Altostratus cloud size again. During the sampling of one cloud, the scientists noted a halo while flying near the top of the cloud, which indicated that the ice crystals were hexagonal near the top. However, farther down, the ice crystals became more conglomerated. Altostratus tends to form ahead of a warm or occluded front, the altostratus gradually thickening into rain bearing nimbostratus. However it can also occur together with cumulus congestus or cumulonimbus at a cold front. "Velum" This is considered a type of cumulonimbus cloud so it is not listed. Altostratus cloud Altostratus is a middle altitude cloud genus belonging to
Flammagenitus (cloud) Flammagenitus (cloud) A flammagenitus, also known as a pyrocumulus cloud or fire cloud, is a dense cumuliform cloud associated with fire or volcanic eruptions that may produce dry lightning (lightning without rain). A flammagenitus is similar dynamically in some ways to a firestorm, and the two phenomena may occur in conjunction with each other. However, either may occur without the other. A flammagenitus cloud is produced by the intense heating of the air from the surface. The intense heat induces convection, which causes the air mass to rise to a point of stability, usually in the presence of moisture. Phenomena