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Fire's Weather
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Weather can contribute to the start and spread of forest fires--through drought, lightning and wind. Hi, I'm Bryan Yeaton and this is The Weather Notebook.

Sometimes those same fires can actually create their own weather. Correspondent Jeff Rice reports on this phenomenon known as Pyro-cumulous clouds.

Imagine a huge monster of flames that also rises up to spit out thunder and lightning. Forest fires can sometimes become so large and powerful that they can create their own weather systems, and can even create thunderstorms and rain. It sometimes happens in what is commonly called a "blow up." Rick Ochoa, a meteorologist with the National Interagency Fire Center in Boise, Idaho explains.

When the smoke column gets very large, the top of the column can be 20, 30 even 50,000 feet. What we see on top there often times we see large cumulo nimbus type clouds. We call these 'pyro -cumulous clouds.' They're actually a cumulous cloud that is fed by the fire.

This cloud is largely made up of smoke. But there are also other factors at work that can build this plume into a full blown storm.

What happens is when you get these large fires you're getting quite a bit of trees and brush. Obviously, that's moisture being released from the trees. Also a lot of heat. So that in turn you have this big mass of warm ascending moist air-- it sounds like a big thunder storm in the mid west. That's exactly what these smoke columns are. They act very much like thunderstorms. So you start developing these large smoke columns, and then as the moisture starts to condense out you start developing this pyrocumulous cloud this thing will grow and will eventually evolve into the thunderstorm phase… and from there it will start being effected by high winds aloft just like regular thunderstorms are and you'll get lightning and rain, all those types of things you see with a typical thunderstorm.

Lightning from pyrocumulous clouds can actually start other fires downwind from the original source. At the same time, rain from pyrocumulous clouds can sometimes put fires out. The biggest concern for firefighters when these conditions develop is wind. Downdrafts created by the thunderstorm conditions can cause fires to suddenly switch directions, and can even causes powerful tornados of fire.

Correspondent Jeff Rice from Boise, Idaho filed that report. The Weather Notebook is a production of the Mount Washington Observatory and is supported by the Naitonal Science Foundation. Check us out at www.weathernotebook.org.