Q: My daughter was reading a novel [where they were] talking about hot lightning and cold lightning. I was wondering if there really is cold lightning?
from Linda Fields

A:  Lightning is always hot.  It is so hot that it rapidly expands the air around the lightning bolt that it creates a supersonic shock wave... which we call and hear as thunder.

But lightning is further classifed as hot or cold based on how long the current, measured in Amps, flows from the strike.

A wonderful resource for lightning information can be found in the book All About Lightning by Martin A. Uman.  In it he wrote:

When lightning flashes, its current reaches its peak of 10,000 to 20,000 amps in a few millionths of a second. The current then decreases in around a thousandth of a second unless it's what's known as a continuing current. A continuing current can be around 100 amps and last for one or two tenths of a second. Strokes with a continuing current are called "hot" lightning because they start fires in wood, Uman explains. As he notes, to start wood burning, the electrical current has to be not only hot, but last long enough. The extra tenth or so of a second is enough to do this. Lightning without the continuing current doesn't last long enough to set wood on fire and is called "cold" lightning.

Remember, cold lightning is just as dangerous to humans as hot lightning.  As we tell the kids, "When thunder roars, go indoors".  And wait 30 minutes from the last sighting of lightning or last sound of thunder before returning to the ball field, the pool or backyard.

If you'd like to see some of Uman's research videos on lightning, you'll want to check these out.

And the Lightning page from the Pueblo, Colorado National Weather Service office has a great number of links to maps, video and other statistics, too.