Science in the Triangle

Matt Parker

Matt Parker, a N.C. State University associate professor, sounded almost nostalgic when he talked about the more than 700 tornadoes that were reported roaring across the South, Southeast and Midwest in April, about four times as many tornadoes as hit the U.S. during an average April.

Parker is an atmospheric scientist and has studied how tornadoes develop to help improve weather forecasts.

“This was a historic year,” Parker told science writers and educators during a Sept. 27 talk at Sigma Xi in Research Triangle Park.

A spring storm season like this year’s doesn’t come around often. That’s a good thing, considering the loss of life and the devastating destruction the tornadoes wrought.

April 2011 ranks as the most active tornado month on record, according to the National Oceanic and Atmospheric Association. A storm system that moved across Oklahoma, Arkansas, Mississippi, Alabama, Georgia, North Carolina and Virginia in mid-April killed 43 people, 22 of them in North Carolina. One of the tornadoes it spawned April 16 cut a 180-foot-long track through suburban Wake County, Parker said.

A second storm system at the end of the month was even deadlier. It caused a super outbreak of tornadoes in the South that killed more than 300 people in four days, according to NOAA.

A month later, on May 22, a powerful tornado hit Joplin, Mo., killing 157 people. According to NOAA, the Joplin tornado packed winds of more than 200 miles per hour, it was nearly a mile wide and its track lasted 6 miles.

What about climate change? Could that be a cause for the historic outbreak of tornadoes this year?

“We really don’t know,” Parker said.

A tornado is a mere blip in a 100-year data set that tracks changes in the climate, he said. The increase in the number of reported tornadoes, he added, is likely due to better forecasting and warning systems, a higher population density and the increase in the number of storm chasers.

What was devastating and deadly to the people who lived in the tornados’ way could have provided scientists like Parker with a bevy of otherwise hard-to-come-by data.

In May and June of 2009 and 2010, Parker and his team of students were among about 100 scientists who tracked storms with radar, measured wind speeds, sent up weather balloons and fed the information to a database. The study, called VORTEX2, was one of the largest field studies to determine the origin of tornadoes and a follow-on to a more limited tornado hunt in 1994 and 1995. The teams had about $10 million worth of equipment at hand.

April 2011 was never part of VORTEX2′s data collection phase.

Working with tornadoes is often frustrating, Parker acknowledged. May and June 2009 were two very uneventful months - only two storm systems that generated tornadoes.

“Two thousand ten was much better,” Parker said. “On some days we had the pick of tornadoes.”

About 40 storm systems with the potential to generate a tornado, also known as super cells, and about 20 tornadoes occurred in May and June 2010, he said.

A super cell starts similarly to an ordinary thunderstorm. Warm, moist air rises amidst cooler surroundings and the moisture condensates. In an ordinary thunderstorm, the precipitation creates a cool downdraft that cuts off the warm, moist updraft within about 30 to 45 minutes. The storm dissipates.

A super cell thunderstorm develops when strong upper-level winds allow the warm, moist updraft to continue for up to six hours. The stage is set for the downdraft and the updraft to begin rotating.

But the process that produces a tornado in a super cell thunderstorm is not well understood, Parker said.

For example, strong super cells are not associated with tornadoes, he said. Storms with similar structures may differ in tornado production. And the relationship between near-ground wind fields and structural damage isn’t clear either.

Scientists hope that once the VORTEX2 data is crunched and analyzed and published, some of the questions will be answered, Parker said. Especially head-to-head comparisons of data collected from storms that generated tornadoes and storms that didn’t might be fruitful.

Goals of the VORTEX2 study are to extend the average lead time for tornado warnings from about 13 minutes currently to at least 35 minutes and reduce the false alarm rate, which is currently at about 70 percent.