Sometimes very ominous in appearance, Mammatus clouds are harmless and do not mean that a tornado is about to form - a commonly held misconception. In fact, mammatus are usually seen after the worst of a thunderstorm has passed.
Super-cell Lightning, Snyder, Nebraska Under a super-cell thunderstorm, a "wall cloud" or "pedestal cloud" may form. This is frequently associated with tornadoes and micro-bursts. Here, a "cloud-to-ground" lightning bolt strikes from a wall cloud.
cumuluslife: ““… we are the dreamers of dreams, Wandering by lone sea-breakers, And sitting by desolate streams. World-losers and world-forsakers, Upon whom the pale moon gleams; Yet we are the movers.