The atmosphere in the southeastern U.S. was primed for disaster in late April 2011. Conditions were almost perfect for a massive outbreak of tornado spawning storm cells. Over a four-day period - April 25 through April 28 - at least 356 tornadoes were spun out of a series of atmospheric disturbances that affected an area from northeastern Texas to New York; 199 of those tornadoes, including the deadliest and most powerful, hit Alabama and surrounding states on April 27, 2011, killing 361 people, leaving another 2,700 injured and causing an estimated $4 billion in damage.