If you’ve ever scuffed your socks on carpeting on a dry day and touched metal, or “shocked” someone unexpectedly, you’ve experienced a discharge of static electricity.

Similarly, the most prominent theory of lightning generation is based on collisions between ice crystals and small hail (or graupel) in the mid-levels of a developing thunderstorm.

Small hail, ice crystals aloft – Please note 15 degrees F = -9 degrees C

Lighter ice crystals gain positive charge and are carried by the updraft to the thunderstorm’s anvil, or top. The heavier graupel particles, having acquired a negative charge from the collision, remain suspended by the updraft in the mid-levels of the thunderstorm.

This increasingly negative charge in the lower half of the thunderstorm in turn induces, or forces, positive charge to increase along the ground (and anything attached to the ground).

Charge separation

In the world of electricity, opposites attract. Eventually the negative and positive charges build up to the point the air between them can’t insulate them from each other, leading to the lightning discharge.

Lightning discharge

A couple of caveats here. First, this is how most cloud-to-ground lightning strikes occur. However, roughly 80% of lightning actually occurs within the cloud, never reaching the ground.

Also, this isn’t how all cloud-to-ground lightning takes place. A small fraction of lightning cloud-to-ground flashes occur almost 25kms away from a thunderstorm’s precipitation core, due to positive charge buildup in the storm’s anvil (remember those ice crystals?). These so-called “bolts from the blue” typically contain higher currents than the more ordinary lightning and, therefore, are believed to be responsible for a disproportionate number of forest fires and power line damage.

Bolts from the blue

– From our friends at Weather.com