Overshooting top

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An overshooting top protruding above the anvil at the top of a thunderstorm

An overshooting top is a domed structure shooting out of the anvil of a thunderstorm, sometimes into the stratosphere.

Overshooting tops form when an updraft, due to momentum from rapid ascent and strength of lifting, protrudes its equilibrium level. This can occur with any cumulonimbus cloud when instability (usually estimated by convective available potential energy) is high. An overshooting top lasting for more than 10 minutes, however, is a sign of a strong updraft in a thunderstorm and indicates that the storm will likely have severe weather, especially if it is large. If the overshooting top is continuous it means the storm is probably a strong supercell. If the overshooting top is rising and falling downstream then it could indicate that the storm is pulsing and not as strong as a storm with a continuous overshooting top. During a strong tornado the overshooting top might roll over or fold over as new activity climbs up the back while the front of the overshooting top collapses into the storm. During a long-track tornado the whole top of the storm, including the overshooting top, might drop by thousands of feet.