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
Cloud newly formed cloud is determined mainly by air mass characteristics such as stability and moisture content. If these characteristics change over time, the genus tends to change accordingly. When this happens, the original genus is called a "mother cloud". If the mother cloud retains much of its original form after the appearance of the new genus, it is termed a "genitus" cloud. One example of this is "stratocumulus cumulogenitus", a stratocumulus cloud formed by the partial spreading of a cumulus type when there is a loss of convective lift. If the mother cloud undergoes a complete change in genus, it