The beach of Moutchic in Lacanau, southwestern France, as clouds of smoke rise into the sky from the Gironde wildfire on July 24, 2026. —Maximilien Lamy––AFP/Getty ImagesFerocious wildfires in France and Spain have prompted the evacuation of hundreds of thousands of people, as firefighters battle against changing winds to get the blazes under control.An added difficulty has developed in France thanks to the emergence of a rare meteorological phenomenon—a pyrocumulonimbus, more commonly known as a "fire cloud." Officials in the badly-impacted Gironde region, near Bordeaux, confirmed the formation of what is understood to be France’s first-ever reported fire cloud over the weekend.As of Wednesday afternoon, firefighters in the south-western Gironde region continued battling the blazes as temperatures reached around 39°C (near 102°F) amid another western Europe heat wave.Satellite imagery of Castellón, a province near Valencia, Spain, also shows what is thought to be a "towering pyrocumulus" fire cloud rising above part of the impacted area.Amid concern the high temperatures may result in the fires worsening or contained blazes restarting, there are also fears that fire clouds, often thought of as fire-generated thunderstorms, could make the wildfires more dangerous.Sophie Brocas, the prefect of Gironde, told reporters the firestorms created by the phenomenon were a sign the crisis had entered a “new dimension.”Here’s what you need to know about the rare phenomenon—and the hazards associated with it.What is a fire cloud?Described by NASA as a "fire-breathing dragon of clouds," fire clouds are created by the intense heat of wildfires, generating an updraft of superheated, fast-rising air that can trigger powerful storms.Jean-Baptiste Filippi, a researcher at the French National Centre for Scientific Research (CNRS), tells TIME that the clouds fall into two categories: pyrocumulus and pyrocumulonimbus (also known as pyroCb).He explains that pyrocumulus is the first stage of a fire cloud. As the wildfire releases large amounts of heat, the air near the ground heats up and rises rapidly, generating a strong upward current."That's level one, because you're adding this to the energy of the fire to create the convective column," he says, referring to a vertical stream of hot, rising gas.As the warm air reaches higher layers of the atmosphere, it cools and expands. When the temperature falls low enough, the water vapor in the air begins to condense, forming a cloud above the smoke column."Level two is pyrocumulonimbus," he says. "Imagine now that this energy is enough to overshoot the lower atmosphere and go up to almost the stratosphere."For this process to occur, there needs to be a combination of intense heat from the wildfire and extreme weather conditions that allow the cloud to develop."The energy is there anyway. It's ready to be released," Filippi says. "It's going to be triggered on top of the fire, and then it will start to interact and make it blow up. If the fire was not there, it would probably be a storm, but somewhere else."It is the combination of weather conditions that would ordinarily produce a dry thunderstorm and an active wildfire that creates this phenomenon."It's because both are occurring at the same time, and it's this combo that is causing the problem," Filippi tells TIME.How do fire clouds make wildfires more dangerous?Fire clouds can make areas already engulfed by wildfire significantly more hazardous—not only for firefighters trying to contain the blaze, but also for people living nearby.The clouds create conditions that can make fires stronger and allow them to spread more rapidly.Filippi explains that the storms created by the pyrocumulonimbus, which loom over the fire, create gusts of wind, which in turn lead the water vapor further into the clouds."Then the fire is raging more and propagating at [a] higher speed with more energy, so it injects even more water vapor. The cloud is getting bigger, and then it is sucking air [in a stronger way]. Then you have this feedback loop, making an acceleration," Filippi says.Those conditions make fires more difficult to contain because the feedback loop continually strengthens both the fire and the cloud above it.Additionally, studies have found wildfire smoke can make some clouds denser, making it harder for them to drop rain that could help dampen the fires.Even when water droplets do fall, if the rain is falling into hot air, "it's gonna evaporate before it reaches the ground," Filippi says.Instead, "you're gonna have a big downdraft. You're gonna have thunder. Then you can have some other effects, like lifting ashes up into the stratosphere," he notes, adding that the ash could later fall onto neighboring areas, raising the need for precautionary evacuation measures."It's also lifting burning material, like spotting fire, so it does propagate some burning pieces of wood that could fall down afterwards," he says.This aerial photograph shows smoke emanating from the wildfire north of the Arcachon basin, with a view of a beach and the Atlantic Ocean near Lege-Cap-Ferret, southwestern France, on July 24, 2026. —Romain Perrocheau––AFP/Getty ImagesFire clouds are expected to become more commonPyrocumulus and pyrocumulonimbus remain relatively rare in Europe. Further afield, fire clouds were observed during Australia's 2019-20 bushfires and in California's 2020 wildfire season.Filippi warns, however, that climate change could make these events more common in Europe."You need stormy conditions, and then you need fire. We are going to have more stormy conditions, and we are going to have more fire. So the probability of having both together, at the same place and at the same time, is higher," he says.Spanish Prime Minister Pedro Sánchez has referred to the current wildfire crisis as "the most painful expression" of the climate emergency."You have more energy in the atmosphere with climate change, you have more water vapor in the atmosphere because the sun is evaporating more water from the oceans," Filippi says. "So more water and vapor means more latent energy. That is just one thing to be released. That's why you have more rain too, and more floods, so the potential of storms is higher."As such, governments have already started preparing for more extreme weather conditions.In France, the government earlier this year launched an initiative to expand mandatory vegetation-clearance rules in an effort to reduce the intensity and spread of fires around buildings.Spain introduced a new national Forest Fire Danger Index at the start of the summer, which combined weather data with satellite observations of vegetation, soil moisture, and land use, allowing authorities to identify areas of extreme danger of forest fires.Signifying the growing concern across western Europe, the U.K. government also strengthened its wildfire resilience heading into the warmer months.