California wildfires can create their own terrifying climate


Then the wind, a key element in the spread of forest fires, went haywire. “Even though the surface winds were quite weak, there was a low-level jet over the mountains,” says Craig Clements, fire meteorological researcher (and fire hunter) at San Jose State University. This turbulence produced strong winds which then mixed with the surface, creating gusts. Firefighters battling the fires – already burning uncontrollably, thanks in part to the effect of the NDE – set fires on them as the flames reacted to the changing winds. “They were reporting erratic fire behavior,” Clements says. “And that is probably due to this low level jet that was happening over the area and that dry air that had moved through the area at night.

These forest fires even create their own weather, additional change in wind regimes. “They get so big that they can create their own types of weather conditions because of all the heat and humidity they get,” says Nick Nauslar, a meteorologist at the National Interagency Coordination Center, which helps mobilize resources for them. forest fires in the United States. “And you get a very turbulent environment. The winds are getting irregular and also stronger than they normally would be, because you just placed this huge fire in a complicated landscape.

Think of a campfire: When the fire heats the air, it rises through the treetops, carrying smoke and embers with it. Now turn it into a fire that consumes an entire landscape, and you have great masses of hot air blowing up into the sky, strong enough to pick up twigs and drop them miles away. This creates an area of ​​low pressure around the fire. As the air rushes to fill the void, fire-induced winds form. “And it can do this in very complex and unpredictable patterns, due to the complex nature of the location of the fire in the landscape,” says Nauslar.

It can get downright apocalyptic when a forest fire spawns a fiery tornado, like the one that spun around last Saturday in the Loyalton Fire north of Lake Tahoe. If layers of wind start to move around a fire in opposite directions, they create shear. “It can cause traffic to where it spins or turns, like a tornado,” Clements explains. These winds at the fire front can be up to five times stronger than ambient winds. “Fire-induced wind is what we really suspect is spreading fire,” adds Clements, “but that dynamic is not well planned.

In the atmosphere above a forest fire, the phenomena can become all the more bizarre. When a forest fire spits smoke, the vigorous updraft carries the particles high into the atmosphere. Here, they act as condensation nuclei, attracting water molecules to form a towering cloud. “If it’s deep enough, it becomes pyrocumulonimbus, because it becomes a thunderstorm,” Clements explains. Earlier this year, several of these storm clouds formed from Australia unprecedented bushfires.

It is concerning that massive forest fires in California could spawn pyrocumulonimbus clouds that produce dry lightning – which has exactly put the state in this mess. If that happens, they will in a sense recycled this lightning energy and use it again, causing more fires in the surrounding area. “That and the winds associated with developing these storms could cause the fire to move in different directions,” Clements says. “So that makes it very dangerous, plus the potential for additional ignition.”

And even more ignition potential is literally on the horizon. This Sunday, new thunderstorms will sway in the region as Tropical Storm Geneviève moves north. The new system follows a similar path to the system that produced the first cycle of thunderstorms. As these tropical systems drift northwest and hit cooler waters, “they start to break up and lose all of their storm characteristics,” says Mayeda, the meteorologist. “And sometimes, if the conditions are right, they come across California in a way that can generate dry lightning.” The national meteorological service issued a fire watch Sunday through Tuesday in the Bay Area and south of Monterey, warning that new wildfires triggered by dry lightning are likely. This could create even more dangers for firefighters in the field.

Surprisingly, smoke from the California wildfires has now wrapped around Genevieve, as you can see in the image above. Thick smoke completely covered most of the western United States and reached Canada. Light smoke even made its way to New York (light blue in the image above). “California has become a huge exporter of smoke,” Mayeda says. As the United States struggles to contain Covid-19, partly respiratory disease: Smoke from wildfires can predispose people to respiratory illness and exacerbate symptoms.

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