Met Mailbag is your chance to have a Weather Plus Meteorologist answer your weather question. Each Thursday, our NBC Weather Pulse Blog will publish the answers to questions you send us. This week's question was answered by NBC Weather Plus Meteorologist Elise Finch.

Question: Why does lightning occur?
Submitted by Tanya Platt, Chicago, Ill.

Answer: Tanya, thanks so much for your question.

Lightning is a high-current discharge of electricity. It occurs as the atmosphere tries to balance the positive and negative charges within a thunderstorm and the earth's surface.

When an object with a huge positive or negative charge gets close to an object carrying the opposite charge, a spark jumps across the space between them to neutralize the charges. In a thunderstorm that 'spark' is a lightning bolt.

INTERACTIVE: All About Lightning

The top of a thunderstorm cloud becomes positively charged, while the bottom becomes negatively charged. Static electricity builds up between the earth and the cloud and a spark, that we don't see, comes down out of the cloud. Just before that invisible bolt reaches the ground it's met with a positively charged spark that's moving upward. When these two collide an 'explosion' occurs as the return stroke travels up and the result is the visible flash we know as lightning.

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