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.
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A dome-like protrusion above a thunderstorm anvil, representing a very strong
updraftand hence a higher potential for severe weather with that storm. A persistent and/or large overshooting top (
anvil dome) often is present on a
supercell. A short-lived overshooting top, or
one that forms and dissipates in cycles, may indicate the presence of a
pulse storm or a
cyclic storm. See Figs
HP Storm
LP Storm
supercell
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