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Sometimes on a hot, humid day, we see lightning off in the distance. If we're out on a trail or camping in the evening, it's even brighter. It seems to be traveling in almost a sideways motion. We don't see it hit the ground. We don't hear thunder, and it doesn't rain.
I've been told this lightning is just happening because of the temperature and humidity, and possibly a cold front coming through, but there's no storm attached. They call it “heat lightning.” Is that a real thing?
Heat lightning is a myth.
It's normal lighting from a far-away thunderstorm. Lightning is visible 30–50 miles (48–80 km), or up to 100 miles (160 km) over perfectly flat terrain. Thunder is only audible from about 10-15 miles away. So when a storm is more than 15 miles away, but less than 50-100 miles away, you get silent lightning.
The term "heat lightning" comes from the incorrect idea that summer heat somehow causes silent lightning. You're not alone - I picked up this idea when I was a child, and never learned any different until today. I had also heard of "heat thunder," which is supposedly thunder caused by heat, without any lightning or rain. (It's actually just thunder from a storm that hasn't hit yet, but as a child this made a good excuse to stay outside and keep playing until the last possible minute.)
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