Evacuees watch the wildfire near Fort McMurray on May 4.
How fires create their own weather
00:52 - Source: CNN
CNN  — 

Wildfires such as the one raging in California, can become hot enough to produce rare mushroom-cloud like formations known as pyrocumulus clouds. They tower above the ash and smoke from raging wildfires and are often seen for miles.

A wildfire moves towards the town of Anzac from Fort McMurray, Alberta., on Wednesday May 4, 2016.

Normal cumulus clouds form because the sun’s rays heat the ground, forming warm air that rises because it is less dense than the cooler air above. As it rises, the air cools and condenses to form the cloud.

During a wildfire, however, the extreme heat from the flames forces air to rapidly rise. As the fire burns trees and other plant life it causes the water inside them to evaporate into the rising air. This additional moisture in the atmosphere condenses in the cooler air above, on smoke particles also produced by the fire.

These clouds not only look like thunderstorms, they can act like them too.

Evacuees watch the pyrocumulus form above the wildfire near Fort McMurray on May 4.

“The towering clouds often appear dark gray due to the ash contained in them, and they can even produce lightning and cause the winds to gust and blow in different directions,” said CNN meteorologist Brandon Miller. “This can bring obvious challenges to firefighter battling the blaze.”

Ash and Lightning above an Icelandic Volcano

These are also the same kind of clouds that are seen above erupting volcanoes. They often contribute to the spectacular lightning seen in an ash cloud.