Why Tornadoes Take the Weekends Off in Summer
Weekday pollution supercharges storms in eastern U.S., study suggests.

Tornadoes and hailstorms may take the weekends off during the muggy summer months, according to a new study that reveals new ways human activity can inadvertently sway weather.

Scientists analyzed summertime storm activity in the eastern U.S. from 1995 to 2009 using data collected by the National Oceanic and Atmospheric Administration's Storm Prediction Center.

They discovered that tornadoes and hailstorms occurred at a rate of about 20 percent above average during the middle of the week. In contrast, the phenomena occurred at a rate of roughly 20 percent below average on the weekend.

The findings proved statistically significant—not just a random pattern—and matched up well with similar cycles seen in other kinds of storms, the study authors say.