ATLANTA — Snow, ice and a record-breaking blast of cold closed runways, highways, schools and government offices across the South and sent cars sliding off roads Wednesday in a corner of the country ill-equipped to deal with wintry weather. At least 10 people died, including a baby in a car that plunged off a slippery overpass into a Louisiana canal. Icicles hung from a statue of jazz musicians in normally balmy New Orleans, and drivers unaccustomed to ice spun their wheels across Atlanta, which was brought to a near-standstill by little more than an inch of snow.