Pileus (meteorology)

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A pileus (Latin for cap) is a small, horizontal cloud that can appear above a cumulus or cumulonimbus cloud, giving the parent cloud a characteristic "hoodlike" appearance. Pilei tend to change shape rapidly. They are formed by strong updrafts acting upon moist air at lower altitudes, causing the air to cool to its dewpoint. As such, they are usually indicators of severe weather, and a pileus found atop a cumulus cloud often foreshadows transformation into a cumulonimbus cloud, as it indicates a strong updraft within the cloud.

Clouds that are attached to pileus are often given the suffix "pileus" or "with pileus". For example, a cumulonimbus cloud with a pileus attached to it would be called "cumulonimbus with pileus".

[edit] See also

• Lenticular cloud
• Helm Wind

[edit] References

• Factbytes article on cumulonimbus clouds - An interesting, if sparse, resource on the various types of cumulonimbus clouds.

v • d • e Cloud types High-level Cirrus (Ci) · Cirrus uncinus · Cirrus Kelvin-Helmholtz colombia · Cirrostratus (Cs) · Cirrocumulus (Cc) · Pileus · Contrail Medium-level Altostratus (As) · Altostratus undulatus · Altocumulus (Ac) · Altocumulus undulatus · Altocumulus mackerel sky · Altocumulus castellanus · Altocumulus lenticularis Low-level Fog · Stratus (St) · Nimbostratus (Ns) · Cumulus humilis (Cu) · Cumulus mediocris (Cu) · Stratocumulus (Sc) · Arcus · Fractus · Funnel · Roll · Shelf · Wall Vertical Cumulonimbus (Cb) · Cumulonimbus incus · Cumulonimbus calvus · Cumulonimbus mammatus · Cumulus congestus · Cumulus castellanus · Pyrocumulus · Pyrocumulonimbus · Overshooting top · Accessory Other Noctilucent · Nacreous