Cumulus mediocris cloud

Cumulus mediocris cloud
Cumulus mediocris clouds above Auckland with streaks of light precipitation visible in the distance.
Abbreviation	Cu
Symbol
Genus	Cumulus (heaped)
Species	mediocris (moderate)
Altitude	500-3000 m (1,500-10,000 ft)
Appearance	Medium to large cumulus clouds
Precipitation cloud?	Uncommon, but it can develop into a cumulus congestus which is a common precipitation cloud

Cumulus mediocris is a low to middle level cloud with some vertical extent (Family D1) of the genus cumulus, larger in vertical development than cumulus humilis.^[1] It also may exhibit small protuberances from the top.^[2] It may or may not show the cauliflower form characteristic of cumulus clouds. These clouds do not generally produce precipitation of more than very light intensity, but may further advance into clouds such as cumulus congestus and Cumulonimbus, which do.

Classification

Species Cumulus mediocris (Cu med) achieves moderate vertical development, has medium-grey shading underneath.^[1] This larger species is also classified as a low cloud by some authorities and is coded C_L2 on the synop report.

• Varieties: Cumulus mediocris is always opaque and therefore has no opacity-based varieties. A single pattern-based variety, radiatus, is sometime seen when the individual clouds are arranged into parallel rows.
• Precipitation-based supplementary features: Cumulus mediocris can produce virga and praecipitatio features.
• Accessory clouds: The pannus supplementary feature is sometimes seen with precipitating Cu mediocris, however the C_L7 reporting code normally used with this feature is overridden by the C_L2 code that identifies cumulus with significant vertical development. Pileus (cap cloud), velum (apron), arcus (roll or shelf cloud) and tuba (vertical column) features are also occasionally seen with cumulus mediocris.
• Genitus mother clouds: Cumulus mediocris may form as a result of a partial transformation of altocumulus or stratocumulus.
• Mutatus mother clouds: This genus and species type may also be the result of a complete transformation of stratocumulus or stratus.

Cumulus mediocris clouds.

Forecasting

These clouds are common in the advance of a cold front or in unstable atmospheric conditions such as an area of low pressure. They can grow into larger clouds (Cumulus Congestus) which could bring rain, winds and in worse cases, thunder and lightning. If these clouds are present in the morning or early afternoon they show a significant instability in the atmosphere likely leading to storms later in the day (if cloud is thickening, if thinning can lead to calm weather).

Formation

These clouds occur when there is more rising air than the Cumulus Humilis. Like any cumulus cloud this cloud requires convention before developing. This occurs when pockets of air around them become warmer and begin to rise. As the air rises it condenses forming a cumulus humilis cloud as it continues to rise, a cumulus mediocris.^[3]

See also

• Atmospheric convection
• cumulus congestus

References

{Climate}