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.

What weather causes altocumulus clouds?

When water from the sea or ground goes to the sky, it does it in the form of water droplets. These droplets are often taken to the sky by the wind. When those water droplets get to a higher altitude, the cool air current makes them condense into the air. When that happens, altocumulus clouds are formed.

What does it mean when you see altocumulus clouds?

Altocumulus clouds that appear on a clear humid morning can indicate the development of thunderstorms later in the day. That's because altocumulus clouds often precede cold fronts of low-pressure systems. As such, they also sometimes signal the onset of cooler temperatures.