Intensifying thunderstorms across the southern and eastern U.S. threatened to unleash dangerous weather conditions.

A spring filled with heavy-hitting weather is ratcheting up once more, as forecasters are warning residents across parts of Texas of "a potentially significant severe threat" Sunday evening. The nasty weather was already moving across North Texas on Sunday morning.

More than 40 million Americans are in the threat zone through Saturday night, stretching from Texas to the Carolinas.