Thursday marks the 40th anniversary of the 1974 Tornado Super Outbreak. It is still the worst outbreak in U.S. history.
Other outbreaks have claimed more lives or produced more tornadoes overall, but the outbreak in 1974 had an unprecedented number of large, damaging tornadoes.
The 1974 outbreak produced 23 tornadoes that hit F-4 status, and seven F-5 tornadoes -- the worst on the Fujita scale. The United States typically sees seven tornadoes of that magnitude in an entire year.
Overall, 148 tornadoes took hundreds of lives, injured thousands and destroyed entire communities 40 years ago.
Since then, those communities have rebuilt, and people became more proactive in regard to severe weather. The 1974 event was the catalyst for more tornado research to provide better storm warning systems. The government began investing money into the National Weather Service for better radars and coverage across the country.
All the ingredients came together for a large outbreak that day. A large, low pressure system moved across the middle of the country, pulling warm, humid air, necessary for severe thunderstorm development, into the Ohio and Tennessee valleys. Add the mid- and upper-level support in the atmosphere, and everything was there for a nasty weather day.
Something similar is happening Wednesday and Thursday this week. Another low is developing in the middle of the country that will work its way into the Midwest, bringing a chance for severe weather both days.
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