Posted by: pyeager | June 20, 2009

Tornado Reports and Tornadoes

The recent week or so has been extremely active of the weather front, with numerous tornadoes and reports of tornadoes; however, these things–tornadoes and reports of tornadoes–are not the same–despite how it’s often reported on the news.

The number of tornado reports is, not surprisingly, a compilation of the total number of tornado reports received, and since seeing a tornado is a frightening experience, one tornado is often reported by dozens of sources. While each of these individual reports might not be counted as a tornado report by the National Weather Service (if they know that five reports came from the same tornado in the same town, they should count it as one tornado report), it often takes time to sort through the reports to eliminate this redundancy.

In addition, the same tornado might be reported in different locations along its path–it’s one tornado even if it’s been spotted in two counties and five towns during a 30-minute time period. Again, by the time the official number of tornadoes is determined, the National Weather Service will have accounted for this information.

For these reasons, the number of reports of tornadoes is typically higher than the number of actual tornadoes (sometimes dramatically so), and members of the media should be clearly making this distinction. If you hear conflicting reports of the number of tornadoes for a given severe weather outbreak, it might be that one reporter is sloppily reporting the number of tornado reports as the number of tornadoes.

The Storm Prediction Center keeps a daily accounting of storm reports.

By the way, I believe that the term reported tornadoes should not be substituted for reports of tornadoes–but that distinction is for another day.

–Paul Yeager

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