The important action happens inside the cloud
The storm contains ice crystals, supercooled droplets and graupel, a form of soft hail. These particles move differently in the updraft and collide. Those interactions help transfer electrical charge.
Air movement separates the charge
Small ice crystals can be carried upwards while heavier particles remain lower down. A common simplified picture has positive charge higher in the cloud and negative charge below it. Real storms can have more complicated charge regions.
The insulating air breaks down
As the electrical difference grows, the air can no longer keep the charged regions apart. A rapid electrical discharge follows. Lightning can occur inside a cloud or between a cloud and the ground.
Cloud shape is only part of the picture
A rain map measures precipitation, not this charge separation. It cannot identify every electrical change inside a growing storm. Learning the science helps explain why a radar image alone cannot determine lightning safety.
Sources & further reading
View the references for this guide
Editorial review: 24 September 2026. Map measurements are updated separately by the provider.