Study: Tornado Clusters Are on The Rise

Tornadoes are touching down in clusters more often than 50 years ago, a new study reports. On some days, more than 30 twisters strike the United States. Even as storms spawn more tornadoes, there are fewer days on which tornadoes occur, according to the study, published Thursday in the journal Science. Since the 1970s, the number of days with at least one EF-1 tornado has dropped from a mean (or average) of 150 to 100.