"Severe weather outbreak threatens millions across central and southern U.S."

A severe thunderstorm outbreak is bringing the threat of "strong to violent" tornadoes and straight-line wind damage to 42 million people across at least 12 states into Friday night. The Storm Prediction Center (SPC) issued a rare "high risk" storm threat outlook for two areas Friday: parts of Iowa, Illinois and Missouri, and portions of Arkansas, Tennessee and Mississippi. Wind shear is a key ingredient for tornado formation. In addition to the high winds in thunderstorms, high wind warnings are up for several states as damaging gusts are expected due to the intensity of the low pressure area moving into the Upper Midwest.