The May 2003 Extended Tornado Outbreak

Abstract

During a period of 9 straight days during May 2003, strong tornadoes struck each day somewhere in the midwest or eastern United States. This outbreak caused 39 fatalities and nearly a billion dollars property damage.

Clearly, a sustained outbreak like this is an unusual event. We take a look back at the outbreak, examining the synoptic conditions and the skill of operational weather forecasts and considering what synoptic conditions were responsible. We also compare this outbreak against the climatological record of other outbreaks to assess how unusual such an event was. While no other 9-day period in the 86-year record had strong tornadoes each day and no other period in the last 25 years had such consistently tornado-favorable conditions, we found five other outbreaks in the 86-year record were similar to this outbreak in other metrics. We conclude that events of this magnitude will happen roughly every 10 to 100 years.