What exactly is a tornado cluster? Tornado clusters are sudden outbursts of twisters that can occur over several days. These outbreaks happen more frequently and with more tornadoes involved in each occurrence. It is considered an outbreak when six or more EF-1 tornadoes begin within 6 hours of each other, despite their proximity.

During a recent NOAA (National Oceanic and Atmospheric Administration) study, researchers discovered that the average number of tornadoes, per cluster, has risen from 10 to 15 in recent years. The project involved studying the number of tornadoes per outbreak in addition to the tornado variability. “These discoveries suggest that the risks from tornado outbreaks are rising far faster than previously recognized,” stated Joel Cohen, a mathematical population biologist and head of the Laboratory of Populations at Rockefeller University in New York and Columbia’s Earth Institute.

A record 79% of tornado fatalities have resulted from these deadly outbreaks. During a particularly destructive week in April of 2011, more than 350 tornadoes weaved a destructive path across south-central United States causing more than 300 fatalities. With the increased possibility of multiple tornadoes, state emergency funds as well as the availability of first responders can be stretched to a breaking point.

Understanding the reason for the rise in outbreaks, is still a gray area. Climate change has been suggested as the possible drive for the increased number of tornadoes since weather patterns are in a constant state of flux. But scientists caution against zeroing in on certain conclusions until more data has been analyzed.