Heat Lightning – What It Really Is


Heat Lightning

In meteorology, the term “heat lightning” comes up during warm, summer evenings. This phenomenon, also known as “silent lightning” or “summer lightning,” features distant, silent flashes. Yet, its name and nature are frequently misunderstood.

  • Heat lightning is just normal lightning that isn’t associated with thunder.
  • It is silent either because the thunderstorm is too far away or because atmospheric conditions muffle the sound of thunder.
  • It most often occurs on warm, humid evenings.

What Is Heat Lightning?

Heat lightning is essentially the same as regular lightning, but it occurs far enough away that the thunder sound doesn’t reach the observer.

Common Misconceptions About Heat Lightning

There are several common misconceptions about heat lightning:

  1. It’s a Unique Type of Lightning: A prevalent misconception is that heat lightning is a distinct kind of lightning. In reality, heat lightning is just ordinary lightning from a distant thunderstorm.
  2. Caused by Heat: Many believe that hot and humid weather causes heat lightning. While these conditions aid thunderstorm development, the heat itself doesn’t cause lightning. Instead, lightning results from the electrical discharge within a storm.
  3. No Thunderstorm Present: Another common mistake is thinking that heat lightning occurs without a thunderstorm. Heat lightning is the lightning from a thunderstorm that is simply too far away for the storm clouds or the sound of thunder to be observed.
  4. Occurs Only During Hot Weather: While heat lightning is most common in summer, it occurs whenever conditions allow for distant thunderstorms, regardless of temperature.
  5. It’s Harmless: People often assume heat lightning is harmless because it’s distant and lacks audible thunder. However, it indicates the presence of a thunderstorm that could potentially move closer, bringing risks of lightning strikes and severe weather.

How Heat Lightning Works

Like all lightning, heat lightning results from the buildup and discharge of electrical energy in the atmosphere. This process involves complex interactions between warm and cold air masses. In a typical scenario, the hot, humid air near the Earth’s surface rises and collides with cooler air aloft. This collision creates cumulonimbus clouds, which form thunderstorms.

As these clouds grow, water droplets and ice particles inside them collide, creating an electrical charge. Eventually, this produces lightning – a rapid discharge of electricity. When this occurs far away, with the thunder dissipating before reaching the observer, it’s heat lightning.

Sometimes the properties of air produce lightning without audible thunder, even with a closer storm. This happens when the change in air density with height refracts sound in the troposphere. Or, sometimes thunder reflects off a surface before reaching an observer. Typically heat lightning is as close as 10 miles to a thunderstorm or, with optimal viewing conditions, as far away as 100 miles.

Where Is Heat Lightning Common?

Heat lightning is common in regions experiencing hot, humid summer conditions. It occurs in the Midwest and Southeast of the United States, particularly in the plains and the southeastern coastal regions. It is also common in tropical and subtropical climates worldwide, including the Mediterranean, parts of Central and South America, Southeast Asia, and portions of Africa that experience the monsoon season. The phenomenon is more likely during the evening or night when the sky is clear enough to see distant storms, but the atmosphere is still unstable enough to support thunderstorm activity.

Phenomena Sometimes Mistaken for Heat Lightning

  • Regular Lightning: The key difference between heat lightning and regular lightning is distance. With regular lightning, the thunder is audible, indicating proximity. In contrast, heat lightning’s thunder is too far away to be heard.
  • Sheet Lightning: Another similar phenomenon is sheet lightning, where the lightning flash illuminates an entire cloud base. While heat lightning sometimes appears as sheet lightning due to distance, sheet lightning can also occur nearby.
  • Sprites: While these high-altitude electrical discharge are also silent, sprites are distinctly reddish-orange.
  • Dry Lightning: Dry lightning refers to lightning strikes occurring without significant precipitation at the surface, often causing wildfires. Unlike heat lightning, dry lightning’s thunder can be heard, and it poses a direct threat due to its potential to ignite fires.

Comparing Heat Lightning With Dry Lightning

While heat lightning is simply lightning that occurs without thunder, dry lightning is lightning associated with a thunderstorm that doesn’t produce significant precipitation. Thunder generally accompanies dry lightning. Also, the two types of lightning occur under different conditions and seasons.

Dry lightning most often occurs in parts of the American Midwest and Southwest, Australia, the Mediterranean region, and mountainous regions worldwide. Basically, heat lightning happens in humid, flat, coastal regions, while dry lightning is likely in arid or high-altitude locations. While heat lightning is mainly a summer event, dry lightning is more likely during seasons of prolonged drought in late spring or early autumn.

References

  • Ferguson, Sue A.; Steven, J. McKay; Miriam, L. Rorig; Werth, Paul (2007). “Model-Generated Predictions of Dry Thunderstorm Potential”. Journal of Applied Meteorology and Climatology. 46 (5): 605–614. doi:10.1175/JAM2482.1
  • Füllekrug, Martin; Mareev, Eugene A.; Rycroft, Michael J. (2006). Sprites, Elves and Intense Lightning Discharges. Springer Science & Business Media. ISBN 9781402046285.
  • Graneau, P. (1989). “The cause of thunder”. J. Phys. D: Appl. Phys. 22 (8): 1083–1094. doi:10.1088/0022-3727/22/8/012
  • Saunders, C. P. R. (1993). “A Review of Thunderstorm Electrification Processes”. Journal of Applied Meteorology. 32 (4): 642–55. doi:10.1175/1520-0450(1993)032<0642:AROTEP>2.0.CO;2