There are about 1,000 tornadoes in the United States each year. Compiling an actual average is difficult since reporting methods have changed over the last several decades so the officially recorded tornado climatologies are believed to be incomplete. Some tornadoes, especially ones that cause little or no damage in remote areas, may not be reported. The three-year average for 2007 to 2009 is 1,316 tornadoes per year. The largest single outbreak of tornadoes occurred on April 3 and 4, 1974; 148 tornadoes were recorded in this “Super Outbreak” in the Great Plains and Midwestern states. Six of these tornadoes had winds greater than 260 miles (420 kilometers) per hour and some of them were the strongest ever recorded.