Continuous rolling thunder without visible lightning is usually caused by distant lightning strikes or thunderstorms that are too far away for you to see. Here's how it happens:
Lightning strike: When a lightning bolt occurs, it rapidly heats the air along its path to extremely high temperatures—up to 30,000 Kelvin (53,540 degrees Fahrenheit). This sudden heating causes the surrounding air to expand explosively, creating a shock wave known as thunder.
Sound propagation: Thunder travels as a series of sound waves through the air. The sound waves generated by lightning initially travel in all directions, but they become more focused in the direction of least resistance or where there are atmospheric conditions that favor sound propagation.
Atmospheric conditions: The behavior of sound waves can be influenced by various atmospheric conditions, such as temperature, humidity, wind, and air density. For example, temperature and humidity gradients in the atmosphere can act as layers of different refractive indices, causing sound waves to refract or bend.
Reflection and refraction: As sound waves travel through the atmosphere, they can encounter objects like mountains, hills, buildings, or layers of air with different properties. These objects can reflect or refract the sound waves, redirecting them and allowing them to travel greater distances.
Distant lightning and thunderstorms: If there is a thunderstorm happening at a significant distance from your location, you may not be able to see the lightning associated with it due to the curvature of the Earth or obstacles blocking your view. However, the sound waves produced by the lightning can still travel through the atmosphere and reach your location. The continuous rolling thunder you hear is the result of multiple sound waves from different lightning strikes arriving at slightly different times due to their varying distances from you.
It's worth noting that the intensity and duration of the rolling thunder can vary depending on the distance, atmospheric conditions, and the specific characteristics of the thunderstorm.