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
Cumulus humilis cloud Cumulus humilis cloud Cumulus humilis are cumuliform clouds with little vertical extent, common in the summer, that are often referred to as "fair weather cumulus". If they develop into cumulus mediocris or cumulus congestus, thunderstorms could form later in the day. They generally form at lower altitudes (500–3000 m (1,500–10,000 ft)), but in hot countries or over mountainous terrain these clouds can occur at an altitude of up to . They show no significant vertical development, indicating that the temperature in the atmosphere above them either drops off very slowly or not at all with altitude; that is, the adiabatic