Dry lightning causes hundreds of wildfires every year.
Dry lightning is lighting that strikes without any rain. Obviously, “dry” lightning is a bit redundant, as lightning is usually not particularly wet, but the term has become popular because it is so descriptive. The western United States is famous for its dry lightning, which causes hundreds of wildfires each year, some of which grow dangerously.
So-called dry lightning is common in western areas of the US
In a normal thunderstorm, lightning strikes as rain falls from storm clouds, usually accompanied by the sound of thunder. When the lightning strikes the ground, it can cause a spark of flame, but the rain that falls with the lightning extinguishes the fire before it has a chance to spread. In a dry storm, rain is produced but never reaches the ground.
In many western states, storms tend to form extremely high, which means that rain can pass through a zone of hot air on its way to the ground. The dry, hot air causes the rain to evaporate, returning the cloud and fueling the storm, while also ensuring it doesn’t reach the ground to put out lightning fires. These storms are also often accompanied by dry microbursts, blasts of cold air that descend from the clouds and spread rapidly when they reach the ground, causing gusts of wind along the Earth’s surface.
As you can imagine, dry lightning and dry microbursts can be a recipe for disaster. Even when lightning strikes the ground to start a fire, a gust of wind can push the edges of the fire, causing it to spread quickly. In areas where land cover and forests are not well managed, explosive fire conditions can arise during dry lightning storms, quickly covering terrain and sometimes even trapping firefighting personnel.
Generally, the risk of dry lightning can be predicted in advance, with meteorologists using existing data to predict dry storms. In such cases, warnings can be issued to alert people to the risk of fire, and the risk of unpredictable storms leads many communities to encourage citizens to create firebreaks around their homes, keeping the ground cover and grass neatly trimmed. In areas where dry lightning is especially common, building codes may also include built-in fire guards to decrease the likelihood of structure fires.