Pyrocumulonimbus.

That’s the term for a cumulonimbus cloud that develops when a large wildfire heats the air up so much that a giant cloud develops. They can develop even if the atmosphere is stable since the forcing is all from the heat of the fire below. If there is wind shear in the atmosphere, they can rotate and sometimes produce a tornado. We’ve seen quite a few of these over the past few weeks as wildfires worsen in the West, but today brought another first. An intense firestorm produced a pyrocumulonimbus cloud with strong rotation in Lassen County, California, and the NWS office in Reno issued a Tornado Warning on it.

This video from Barry Winston on Twitter, shows why this warning was a good call, the intense rotation in this firestorm is clearly visible.

Fire tornadoes happen, but the issuance of a tornado warning on one is a first. My friend and fellow meteorologist Matthew Cappucci at the Washington Post wrote a good explainer about these in 2018 here.

Crazy no? Then again, it is 2020…