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 storm system that unleashed severe weather for millions of Americans from coast to coast this week is now taking aim at the nation’s midsection, bringing blizzard conditions to the northern Plains, thunderstorms and the threat of tornadoes to the Midwest and South and an elevated risk of wildfires to the southern Plains.

A sprawling storm system crossing the U.S. on Friday overturned semitrucks on highways and fanned wildfires in Texas and Oklahoma, where officials called for ev