Altocumulus Clouds: Warm With a Risk of Storms

Altocumulus are popularly called "mackerel sky"—and for good reason. Besides resembling fish scales, the clouds (which are commonly seen on warm spring and summer mornings) can signal the development of thunderstorms later in the day.

Altocumulus are also commonly found between the warm and cold fronts of a low-pressure system, and sometimes signal the onset of cooler temperatures.

• Precipitation Cloud: No, but signals convection and instability at mid-levels of the troposphere.