METEOROLOGIST JEFF HABY
Two main classifications of clouds are cumulus and stratus. Cumulus clouds result from air rising due
to positive buoyancy (i.e. metaphor: bubbles rising in a pot of water). Stratus clouds results from a forced lifting of
air (low level convergence, upper level divergence). Cumulus clouds are associated with convection. The level in the
troposphere the convection occurs and how deep the convection is will determine the type of cumulus cloud. Shallow
cumulus clouds near the surface are called fair weather cumulus. Shallow cumulus that occur higher aloft are
called altocumulus and even higher aloft are cirrocumulus. If the convection is deep (extending from
low to the upper troposphere) the
result is thunderstorm clouds (cumulonimbus). Stratus clouds are flatter since the rising is not by
convective thermals but rather by an entire layer being gradually uplifted. Stratus on the ground is fog. Stratus
producing precipitation are called nimbostratus. Middle level stratus are called altostratus. Stratus high
aloft are frozen clouds called cirrostratus. A cloud can have characteristics of both cumulus and stratus. This
can occur when shallow convective lifting occurs where forced lifting is also occurring. These clouds
are termed cumulostratus or stratocumulus. On satellite they appear as a sheet of cloud but also with some lumpiness.
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