Friday, February 20, 2015

Study: Humid Southern cities spawn thunderstorms

Photo by David Selby, Wikimedia Commons
"Hot-and-humid metros in the Southeast can birth more summer thunderstorms than rural areas," Becky Oskin reports for LiveScience. "Researchers marked the location of every thunderstorm born in northern Georgia and northeastern Alabama during a 17-year period. There were nearly 26,000 thunderstorms detected between 1997 and 2013. . . . The was a 5 percent greater chance that thunderstorms would pop up over Atlanta compared with the city's surrounding rural areas, the researchers found."

"Per year, that amounts to two or three more thunderstorms of the pop-up variety," which are harder to forecast, said Northern Illinois University graduate student Alex Haberlie, lead author of the study report. A co-author, NIU meteorology professor Walker Ashley, said "This study presents the first evidence that urban areas birth or initiate thunderstorms more often than the surrounding rural areas on a climatological timescale."

LiveScience reports, "The storm risk was greatest for urban and suburban Atlanta in the late afternoon and early evening during July and August, according to the study, published Jan. 7 in the Quarterly Journal of the Royal Meteorological Society. "The findings would likely hold up in similar hot-and-humid Southern cities, such as Nashville, Tennessee, and Birmingham, Alabama, Haberlie said.

"Thunderstorm births were significantly higher on weekdays than on weekend days," Oskin writes. "This suggests higher pollution levels within the city may play a role. . . . The concrete jungle produces heat, often making cities 2 to 5 degrees Fahrenheit hotter than the surrounding countryside. This extra heat means low pressure can form atop urban areas, with higher pressure in rural areas, sparking convection that can trigger thunderstorms." Also, "Tall buildings may enhance the upward convection that leads to thunderstorms."

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