Dry lightning and heat lightning are often confused. Heat lightning is distant lightning is distant lightning without thunder or rain. It usually occurs when the weather is hot and muggy. Dry lightning is nearby lightning with thunder and with little or no rain. It usually occurs when the weather is hot and dry.
Dry lightning is produced by dry thunderstorms, which are also called low precipitation thunderstorms. These thunderstorms develop just like other thunderstorms, but an absence of low level moisture makes the cloud base unusually high. The air layer under the cloud base is dry. The rain that falls from these thunderstorms evaporates before it hits the ground. This type of rain is called virga. The lightning they produce hits the ground normally.
For fire weather purposes, a dry thunderstorm is any thunderstorm which does not produce enough rain to wet the fuel bed. Rain is measurable when it reaches 0.1 inches, but the ground is just as dry afterwards as it was before the storm.
Some dry thunderstorms can become low precipitation supercells. These usually form along dry lines where a dry air mass meets a moist air mass. A low precipitation supercell can produce normal lightning in a narrow precipitation band and dry lightning everywhere else. They can also produce hail without any other precipitation.
Dry thunderstorms and low precipitation supercells are most common in the Great Plains from Texas to Canada. They can also happen in other places if the air mass is unstable and dry. If this kind of storm connects with a moist air mass, it can change into a classic or high precipitation supercell.
Some dry thunderstorms happen in desert regions. These thunderstorms kick up dust and sand into the air to cause a sandstorm with dry lightning.
Extreme sandstorms can grow into haboobs. Haboobs are common in the south Sahara Desert. They also happen in other very dry regions. The southwestern part of the United States has a haboob about once a year. A haboob in this region is the gust front of a low precipitation supercell and is sometimes followed by rain.
Dry lightning after an extended dry spell is a frequent cause of wildfires. After a few weeks with little rain, the grass, brush, or trees are very dry. A lightning bolt can easily set them on fire. With dry lightning, there is not enough rain to put out the fire.
These fires spread fast because of a dry thunderstorm’s strong winds. The winds are stronger than usual because of higher evaporation. Dry microbursts can spread a wildfire very fast.