The billboarding scheme for cloud puffs has been rewritten for X-Plane 10; for the most part you should not see puffs spinning or reorienting themselves as you move the camera. However, while poking at the cloud puff shader, I managed to induce this picture on the left. The weather system makes some of the best bug screenshots.
(The post was originally labeled "bug or tornado"...I changed it because it seemed obnoxious after what happened in Joplin, MO - just me being a jerk from the East Coast. A few days later we were hit by a series of Tornadoes fairly close to home.)