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Anne Lieb, Roger Kuznia, Computer Assisted Reporting, Fall 1998 |
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Iowa's Tornado History 1950-1998 All the DeBoers wanted to do was enjoy a Saturday afternoon with their three children and granddaughter. That Saturday was 12 years ago--April 26, 1986--and the last time a person was killed in an Iowa tornado. While out milking the cows on his rural Lyon County farm, Ken DeBoer and family spotted a tornado approaching. Thinking they could outrun it, all six jammed into the family's pickup truck and tried to get to safety. The winds of that tornado were classified as F2 on the Fujita scale of 0-5, with 5 being the tornado with the highest winds. F2 winds range from 113-157 miles per hour. The winds are categorized on the Fujita scale on the basis of surveying the damage done to a man-made structure after a tornado has passed over it. This tornado had winds strong enough to send an uprooted fence post into the air and through one of the truck's windows, striking the DeBoers' 4-year-old granddaughter, Joni, in the head, killing her. The post also struck Ken's son, Donald, 15, but he survived. Though 629 tornadoes have since passed since that day in 1986, Joni remains the last person to have lost their life from an Iowa tornado. Tornadoes still strike fear into many Iowans. Analysis of Iowa tornado records from the past 48 years reveals three interesting trends, though where tornadoes strike is completely random. Large county population, more tornadoes? The top five counties reporting the most tornadoes contain some of Iowa's largest cities--Davenport, Sioux City, Des Moines and Ames. County Reported number of tornadoes
Joe Winters, a meteorologist for KCRG-TV 9 News in Cedar Rapids, says the number of tornadoes reported isn't necessarily the number of actual tornadoes occurring in Iowa. The trend found through the computer analysis is just what he expected to find. "In those counties, there's a lot more population and in the other counties there's a lot of rural areas and farmland," Winters said. "There just aren't the eyes out there to report the storms." Jim Meyer, a meteorologist for the National Weather Service in Davenport, expressed a similar opinion. "I am sure early tornado records were somewhat skewed by the fact that tornadoes out in open country just would not be reported, especially if they were smaller," Meyer said. Increased reports of Iowa tornadoes Decade Number of tornadoes
However, the increase isn't because weather patterns have increased in severity over the years. It means technology has gotten better, especially with the advent of NexRad radar, an improved version of Doppler radar. NexRad, which was completely installed in television weather centers and National Weather Service branches across the United States in 1996, detects the motion of the air currents inside the storms. If meteorologists see a twisting motion that has shown the likelihood of producing tornadoes previously, a warning will be issued, Winters said. Before NexRad, the NWS relied heavily on ground spotters for their tornado information, as meteorologists weren't able to detect that movement on the radar screen. "The (old) radar could only see where the rain was and how hard it was falling," Winters said. "It could detect no movement." With NexRad radar's success, the role of the on the ground spotter as the main people to warn of tornadoes has diminished. Before NexRad, Winters estimates that there was a 3 to I ratio of spotter-reported tornadoes to radar-indicated ones. Now with NexRad, the radar is able to predict or report better than spotters. That ratio now is about two radar-indicated storms for every spotter-reported storm, Winters said. Winters said NexRad will be able to detect those tornadoes that go unreported in smaller population areas that ground spotters may have missed. Because where a tornado hits is completely random, Winters expects the numbers of tornadoes to even out for every county in Iowa with their new technology. "I don't think you'll see a general increase of tornadoes," Winters said. "I think the number of tornadoes will top off, as long as the weather patterns don't change." Meyer said satellite technology combined with outgoing technology, such as the Weather Channel, local television and radio stations all help get the word out as soon as possible, ensuring the safety of those people affected. "The public at this time has no reason not to be warned of approaching severe, possibly life threatening weather," Meyer said. Better technology has led to better lead times, or the amount of time the public has warning before a tornado will touch down. The lead time for most tornadoes now is about 10 to 15 minutes, but Winters said the goal would be to get 20 to 30 minutes of lead time. These extra minutes would allow people more time to gather family members together and get to safety. Winters said although lead time is what people want, some people don't heed the warning, especially if warnings were previously issued and no tornadoes resulted. That was the case for residents in Washington on this past May 15, 30 years to the day after Iowa's last F5 tornado. One viewer wrote into KCRG and told Winters this is exactly how she felt. "She said he now realizes even a wasted trip to the basement is better than having a tornado coming through," Winters said. "That's what we hope people will take from that. They aren't issued for no reason at all, but they won't always develop into a tornado." Iowa's most tornado prone months--May and June Though every month of the year has had at least one tornado reported, the months of May and June account for over half of all the tornadoes reported in the 48-year period. The biggest reason for this trend is the position of the jet stream during those months. The jet stream is the narrow band of strong winds circling the earth several miles in the air. "During May and June the jet stream meanders across the Midwest for the most part, which provides energy for the storm," Winters said. Though the temperatures may be hotter in July and August, the jet stream is typically up in Southern Canada during these months, Winters said. "We still can get very hot, humid and some good storms here, but to get the real tornadic activity and big severe storms, you need the energy of the jet stream to make the storms go."
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Date last modified: 12/8/98