Big, bruising thunderstorms will hit parts of the Great Plains and Midwestovernight. Wednesday, the worst storms will shift into Tennessee, Kentucky andWest Virginia. The setup favors damaging straight-line winds and large hail,and tornadoes are also possible.The violent weather is being triggered by very cool air in the upper atmosphereriding over heated air at the Earth's surface. This is a very unstablesituation. Put more simply there is no way to keep the warm surface air fromrising abruptly into the cooler air up above. Just picture a hot air balloonrising, and you'll have a good handle on what is going on here.

In any case, the ascending towers of air cool and condense to form massivethunderstorm clouds. The interaction the thunderstorms have with the jet streamis what ultimately causes damaging surface winds and hail.

This continues to be a dangerous weather situation. Storm warnings will beissued by local weather offices when a particular community is deemed to be inharm's way. Stay alert for possible bulletins on the weather in your area untilthe threat has passed.

Story by Senior Meteorologist John Kocet.