Altocumulus may appear as parallel bands (top photograph) or
rounded masses (bottom photograph).
Typically a portion of an altocumulus cloud is
shaded, a characteristic which makes them distinguishable from the
Altocumulus clouds usually form by convection in an
unstable layer aloft, which may result
from the gradual lifting of air in advance
of a cold front.
The presence of altocumulus clouds on a warm and humid summer morning
is commonly followed by thunderstorms later in the day.