- published: 03 Jul 2012
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An overshooting top (or penetrating top) is a dome-like protrusion that shoots out of the top of the anvil of a thunderstorm. When an overshooting top is present for 10 minutes or longer, it is a strong indication that the thunderstorm may be severe.
When a thunderstorm forms, clouds build vertically into the atmosphere until the storm's updraft (warm rising air) has reached an equilibrium level (EL); the point where the surrounding air is about the same temperature or even warmer. This point of equilibrium is often marked by the tropopause. Rather than continuing to rise into the tropopause, the vertical cloud growth abruptly stops, and instead clouds spread horizontally, forming an "anvil" shape on top of the thunderstorm.
An overshooting top forms when a thunderstorm's updraft, due to momentum from rapid ascent and strength of lifting, protrudes its equilibrium level, forming a dome-like structure on top of the anvil. This can occur with any cumulonimbus cloud when instability is high. Whereas anvils form at the equilibrium level, overshooting tops continue to the maximum parcel level (MPL).