather conditions change, what's really taking all the time is "growing" new cumulus clouds. SilverLining creates each cloud shape using a cellular automata technique, which ensures no two clouds look the same. They already share VBO's, it's this simulation of cloud growth that takes some CPU cycles. The way we usually get around that is to create a single cumulus cloud layer at 100% coverage when loading, and then just enable and disable individual clouds at runtime to achieve the desired coverage. I'm hesitant to do that in SkyMaxx Pro, however, since we would need to have three of these 100% coverage layers around in case we need them, and they would each consume quite a few GPU resources even if sitting there unused. Since a lot of users are already on the verge of running out of GPU memory with high resolution scenery etc., this seems like a risky thing to do. However, it could be something we could expose as an option for users who have graphics cards with large amounts of GPU memory. As for clouds forming in front of the plane - check your visibility setting in the weather dialog. Clouds will fade out at the specified visibility distance, so if this is set too low you will see clouds forming close to the camera even if you have a high draw distance set.