A huge storm system crossing the U.S. threatens to unleash tornadoes Friday in the Mississippi Valley, blizzards in the northern Plains and dry, gusty conditions in Texas and Oklahoma that pose a high risk of wildfires.

A powerful low-pressure system is likely to spawn a dangerous outbreak of severe thunderstorms in portions of the Midwest, South and East, where tornadoes, widespread damaging winds, large hail and flash flooding are all concerns.