growing top of the cloud. There are also cumulus cataractagenitus. These are formed by waterfalls. Forecast Cumulus humilis clouds usually indicate fair weather. Cumulus mediocris clouds are similar, except that they have some vertical development, which implies that they can grow into cumulus congestus or even cumulonimbus clouds, which can produce heavy rain, lightning, severe winds, hail, and even tornadoes. Cumulus congestus clouds, which appear as towers, will often grow into cumulonimbus storm clouds. They can produce precipitation. Glider pilots often pay close attention to cumulus clouds, as they can be indicators of rising air drafts or thermals underneath that can suck the plane high into the sky—a phenomenon known as cloud suck. Effects on climate Due to reflectivity, clouds cool the earth by around , an effect largely caused by stratocumulus clouds. However, at the same time, they heat the earth by around by reflecting emitted radiation, an effect largely caused by cirrus clouds. This averages out to a net loss of . Cumulus clouds, on the other hand, have a variable effect on heating the earth's surface. The more vertical cumulus congestus species and cumulonimbus genus of clouds grow high into the atmosphere, carrying moisture with them, which can lead to the formation of cirrus clouds. The researchers speculated that this might even produce a positive feedback, where the increasing upper atmospheric moisture further warms the earth, resulting in an increasing number of cumulus congestus clouds carrying more moisture into the upper atmosphere. Relation to other clouds Cumulus clouds are a genus of free-convective low-level cloud along with the related limited-convective cloud stratocumulus. These clouds form from ground level to at all latitudes. Stratus clouds are also low-level. In the middle level are the alto- clouds, which consist of the limited-convective stratocumuliform cloud altocumulus and the stratiform cloud altostratus. Mid-level clouds form from to in polar areas, in temperate areas, and in tropical areas. The high-level cloud, cirrocumulus, is a stratocumuliform cloud of limited convection. The other clouds in this level are cirrus and cirrostratus. High clouds form in high latitudes, in temperate latitudes, and in low, tropical latitudes. Cumulonimbus clouds, like cumulus congestus, extend vertically rather than remaining confined to one level. Cirrocumulus clouds Cirrocumulus clouds form in patches and cannot cast shadows. They commonly appear in regular, rippling patterns or in rows of clouds with clear areas between. Cirrocumulus are, like other members of the cumuliform