When a flash of light crackles across the sky on a hot day, many people call it heat lightning. Thought to occur due to high temperatures and humidity rather than a storm, heat lightning may be one of the most misunderstood weather phenomena. Despite this evocative term’s popularity, there is actually no such thing as heat lightning.
What is heat lightning?
As Weather.com explains, “Many people believe heat lightning is produced by hot and humid conditions, lighting up the night sky without any rain or thunder in the immediate area. This theory is completely false, and heat lightning does not actually exist.”
While lightning caused solely by heat and humidity doesn’t exist, the lightning many people see on hot days is real. When clouds gather in the distance, people can sometimes spot lightning before a storm is close enough for them to hear thunder. Some storms are visible from about 100 miles away, but most people can only hear thunder when a storm is within 10-15 miles of their location. This disconnect may be the origin of theories about heat lightning.
According to Farmers’ Almanac, “when the sky is hazy, as is quite typical on warm, summer nights, the light from intense thunderstorms as far away as 100 miles can be reflected off a layer of haze and up into the night sky. And that’s why you tend to see heat lightning as just a diffuse flash or flicker.”
Heat lightning may also be associated with dry thunderstorms. However, Treehugger is quick to clarify this misconception. “Heat lightning, or “dry lightning” as it is sometimes called, shouldn’t be confused with dry thunderstorms, as these two are different phenomena,” writes Tiffany Means via Treehugger. “In reality, dry lightning is associated with a rainstorm, the rain is just too distant to be visible. Dry thunderstorms produce thunder, lightning, and precipitation, but are called “dry” because their rainfall evaporates before reaching the ground.”