Weather in Depth: What is heat lightning?

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Have you heard of, or used, the term “heat lightning?” People usually attribute this term to lightning that believe is formed by heat and humidity — when in reality it is just lightning that can be visible from distant thunderstorms. 

Wednesday night in our region, many folks along the shoreline of Lake Ontario were the audience to a wonderful light show, but they did not hear any thunder. What was happening here is that we had a distant thunderstorm over Lake Ontario that produced hundreds of lightning strikes which were visible but no thunder was heard. This is because from our viewers’ standpoint, they were too distant away to hear any thunder. The sound of thunder from a thunderstorm only travels about 10-15 miles away from its parent storm. That distance can be even shorter when the atmosphere is humid, as the sound waves get refracted by the denser air while lightning can be seen upwards of 150-plus miles away (depending on visibility conditions)! The humid air from Wednesday night shortened distance in which the thunder could have travelled, and left many of our viewers with the light show they witnessed.

The term “heat lightning” is just regular lightning that can be visible from a distant thunderstorm with you just being too far away to hear the thunder, it is not a “type” of lightning.