December 15, 1998 transcript # 264-2
Subject(s): YellowStone National Park, fires of 1988, lightning, virga
Title: Lightning And Fires

Hi, I'm Dave Thurlow and this is The Weather Notebook. I recently visited Yellowstone National Park on the 10th Anniversary of the Yellowstone fires. The fires burned more than 800,000 acres from June until November 1988. Often times when there's forest fires, humans are at fault or at least blamed, but Phil Perkins, the Fire Management Officer at Yellowstone, explains that most fires in the park are caused by nature.

Phil: "They're mostly lightning-caused. We don't have a lot of human-caused fires."

Dave: "To me, it's one of the funny ironies about fire is that what ultimately puts it out comes from a rain cloud but what ultimately starts it comes from a rain cloud too."

Phil: "What we get here tends to be what we call dry lightning. Again, that's a relative term, it just means that if you've got enough moisture and enough heat to develop a mature thunderstorm, we'll tend to get lightning out of that and so some of the storms will generally produce more lightning so we tend to get a lot of dry storms with very little moisture."

Dave: "And what rain does fall usually evaporates before it hits the ground."

Phil: "That's correct, it falls as virga and just never hits the ground. But it creates that channel for the positive and negative charges to flow and so when we see that---getting some virga---we know that it's establishing a channel for that lightning to travel through."

Virga is rain that doesn't reach the ground, hence a dry thunderstorm -- rain free but not lightning free.

For more information on the Yellowstone fires, be sure to visit the weather notebook section of the Mount Washington Observatory website, which is weathernotebook.org. Our show is underwritten by Subaru, the beauty of all wheel drive, with major support provided by the National Science Foundation.

Chronological history of the fires.