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SAN JOSE (NEXSTAR) – Be thankful if your morning weather forecast has never called for pyrocumulonimbus clouds. What is a pyrocumulonimbus cloud? For those of you who are rusty on your ancient Greek, pyro relates to fire, and pyrocumulonimbus clouds are, in fact, cloud formations produced by wildfires.

Pyrocumulus clouds are similar to the cumulus clouds people are used to seeing. They develop when hot air carries moisture from plants, soil and air upward, where it cools and condenses. The centers of these “pyroclouds” have strong rising air.

It’s pretty common, and it’s a warning sign that firefighters could be facing erratic and dangerous conditions on the ground from the indraft of air toward the center of the blaze. One such rising up from California’s Creek Fire last week may be the largest ever recorded on U.S. soil, according to the San Francisco Chronicle.

Several images of the dark, ominous formation were captured by airline passengers and posted to social media.

The formations can be so damaging that NASA once called them the “fire-breathing dragon of clouds.”

“‘pyroCb’ storms funnel their smoke like a chimney into Earth’s stratosphere, with lingering ill effects,” NASA explained in an overview of the phenomenon.

In some cases, the pyroclouds can reach 30,000 feet and produce lightning. There is evidence that pyrocumulus lightning may have ignited new blazes during the devastating fire storm in Australia in 2009 known as Black Friday.

Similar to the way cumulonimbus clouds produce tornadoes, these pyroclouds can produce fire‐generated vortices of ash, smoke and often flames that can get destructive.

Additional destruction is the last thing California needs right now. More than three million acres have already burned this year. The peak of the state’s traditional fire season is still ahead.

The Associated Press contributed to this report.