A dry storm, commonly known as a dry thunderstorm, is a type of thunderstorm that generates lightning but produces little to no rainfall that reaches the Earth's surface.
Understanding Dry Thunderstorms
Dry thunderstorms pose a unique risk, particularly in regions prone to wildfires, because they deliver the ignition source (lightning) without the natural fire-suppressing effect of rain. The definition can vary slightly depending on the context:
- Meteorological Definition: From a general meteorological standpoint, a thunderstorm is considered dry if any precipitation it produces evaporates entirely before reaching the ground. This phenomenon, where rain falls from a cloud but evaporates before touching the surface, is called virga.
- Fire Weather Community Definition: Within the fire weather community, the term "dry thunderstorm" often describes a storm that produces very little rainfall—so minimal that it is ineffective at checking the spread of a fire ignited by lightning. In this context, even a small amount of rain that doesn't significantly moisten fuels is still considered "dry" because it fails to mitigate the fire risk.
How Dry Thunderstorms Form
Dry storms typically form when there is significant moisture at higher atmospheric levels to create clouds and lightning, but very dry air exists closer to the ground. As precipitation falls through this dry layer, it evaporates due to the low humidity, preventing it from reaching the surface. This process can also cool the air, leading to strong downdrafts and gusty winds that can further fan any fires that ignite.
Impacts and Risks
The primary danger associated with dry thunderstorms is their potential to spark wildfires.
- Lightning Ignition: Lightning strikes from dry storms are a leading cause of wildfires, especially in arid and semi-arid environments where vegetation is already dry and susceptible to ignition.
- Fire Spread: The strong, gusty winds often associated with dry downdrafts can rapidly spread these lightning-ignited fires, making them difficult to contain.
- Lack of Mitigation: Without significant rainfall, there is no natural mechanism to dampen the ground or extinguish new ignitions, leading to a higher risk of large, destructive blazes.
For more information on lightning safety and related weather phenomena, visit the National Weather Service.
