A few days ago we had a crash of thunder here at AccuWeather that made most people jump. As It turned out, that the lightning bolt hit less than a half mile from the building. It was probably even closer to us when it zipped by overhead. That's probably why the boom was so loud. Plus it was a big bolt.

Sensors measured it to be something like 58,000 amperes! So how do thunderstorms form? Thunderstorms come in all different sizes and are triggered in several ways. However, the underlying cause of all thunderstorms is rising, moist air. Air mass thunderstorms are generated when heated surface air rises into somewhat cooler air in the upper atmosphere. This type of storm can produce torrential rain, but rarely do they cause tornadoes. Frontal thunderstorms happen when a warm, humid air mass is forced upward by an approaching cold or warm front. Frontal thunderstorms typically form in a line and, given the right circumstances, can unleash damaging winds, hail and tornadoes.

Friday evening, strong thunderstorms with hail and damaging winds will move from the Ohio Valley toward the central Appalachians. Local wind gusts could exceed 60 miles per hour with these storms, and a few tornadoes cannot be ruled out. Heed all watches and warnings.

Story by AccuWeather.com Senior Meteorologist John Kocet.