NOAA Finds Fewer Days Featuring Tornadoes, But Increased Prevalence Of Clusters

Chuck Bednar for redOrbit.com – Your Universe Online
Tornado activity in the US has remained fairly constant since the 1970s, but the number of days featuring them has decreased, meaning that twisters are more likely to come in clusters now than in the past, according to new research published Friday in the journal Science.
As part of the study, experts from the US National Oceanic and Atmospheric Administration (NOAA) reviewed records of all but the weakest tornadoes that occurred in the US from 1954 and 2013. They found that the amount of days featuring multiple cyclones had increased in recent years, and as a result, communities should prepare for an increased number of catastrophes from these damaging funnel-shaped vortexes of wind.
“Concentrating tornado damage on fewer days, but increasing the total damage on those days, has implications for people who respond, such as emergency managers and insurance interests,” lead investigator Harold Brooks, a research meteorologist with the NOAA National Severe Storms Laboratory in Norman, Oklahoma, said in a statement Thursday. “More resources will be needed to respond, but they won’t be used as often.”
The study found that, during the 1970s, there were approximately 150 days per year in which there was at least one tornado. Currently, however, that figure has dropped to an average of roughly 100 days per year, according to USA Today reporter Doyle Rice. However, over that same period, the number of days on which at least 30 cyclones were spotted increased from 0.6 days per year in the 1970s to nearly three days per year in the 2000s, he added.
Reuters reporter Will Dunham added that the study also found eight of the 10 days with the most tornadoes since 1954 have taken place since 1999, and half of them have occurred over the past four years. In fact, the study found that there were days featuring 115, 73, 53 and 52 tornadoes in 2011 alone, according to Dunham.
Brooks said that he and his colleagues are not certain why tornadoes are becoming more concentrated on a reduced number of days, but that it could be connected to changes in climate and weather patterns. Co-author Patrick Marsh, a meteorologist at the NOAA’s Storm Prediction Center, told Reuters that there was a “circumstantial argument” that climate change had played “at least some role in the tornado changes.”
The study also revealed that there has been an increased variability in the starting date of spring tornado season, with more early starts and late starts occurring in recent years, according to NOAA. Between 1954 and 1997, tornado season started between March 1 and April 20 ninety-five percent of the time, the agency said. However, over the past 17 years, tornado season between those two dates happened just forty-one percent of the time.
“The study’s results are a first step toward understanding the relationship between changing tornado activity and a changing climate,” the agency, which only analyzed data for tornadoes rated EF1 or higher on the Enhanced Fujita Scale, said. “The next step will be for climate scientists and tornado researchers to work together to identify what specific large scale pattern variations in climate may cause, or are related to, clustering of tornado activity.”
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