Lightening will be the most spectacular part of the spring and summer severe weather season! 95% of all “cloud-to-ground” lightning strikes travel from the cloud to the ground, but the initial strike (called the “stepped leader”) is barely visible so people presume that the strike originated from the ground.
Lightning occurs because clouds get electrified as liquid drops collide with hailstones and ice crystals within the cloud (negative charge at the bottom, positive charge at the top). As the cloud moves, the ground under it is positively charged. The positive charges especially like to congregate on protruding objects like mountains, trees, poles and buildings.
When the charge gets too strong/unstable, a current flows between the cloud and the ground. First, the almost invisible “stepped leader” travels downward from the cloud to the ground in 50-meter steps. As this stroke nears the ground, it collides with the build-up of positive charges and produces a powerful flash of lightning (called a “return stroke”) that travels upwards into the cloud.
Thunder is caused when air near the lightning strike is quickly heated to 50,000°F and produces a shockwave. Since it takes sound about 5 seconds to go 1 mile, you can tell how far away a lightning strike occurred if you count the time between the flash and the sound and divide by 5. For example, if you count 15 seconds between the flash and sound, the strike was only 3 miles away.