Experts are suggesting that Wednesday's (April 27th) historic outbreak of tornadoes in the South that left at least 297 people dead in six states may have been among the largest and most powerful ever recorded. The death toll is the largest from an outbreak of tornadoes in the U.S. since April 1974, when 315 people were killed by a storm that swept across 13 Southern and Midwestern states. A typical tornado is on the ground for a couple of miles and is a couple hundred yards wide, with wind speeds of about half those of Wednesday's. Only one percent of tornadoes reach the most powerful readings, but Harold Brooks of the National Severe Storms Laboratory in Oklahoma thinks several of the destructive storms two days ago may have been of this type. He told AP, "There's a pretty good chance some of these were a mile wide, on the ground for tens of miles and had wind speeds over 200 miles per hour."

What caused Wednesday's killer tornadoes? It's hard to really know for sure, but Brooks said the weakening of La Nina in the Pacific likely played a small role. Texas Tech University tornado expert Chris Weiss said there's no consensus on whether climate change had an effect, telling AP, "The problem is trying to relate a climate signal to a specific weather event is always dangerous." There have been an unusually large number of tornadoes this month, although they always begin to surge in April, when warm weather begins setting in and dry western air collides with warm moist air moving up from the Gulf of Mexico