What Is a Dry Thunderstorm?

Beware of Microbursts and Wildfires

Virga Image
Virga is a form of precipitation that never reaches the ground. It is commonly associated with dry thunderstorms. NOAA NSSL

A dry thunderstorm is one that produces little or no rain. While it might seem like a contradiction in terms to have a thunderstorm without precipitation, it's actually quite common in areas of the western United States where the heat index can be very high, particularly in late spring and early summer months with low humidity. 

How a Dry Thunderstorm Occurs

A thunderstorm can be called "dry" when temperature and heat gather below the cloud cover, called the aerial canopy.

It will rain, but the rain and other forms of precipitation never manage to reach the ground. The storm's rain and any moisture evaporate as they fall and near the earth. In meteorology, this event is called virga.  

The #1 Natural Cause of Wildfires

Dry thunderstorms are often the culprits behind massive wildfires when lightning ignites a dry fuel source on the ground during fire weather season, which is the hot summer months. Although there's no rain, at least at ground level, these storms still pack plenty of lightning. When lightning strikes in these arid conditions, it's called dry lightning and wildfires can easily erupt. Vegetation and flora are often parched and readily ignitable.

Even when a light rain does manage to survive and hit earth, this moisture is typically nowhere near enough to have any effect on the fires. These storms can additionally produce severe, strong winds called microbursts that can whip the fires about and shift them, making them hard to battle.

The Potential for Dust Storms

Dry microbursts are another weather phenomenon associated with dry thunderstorms. When precipitation evaporates as it nears ground level, this cools the air, sometimes radically and suddenly. This cooler air is heavier and it tends to plummet quickly to earth, creating strong winds.

And remember—there's little to no associated rain and moisture here. That's already evaporated, causing the microburst in the first place. These winds can kick up dust and other debris in arid regions, resulting in sand and dust storms. These storms are called haboobs in the western states that are prone to them. 

Staying Safe in a Dry Thunderstorm 

Dry thunderstorms can typically be predicted well in advance of the storm so officials can warn residents in vulnerable areas. Incident meteorologists, called IMETs, go on full alert. These specially-trained meteorologists look for the fuels that will help a wildfire spread. IMETs have training in microscale forecasting, fire behavior, and fire operations. They also act as managers who can help coordinate control efforts. Decisions are made on how to best control and contain wildfires based on predictions of wind speed and direction.

Even if you do not receive an alert that the weather in your area is prime for a dry thunderstorm, you'll know because you should hear thunder. If rain doesn't arrive before the thunder, simultaneously, or shortly thereafter, a dry thunderstorm—and the potential for fire—is probably imminent. If there's thunder, there will be lightning, although the severity of the lightning can vary depending on the storm system.

As with any storm, seek shelter if you're outdoors.