precipitation. Low-level Low clouds are found from near the surface up to . Genus types in this level either have no prefix or carry one that refers to a characteristic other than altitude. Clouds that form in the low level of the troposphere are generally of larger structure than those that form in the middle and high levels, so they can usually be identified by their forms and genus types using satellite photography alone. Genus stratocumulus (Sc) – This genus type is a stratocumuliform cloud layer of limited convection, usually in the form of irregular patches or more extensive sheets similar to altocumulus but having larger elements with deeper-gray shading. Stratocumulus is often present during wet weather originating from other rain clouds, but can only produce very light precipitation on its own. Species cumulus humilis – These are small detached fair-weather cumuliform clouds that have nearly horizontal bases and flattened tops, and do not produce rain showers. Genus stratus (St) – This is a flat or sometimes ragged nonconvective stratiform type that sometimes resembles elevated fog. Only very weak precipitation can fall from this cloud, usually drizzle or snow grains. When a very low stratus cloud subsides to surface level, it loses its Latin terminology and is given the common name fog if the prevailing surface visibility is less than . If the visibility is 1 km or higher, the visible condensation is termed mist. Multi-level or moderate vertical These clouds have low- to mid-level bases that form anywhere from near the surface to about and tops that can extend into the mid-altitude range and sometimes higher in the case of nimbostratus. Genus nimbostratus (Ns) – This is a diffuse, dark grey, multi-level stratiform layer with great horizontal extent and usually moderate to deep vertical development that looks feebly illuminated from the inside. Nimbostratus normally forms from mid-level altostratus, and develops at least moderate vertical extent when the base subsides into the low level during precipitation that can reach moderate to heavy intensity. It achieves even greater vertical development when it simultaneously grows upward into the high level due to large-scale frontal or cyclonic lift. The nimbo- prefix refers to its ability to produce continuous rain or snow over a wide area, especially ahead of a warm front. This thick cloud layer lacks any towering structure of its own, but may be accompanied by embedded towering cumuliform or cumulonimbiform types.