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Western wildfires are strengthening storms a thousand miles away : NPR


Western wildfires that burned in 2018, like the River Fire in Lakeport, California, sent plumes of smoke to the central United States, where it helped spread more destructive thunderstorms.

Noah Berger / AP


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Noah Berger / AP


Western wildfires that burned in 2018, like the River Fire in Lakeport, California, sent plumes of smoke to the central United States, where it helped spread more destructive thunderstorms.

Noah Berger / AP

At the end of July 2018, big forest fire burning throughout Northern California. At the same time in Colorado, the weather warning went out of warning heavy thunderstorms and baseball-sized hail.

The two disasters are thousands of miles apart, but scientists are now finding them to be related.

Huge plumes of smoke and heat rising from wildfires in the West are having far-reaching effects across the country, even beyond the hazy skies. That summer, smoke blew into the central United States, where it extended into established summer thunderstorms.

The collision made those storms even more extreme, increasing rainfall and hail by more than 30%, according to one new research in Proceedings of the National Academy of Sciences.

“That might come as a surprise to many people,” said Jiwen Fan, Laboratory Fellow at the Department of Energy’s Pacific Northwest National Laboratory and the study’s author. “I’d really like to see if there’s a connection between them.”

Understanding the effects of wildfires on downstream weather patterns can help improve forecasts in those areas. In the central United States, extreme summer storms can pose a dangerous threat, often causing millions of dollars in damage.

“Scientists are proving that everything is indeed connected,” said Danielle Touma, a postdoctoral researcher at the National Center for Atmospheric Research who was not involved in the study. “And we can’t just think about where we live, we have to think about what’s happening in other parts of the world.”

Smoke helps provide extreme rainfall

While it may seem like raindrops are simply pouring out of the clouds, those drops would not have formed without a seed to initiate them. Raindrops need microscopic particles, called aerosols, which can be dust, soot, or even bacteria, suspended in the air.

Fan said: “Many people don’t realize, before it rains, you have to have tiny particles. “They’re tiny particles that you can’t see with the naked eye.”

Hail from summer thunderstorms in Central America can be seriously dangerous and cause millions of dollars in damage.

Sean Waugh / NOAA / NSSL, VORTEX II


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Sean Waugh / NOAA / NSSL, VORTEX II


Hail from summer thunderstorms in Central America can be seriously dangerous and cause millions of dollars in damage.

Sean Waugh / NOAA / NSSL, VORTEX II

The particles give the water something to condense on, eventually becoming heavy enough to fall to the ground. In 2018, as the Carr Fire and Mendocino Complex burned in California, large amounts of particles drifted eastward through the Rockies, where they collided with massive thunderstorms.

More particles facilitated more raindrops, as well as hail, which occurs when strong storms lift particles high in the cloud and water freezes over them. Running complex computer models, Fan and colleagues found that wildfires in the West increased heavy rainfall during storms by 34 percent and heavy hail by 38 percent.

Heat from wildfires also plays an important role, as it can strengthen winds that blow to the central United States. Those winds drew more moisture along the way, providing more fuel for thunderstorms and reinforcing the intense dynamics inside hurricanes. During the July 2018 storms, winds in Colorado peaked at 100 miles per hour.

Sonia M. Kreidenweis, professor of atmospheric sciences at Colorado State University, USA: “These can cause hail damage or flooding, depending on where the rainfall falls. “If the central US isn’t set to have a hurricane, it might not have the same impact.”

Improved weather forecast for extreme storms

Historically, the West’s fall fire season has not overlapped much with the summer thunderstorm season in the central US states. But with climate change creating drier, hotter conditions for wildfires, that overlap could become more common, as destructive wildfires were occurring earlier in the year.

Understanding this long-range effect of wildfires could help improve weather forecasts, giving communities in the central US more accurate warnings for hail and destructive rain.

“If they know that California or Oregon is having an above-average wildfire season, they might want to watch out for more severe storms to come,” Touma said.

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