Supplementary features and accessory clouds, like
the varieties, aid in the clear identification of clouds.
The most common supplementary features are mamma,
tuba, and virga. They are defined and associated with
the parent clouds in the general section.
Fog is a cloud on Earths surface. It is visible
condensation in the atmosphere. Fog varies in depth
from a few feet to many hundreds of feet. Its density is
variable resulting in visibility from several miles to
near zero. It differs from rain or mist in that its water or
ice particles are more minute and suspended and do not
The forecasting of fog is frequently a difficult task.
In addition to knowledge of the meteorological causes
of fog formation, it is necessary to have a thorough
knowledge of local geography and topography. A slight
Figure 5-1.Layer diagram of clouds at various levels.