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Fire Weather
12/30/2002
Listen in RealAudio 
This year more than six million four hundred thousand acres have
burned in one of the worst fire seasons on record -- that's about twice the average. Hi, I'm
Bryan Yeaton for The Weather Notebook
Sometimes a major wildfire actually creates its own weather. Charles Michael Ray tells us
about that.
A firefighter scrapes at the burning forest floor in an effort to cover a hot spot with some
dirt. In the right conditions wildfires like this one can throw burning embers up to a mile,
easily jumping fire lines. Tim Walsh is a fire behavior analyst who is part of an elite Type 1
fire crew. Each season he travels across the nation fighting the worst wildfires. Walsh says
big fires will create a smoke column that can reach 30 thousand feet, sometimes creating
pyrocumulus clouds.
TW: And these pyrocumulus are your white puffy, popcorn-like clouds. They can become so
extreme that they can cause their own rain. The worst phenomena is not when they cause their
own rain, but you get all of this rising and it's a continuous effect of rising air, rising
air, rising air, and all of a sudden this air collapses and it falls very rapidly in
subsidence. And when subsidence happens over a fire it can cause these down drafts with such
power that it spreads fire every direction, very rapidly, spotting well ahead of itself. It's
probably one of the most dangerous occurrences that can happen to a fire.
Walsh says fire crews battling a blaze have to pay very close attention to shifting weather
patterns, even to small changes in wind and humidity, which can drastically effect the fire.
Charles Michael Ray reports in from Rapid City, South Dakota. The Weather Notebook is produced
by the Mount Washington Observatory, and supported by Subaru and the National Science
Foundation.
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