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What that Huge White Cloud Over the Fire is Called
Some have e-mailed LAist asking about the huge white cloud over the fire. "Why is the smoke cloud white during the day?" one reader asked.
It is a pyrocumulous cloud, or fire cloud, "that is created from very intense heat at the surface, usually from wildfires," explained Gary Robbins, resident Sciencedude at the Orange County Register. "The lower part of the cloud is gray, and the upper reaches are white — a normal shading, says the National Weather Service. The clouds are about 15,000-feet high."
The Weather Notebook, a nationally syndicated radio show, describes a lot of what we've been hearing about, such as the fire creating its own wind patterns, and a new concern brought up today--lightning:
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.