As the long summer evenings draw to a close, there may be more and more reports of 'heat lightning', the small flashes in the distant clouds without the accompanying thunder. However, heat lightning can generally fall into the same category as centrifugal force, in that it doesn’t truly exist.
The common myth is that the atmospheric heat causes lightning to develop, but in actuality, the storm is just likely very far off in the distance, and the flashes you are seeing are reflections off the clouds.
But lightning always comes with thunder, correct? Thunder is generally caused by the rapid expansion of the heated air. The sound will generally travel for about 10 miles, shorter if it is blocked by mountains or terrain. Additionally, just as light can be refracted by the medium it is traveling through, sound waves can similarly be redirected as they travel between warm and cold air. This can actually cause the thunder to travel much higher in the sky than can actually be heard.
So while there is no such thing as heat lightning, the temperature of a lightning bolt can approach 30,000 K (~53,500 F). So perhaps we can just start calling it ‘Hot Lightning'