Cumulus cloud

Cumulus Cloud
File:Illuminated cumulus clouds.jpg Puffy cumulus illuminated by late afternoon sun far below a NOAA P-3 returning to base at after a mission.
Abbreviation	Cu
Genus	Cumul (heap)
Altitude	Below 2,000 m (Below 6,500 ft)
Classification	Family C (Low-level)
Appearance	Fluffy, white piles
Precipitation	Depends. Cumulus humilis and mediocris, most likely no, but congestus, sometimes yes. Cumulonimbus, yes, but may be virga.

Cumulus clouds are clouds that are usually of a puffy, popcorn-like appearance, with noticeable vertical development and clearly defined edges. They can be found singly, or in lines or clusters. Given enough instability, moisture and temperature gradient, they are precursors of many other types of cloud, for instance, cumulonimbus.

One of the unique characteristics of cumulus clouds is their creation of wind. This happens because the first rain to fall from the base of a cumulus cloud evaporates into the air beneath and cools it, often by several degrees. The cooled air descends. The colder the air is relative to the air around it, the faster it will fall. Thus, a ground observer will generally feel a gust of strong, cold wind being pushed ahead of a large cumulus clouds -- especially in the case of cumulus clouds being generated from the result of a cold front.

The drier the air beneath the cloud, the more capable it is of being cooled by evaporation. Provided there is sufficient rain falling from the cloud, the air will continue to cool. As it drops beneath the cloud, the cold air spreads out in all directions along the ground. The light wind moving in towards the cloud suddenly becomes a squall rushing out from it. Rain falls, often in grey streaks below the cloud, or in a dramatic arch of black cloud spreading out from the parent cloud. These large, precipitating cumulus clouds can extend through multiple levels of the atmosphere and are called cumulonimbus clouds.

Simplified development of a Cu-cloud, given conditions are suitable.

Over the sea, cumulus clouds are normally found in regularly spaced lines. The best examples of these lines are found in the trade winds where they extend for many miles. These create a pattern in the vertical movement of air, causing it to roll horizontally. Between the lines of cloud are stronger, more gusty and slightly veering winds; but beneath the lines of cloud, somewhat lighter and more backing wind.

External links

• Cumulus cloud at BBC Weather
• Cumulus cloud page at University of Richmond internal site