"The threat for strong tornadoes will rapidly diminish in these areas after sunset, with the main threat becoming damaging straight line winds during the overnight hours, " Morris said.

CNN: Severe weather threatens parts of South

Derechos are thunderstorms with damaging straight-line winds, as opposed to tornadoes, which are thunderstorms with a strong rotational component.

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Straight-line winds of 70 mph were recorded.

CNN: Crews search Smoky Mountain wilderness after deadly storm