Dry eclairs are lightning without accompanied rain. Obviously, “dry” lightning is a bit redundant because normally lightning isn’t particularly humid, but the term has been stuck because it’s very descriptive. The western region of the United States is famous for its dry lightning, which triggers hundreds of wildfires each year, some of which become dangerously large.
In a normal storm, lightning falls as rain falls from storm clouds, usually accompanied by the sound of thunder. When 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 there is rain, but it never reaches the ground.
In many western states, storms tend to form extremely high, meaning rain can pass through an area of warm air on their way to land. The hot, dry air causes the rain to evaporate, sending the cloud back and feeding the storm while making sure it doesn’t touch the ground to put out the fires caused by lightning. These storms are also often accompanied by dry microcracks, gusts of cold air coming down from the clouds and spreading rapidly when they touch the ground, causing gusts of wind to reach the Earth’s surface.
As you can imagine, dry lightning and dry microwaves can be a recipe for disaster. Even when lightning strikes the ground to start a fire, a gust of wind can push back the edges of the fire, causing it to spread quickly. In areas where vegetation cover and forests are not well managed, explosive fire conditions can appear during dry storms, which quickly cover the ground and sometimes even trap extinction personnel.
In general, the risk of dry lightning can be predicted in advance, and meteorologists use existing data to predict dry storms. In these cases, warnings can be issued to alert people to the risk of fire, and the risk of unpredictable storms causes many communities to incur citizens to create firebreaks around their homes while keeping the ground covered and the lawn well mowed. In areas where dry lightning is especially common, building codes may also include integrated fire protection, to reduce the risk of structural fires.