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Cumulonimbus Pileus |
 | | This causes the water vapor in the slab to condense, and a smooth, elongated, cap-like formation, known as a pileus cloud (pileus is the Latin word for felt cap) appears above the rising mass of the calvus. |
 | | Eventually, the ascending cloud overtakes the pileus, which remains draped over the peak of the calvus until the two clouds merge completely. |
 | | Pileus clouds can help weather-watchers anticipate thunderstorms, as the clouds that generate pileus formations are those most likely to develop into full-blown cumulonimbus clouds. |
| www.theairlinepilots.com /met/cumulonimbuspileus.htm (240 words) |
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