Ask A Met: Are Fires Weather?

This week's question comes from Morning Brief reader Tom, who asks "Are fires weather?"

Meteorologist Jonathan Belles: This is actually probably one of the easier questions that we’ve been asked.

No, fires are not weather.

But, and this is a big but, fires can create weather and they can be created by weather.

Basically, all weather is created by some sort of heat, and, obviously, heat is created by fires. Anything that creates heat causes air above it to rise. That's how we get thunderstorms, that's how we get winter storms and hurricanes and everything else that we deal with.

So, fires can create two different kinds of weather.

The first one being thunderstorms. We have what’s called “pyrocumulonimbus,” which is basically a thunderstorm created by fire. Pyro, meaning fire; cumulo, being a heap of clouds; and nimbus, being rain.

The biggest fires that we get often create their own weather, and that's one of the biggest challenges that firefighters have. The biggest fires can create their own atmospheres that can span hundreds of miles. These clouds sometimes can create rain, but more than that, they can create their own wind, which causes the fire to behave completely differently.

That can kick up embers and send them every which way, and create new fires which create their own little weather system. You can see how that goes sideways in a hurry.

The other part of this – and this is something that is relatively new in science – is that these fires can also create tornadoes. Rising air doesn't go straight up. A lot of times, the center of a fire is hotter than the outside of the fire. You get a little bit of differential heating, the center of the fire will rise faster than the outside of the fire, and you get a little bit of a swirl and you get, as we’ve seen in the last several years, EF3-rated tornadoes from fires.

It's definitely an active discussion, especially in the West, where we've been seeing more of them. They've always been happening, but we know more about them because everybody has a camera now.

Weather can, of course, create fires as well.

We see this the most in the West, where you have a desert-ish environment. When you have dry conditions, hot conditions, and you add dry lightning from a storm, those are three things that add up to weather-created fires.

In places where you get some extreme wind, the Santa Ana’s for example, wind will blow through a canyon, snap trees, and that'll break down a power line. If there were no wind, you would get no fire.

This is the same way we think about floods. Floods are not exactly weather, but an impact created by weather. The same is true of fires.

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