A few days ago we had a crash of thunder here at AccuWeather that made mostpeople jump. As It turned out, that the lightning bolt hit less than a halfmile from the building. It was probably even closer to us when it zipped byoverhead. 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 aretriggered in several ways. However, the underlying cause of all thunderstormsis rising, moist air. Air mass thunderstorms are generated when heated surfaceair rises into somewhat cooler air in the upper atmosphere. This type of stormcan produce torrential rain, but rarely do they cause tornadoes. Frontalthunderstorms happen when a warm, humid air mass is forced upward by anapproaching cold or warm front. Frontal thunderstorms typically form in a lineand, given the right circumstances, can unleash damaging winds, hail andtornadoes.

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

Story by AccuWeather.com Senior Meteorologist John Kocet.