Often times during the summer months, lightning can be see across the distant sky. This distant lightning is often referred to as “heat lightning.” Tonight’s weather wise blog will focus on the real origins of heat lightning and how it can even be dangerous!
It’s a hot and humid summer night and you are sitting outside or sitting at the ball park and you notice lightning in the distance. You hear people around you referring to this as heat lightning. Folk weather mythology suggests heat lightning is caused by hot air expanding until it sparks on sultry summer nights. This is an incorrect hypothesis. Heat lightning was named because it is often seen on hot and humid summer nights, a time of year when thunderstorms are common. These flashes are often early warning sign that storms are approaching, because the lightning you see may be moving your way. Heat lightning is not a unique form of lightning, but normal thunderstorm lightning that flashes too far away for its thunder to be heard. So called heat lightning appears as sheet lightning which is actually a standard lightning bolt but the light is reflected off of thunderstorm clouds.
The typical summer weather pattern often promotes lightning to be seen for long distances away from the parent thunderstorm. During the summer, our atmosphere cools after sunset and often times warmer air settles over cooler air near the surface. This is called an inversion. Inversions have interesting properties as they can help bend radar waves and light waves. The curvature of the Earth often allows us to see the lightning but not hear the thunder as sound is more likely to be bounced off the Earth’s surface. With this in mind, lightning (what you know as heat lightning) from summer storms can be seen over 100 miles away from the actual thunderstorm itself!
It is also important to remember that cloud to ground lightning strikes can travel 50-100 miles away from the parent thunderstorm. The mythical heat lightning can often be an indicator that a dangerous storm is close by. A prime example of cloud to ground lightning strikes occurring well away from the parent thunderstorm occurred last night (July 23rd, 2011) in Eastern Indiana.
The radar image above shows a thunderstorm occurring over portions of Blackford and Jay Counties with some lightning strikes being detected close to and within the parent thunderstorm. More intriguing however were the cloud to ground lightning strikes indicated across Southeastern Madison County, over 40 miles away from the parent thunderstorm! For that reason, anytime you hear thunder or see lightning, seek shelter indoors. Most lightning fatalities occur when people are caught outside working or taking part in some recreational activity.
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