- Sometimes forest fires can create their own climate.
- Pyrocumulonimbus are an explosive thunderstorm cloud actually created by the smoke and heat of a forest fire.
- Some of this summer’s fierce fires in the West have sparked vortices of fire.
2021 has been a brutally hot and dry summer in the western United States, with hundreds of heat records broken amid an unprecedented drought that has created a powder keg for the fierce wildfires.
Weather conditions often contribute to the growth and spread of forest fires, with high heat, low humidity, gusty winds and lack of precipitation among the main culprits. But fires can also influence the weather.
Sometimes wildfires can create a spooky witch-brew, including pyrocumulus clouds, thunderstorms, dry lightning, and even fiery tornadoes.
Here is an overview of some types of weather conditions that forest fires can create:
What are pyrocumulus (“fire”) clouds?
Pyrocumulus clouds – aka clouds of fire – look like giant, dirty-colored thunder heads that sit atop a huge column of smoke from a forest fire. Often the top of the smoke column flattens out into the shape of an anvil.
Here’s how it works: When the air above the fire becomes overheated, it rises in a large column. As the air with more humidity rises, it rushes up the column of smoke into the atmosphere, and the moisture condenses into droplets. This is what creates the “clouds of fire” which closely resemble thunderstorms seen before a large thunderstorm.
Sometimes these clouds can get even fiercer, becoming what are called “pyrocumulonimbus” clouds.
A cumulonimbus cloud without the “pyre” part is quite imposing – a massive anvil-shaped power tower reaching five miles high, throwing lightning, wind and rain.
Add smoke and fire to the mix and you have pyrocumulonimbus, an explosive storm cloud actually created by the smoke and heat of a forest fire.
NASA has called these clouds the “fire-breathing cloud dragon”, in part because they can ravage tens of thousands of acres.
What is dry lightning?
To put it simply, according to the National Severe Storms Laboratory, dry lightning is lightning that strikes the ground without rain nearby.
How does dry lightning work? Moist air among the clouds feeds thunderstorms, while the dry air below causes the rain to evaporate before reaching the ground. However, lightning always reaches the surface, where the vegetation is dry due to months of persistent heat and low humidity, which is the perfect ignition to start a forest fire.
What are Fire Tornadoes and Fire Vortices?
Fire whirlwinds, fiery tornadoes and “firenados” – terms for the same phenomenon – are some of the most dangerous elements that firefighters face when fighting forest fires.
Some of this summer’s fierce fires in the West have sparked vortices of fire.
A fire vortex is a “rotating vortex column of ascending hot air and gas rising from a fire and carrying smoke, debris and flames into the air,” according to the Glossary of Terminology of forest fires from the Bureau of Land Management. “Fire vortices vary in size from less than 1 foot to over 500 feet in diameter. Large fire vortices have the intensity of a small tornado.”
These fire whirlpools can form in any size of fire, but they are more destructive in large fires. Created by cold air rushing to replace hot air, the rotating vortex can throw embers and sparks great distances. Eddies usually intensify a forest fire.
Contribution: The Associated Press