As Stuart alluded to in his introduction to this topic, often inclement weather will surprise you with its moods and drama, and certainly makes as many shots as it ruins. As such, here are my entries for this show and tell:
Massive thunderheads banking up over an Idaho meadow:
Heavy rain over Lake Rotoiti, Nelson Lakes National Park , NZ. Look closely and you can see the raindrops hitting the lake:
One of the largest and most dramatic cloud formations I've ever seen over Los Angeles: