During today's 5 pm newscast, I showed how HD Doppler identified the lightning strike that set a home on fire in the Woodlands. Frequently, when we show lightning strikes on TV, we indicate that there is both negative and positive lightning. But during the summer time, it's the positive lightning that is the most dangerous. Here's a rundown on the two types of lightning:

Negative Lightning

A bolt of lightning usually begins when an invisible negatively-charged stepped leader stroke is sent out from a cloud. As it does so, a positively-charged streamer is sent up from the positively-charged ground. When the leader and the streamer meet, the electrical discharge takes place up the streamer into the cloud. The return stroke is the most luminous part of the strike and the part that is visible.
Most lightning strikes usually last about a quarter of a second. Sometimes, several strikes will travel up and down the same leader strike, causing a flickering effect. Thunder is caused when the discharge rapidly heats the air around the strike, causing a shock wave to be sent out.
This type of lightning is known as negative lightning due to the discharge of negative charge from the cloud and accounts for over 95% of all lightning.

Positive Lightning

This type of lightning represents less than 5% of all lightning. It occurs when the stepped leader forms at the positively-charged cloud tops, with the consequence that a positively-charged streamer issues from the ground. The overall effect is a discharge of positive charges to the ground.
Research carried out after the discovery of positive lightning in the 1970s showed that positive lightning bolts are typically six to ten times more powerful that negative bolts, last around ten times longer and can strike several miles distant from the clouds.
As a result of their power, positive lightning strikes are considered more dangerous. Positive lightning is now thought to be responsible for many forest fires and house fires during summer pulse thunderstorms.

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