Understanding ‘dry’ thunderstorms
August 4, 2022
HASTINGS, Neb. (KSNB) - This past weekend, Scottsbluff, Nebraska experienced a wildfire that scorched thousands of acres of land and damaged nearby homes. This particular fire was thought to be started by what’s called a dry thunderstorm.
“Dry thunderstorms” is a phrase used quite often in the wildland fire fighting community. It is usually meant to describe thunderstorms that produce little or no precipitation at the surface. The “drier” the thunderstorm, along with dry vegetation, the higher the chances of a fire being ignited by cloud to ground lightning. A thunderstorm is considered to be dry when little to no rain reaches the surface. Usually this is the case when you have a high cloud based storm, let’s use 16,000 feet as an example, and very dry air below the cloud base. As rain falls from the cloud it quickly evaporates into the dry air below with very little rain making it to the ground. In meteorological terms, rain that evaporates before making it to the ground is called virga. When lightning strikes from the cloud to the ground, there is not enough moisture to drown out the flame that is started. Add lots of dry fuel and gusty winds, you can end up with a raging fire.
Not all dry storms are completely dry. Some may still produce heavy rain but only over a very small area. Lightning can strike outside of the small footprint of moisture where there is little or no rain falling. The most common region for experiencing dry thunderstorms is the interior west. Whether a thunderstorm is dry or wet, lightning is always a danger and doesn’t have to start a fire to cause damage.
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