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A sunny day suddenly darkens. Blue skies give way to billowing clouds. Flashes appear and the crackling sound of thunder echoes from the clouds. As you seek a safe place to weather the storm, rain begins to fall and you wonder why you don’t see any actual bolts of lightning hitting the ground.
Don’t be fooled. The crackling sound you hear is actually coming from lightning in the cloud. Although in-cloud lightning goes from one part of the storm cloud to another, it’s usually a warning sign that dangerous cloud-to-ground lightning will soon follow. In fact, in-cloud lightning could also be a warning sign that even worse weather is on the way.
Take, for example, the terrible tornado that destroyed much of Moore, Oklahoma on May 20th, 2013. An hour before the twister touched down, there was no lightning. About 45 minutes before, there was a sudden increase in flashes. Another big increase happened about 30 minutes before this extremely destructive tornado formed.
Could it have been a warning sign? Lightning researchers have noticed that before many violent storms, there is often a sudden increase in in-cloud lightning. They call it a “jump.” It doesn’t always mean a tornado will form, but many severe storms experience a jump in lightning activity before things get really violent.
That makes sense, too. Lightning discharges energy that builds up on particles in the clouds. If there’s a big difference in the charges between two areas of a cloud, a sudden electrical current can form. And what causes these charges? Rapid air movements cause ice particles to collide. Those collisions strip off electrons, creating a charge. The more air movement—the greater the charge.
I know what you’re thinking: we should monitor in-cloud lightning!
Fear not! The GOES-R series of weather satellites should help. From high up in space, they can detect both in-cloud and cloud-to-ground lightning, practically as it happens. These lightning observations will help alert people to dangerous and intensifying storms and may lead to new and better ways to predict and prepare for severe weather!