From Good Question
GALLERIES: COLORADO'S WORST WILDFIRES
DENVER (CBS4) – The latest indications are that Colorado’s two biggest current fires, the Waldo Canyon Fire and the High Park Fire, won’t be out until the second half of July. That’s without rain — big rain. Fort Collins got some Monday, but it hardly made a dent. CBS4 wondered, is there some way to make weather?
Atmospheric scientist Ed Holroyd has made rain near a wildfire before. He has decades of experience with cloud seeding. Nearly 40 years ago he was part of a team that seeded a cloud near a fire in Australia and made rain.
Colorado is no stranger to cloud seeding.
“There is cloud seeding that is happening in Colorado. It is done fairly quietly,” said Dr. Holroyd.
The fact is, it’s almost exclusively done in winter. Colorado has cloud seeding programs that are cooperative agreements. About 20 percent of the cost is paid by the state, about 20 percent by downstream water users (like other states) and about 60 percent of the cost is paid by ski area operators like Vail Associates or Intrawest, which operates Winter Park and Steamboat Springs.
“So the problem with the clouds is they have drops in them that have no chance to reach the ground,” said Meteorologist Bill Woodley.
Woodley was asked if cloud seeding might work.
“If you have clouds, the answer is yes.”
Then came the buts — but we don’t have the right clouds. Certainly not on the blue sky day when CBS4 talked to him.
“More often than not you don’t have the ideal clouds,” Woodley said.
The day CBS4 talked to Holroyd, there were clouds. It looked like there were plenty of them. But still, the clouds weren’t right.
“Too thin,” said Holroyd. “Their tops are too warm for our style of cloud seeding. The tops must be colder than freezing.”
There are several techniques for cloud seeding.
“We burn silver iodide into an invisible smoke and so it creates snow crystals just like what we saw here.”
Silver iodide has a crystal structure almost identical to ice, so it fools the water into freezing. Holroyd gave a demonstration in a chest freezer, showing how he could begin to make snow. That’s if the clouds are tall and cold enough. Experts say cloud seeding on a good year can increase precipitation by as much as 15 percent.
In the warm months, “We introduce something equivalent to salt, which gathers up moisture and starts gathering up droplets,” said Holroyd.
But it’s made harder by fire.
“Even when you do have a cloud to seed, the cloud contains all this ash; very, very tiny particles, so it’s hard to put enough material into the cloud to get them turned around to get them large enough to form drops to get them on the ground,” said Woodley.
It’s wind that makes wildfires the most destructive. Add a strong wind and any clouds that are present have their tops pushed over because the higher you go, the stronger the winds.
It takes cloud seeding maybe 30 minutes or so to work. Rain might fall downwind, which might be useful because it would wet the ground ahead of a fire. But if you were to induce rain you also might induce lightning and that could be disastrous.
There’s a reason there’s so little cloud seeding in the summer in Colorado. On dry years there simply aren’t as many clouds that might produce rain by seeding. In wet years the chances are better, but why bother then? Still, the state is changing its rules on July 1 to make the permitting easier so any attempt at seeding to fight fires would not get tangled in red tape and it could be considered.
But would it be effective?
“Rarely,” — very rarely said Holroyd.
Woodley agreed — “No you just don’t have the clouds typically in a fire situation and there’s nothing to work with.”
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