The number of tornadoes in the United States is estimated at over 1,000 per year, causing billions of dollars in damage and killing scores of Americans. The storms occur across the country throughout the year, but are most common during spring and summer months in the Deep South and parts of the Great Plains and Midwest. The National Weather Service and the Storm Prediction Center logs severe weather reports as they occur, including those about tornadoes. Since 1991, nearly 70 people have been killed by them each year, this figure is inflated slightly by 2011's deadliest outbreak.