system
Given the following post, respond as if you're commenting on Reddit:
human
[Planetary Sciences] Why is it that sometimes lightnings have no sound? And why does this seem to happen only when there is no rain?

I'm just watching some really cool 'dry lightning' storm out of my place right now. In the midst of the coolness of the show, I started thinking about this! Thanks in advance!
gpt
Thunder is *always* produced by lightning.  When you observe a flash or bolt of lightning, high amplitude (loud) sound waves of many frequencies have begun travelling in all directions (at the speed of sound) from the superheated air turned plasma through which tremendous electric current briefly flowed.

The delay between observing the flash and hearing the thunder is due to the distance from the lightning, and the slow speed of sound in air (relative to light).

During its travel from the bolt to your ears, this sounds energy is subject to *acoustic attenuation*.    When sound propagates through a viscous media, such as water or air, there is always thermal consumption of energy caused by this viscosity.  For inhomogeneous  media (e.g. sheets of rainfall in air), acoustic scattering is another main mechanism for removal of acoustic energy.

The farther you are from the lightning source, the greater the amount acoustic energy is that is lost to thermal consumption and scattering. Ultimately, somewhere, the remaining energy must fall below the threshold of detection.

Thunder is typically absent when observing relatively distant thunderstorms.  This may account for a correlation between lack of thunder and lack of nearby rain.

Edit:  As has been ably pointed out by  subsequent responses, acoustic refraction plays a major role in audibility of thunder at distance.  Be sure to read those replies for this key information.