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El Niño’s Summer Break, Wildfire Smoke May Have Led To Colorado’s Record September

Colorado had a record warm September. The question is why?

Colorado saw record warm temperatures in September, with very few late afternoon monsoon storms. The cause? It could be wildfires that burned over 1,000 miles away.

“The smoke actually reduced the temperatures. That’s the one culprit I can point at that maybe interfered with the typical El Niño response,” said Klaus Wolter, a climatologist at the University of Colorado-Boulder.

Wolter’s theory is that smoke from multiple wildfires that burned over 300,000 acres in the Pacific Northwest may have made it difficult for thunderstorms to form in the state.

Colorado had a record wet May thanks to the El Niño, soils in the state were saturated going into the summer. With the influence of the El Niño, many climatologists thought the summer monsoon would be strong – until the smoke blew in.

“That was an interesting physics experiment….We basically lost our advantage by September and our fire danger crept up….but not much in the forests. It’s easier to dry out the fine fuels,” Wolter said.

"Smoke is not just gas, it's a bunch of little particles. And if you have too many of them, it becomes very inefficient to make droplets."

He will need to do more analysis of the data to be sure, but it has happened before.

“I’ve seen this a few times in the past, 2000 is probably the best example for a smoky summer in Colorado, even though we had very few fires of our own. And if you look at the physics of how it rains in the summer when you need thunderstorms to develop, having smoky skies is really detrimental.”

Three different components, all caused by the smoke may have contributed to the lack of rain in the state. First, it interferes with convection or the vertical building of thunderstorms because the particulates in the smoke reduce the amount of light that reaches the ground. It also makes it difficult for precipitation to form.

“Smoke is not just gas, it’s a bunch of little particles. And if you have too many of them, it becomes very inefficient to make droplets,” Wolter said. “So you’ve got less heating of the ground, you have these particles in the air that over seed, and then the third factor is that smoke typically hangs about 18,000 feet above ground. And that’s an important layer. To get a thunderstorm you have to break through that. And when you get these inversions that are anchored by that smoke, it makes it that much harder to get a thunderstorm to break through that.”

Smoke and fire consume dry forest during the 2010 Reservoir Road wildfire north of Boulder
Credit Nathan Heffel / KUNC
Smoke from wildfires in California, Oregon, Washington, Idaho and Canada have been blown into Colorado for months, possibly changing the state's weather.

It’s a trifecta, Wolter notes. The disparate components can work against weather in the presence of large-scale wildfires. The drier it got in August and September the easier it was for the soil to heat up and keep Colorado in the 90s.

“It’s important to note that El Niño itself took a bit of a break in the summer,” Wolter said. “It did not grow as furiously in July and August as it had done earlier. It’s now growing again. It’s on track again to becoming a super El Niño.”

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