Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 3:47 PM GMT on April 25, 2014
It's well-known that one should avoid mobile homes during a tornado, as their relatively flimsy construction and tendency to roll when exposed to high winds leads to numerous deaths each tornado season. The majority of tornado deaths occur in mobile homes for this reason, but tornado experts have long wondered why mobile home parks seem to get disproportionately more tornado strikes than other residential areas. New research by Purdue University researchers Olivia Kellner and Dev Niyogi suggests that "transitions zones"--areas where dramatically different landscapes meet, like where a city fades into farmland, or a forest meets a plain--are more prone to tornado touch downs. Since mobile home parks are often located at the edge of built-up areas, they may actually get hit more often.
Figure 1. Damage to 2-year-old C.J. Martin's mobile home park near Evansville, Indiana due to a November 6, 2005 tornado. Twenty people. including C.J., died in the F3 tornado that devastated his Eastbrook Mobile Home Park in Evansville. The storm hit at 2am, when many residents were asleep and didn't hear the tornado sirens. C.J.'s mother, Kathryn Martin, pushed lawmakers to adopt a bill requiring all mobile homes in Indiana to have a weather radio with a tone alert system, which could have saved many lives in the mobile home park that night. C.J.'s Law was signed into law by Indiana governor Mitch Daniels later that year. Image credit: Paducah, KY NWS.
The researchers studied where tornadoes touched down in Indiana between 1950 and 2012, and found that 61% of tornado touchdowns occurred within 1 kilometer (about 0.62 mile) of urban areas, and 43% fell within 1 kilometer of forest. Kellner said the percentages suggest that certain locations may increase the likelihood of tornado touchdowns due to increased "surface roughness"--an abrupt change in the height of land surface features, which can stretch or squash a column of air, increasing its rate of spin, which could contribute to the formation of tornadoes. Forecasters and city planners may need to pay closer attention to these "transition zones" to better understand tornado risks, said Olivia Kellner, doctoral student in the Department of Earth, Atmospheric and Planetary Sciences in a press release. "There are still many unanswered questions about tornado climatology, but what we're finding is that there may be a relationship between the Earth's surface and the atmosphere that contributes to where tornadoes tend to touch down." The study also found that tornado touchdowns in urban areas tend to occur at about 1 and 10 miles from the city center. Kellner said these "rings" of increased tornado activity could be related to how cities are developed. "Cities impact the surrounding climate in terms of regional airflow and temperature," she said. "The size of cities, what they're made of and the heat they produce are factors that could affect the microclimate."
Original study: Kellner, O., and D. Niyogi, 2014, Land-surface Heterogeneity Signature in Tornado Climatology? An Illustrative Analysis over Indiana 1950-2012, Earth Interactions, doi: http://dx.doi.org/10.1175/2013EI000548.1
Figure 2. Severe weather outlook for Sunday, April 27, 2014, as issued on Friday, April 25, by NOAA's Storm Prediction Center.
Weekend tornado and severe weather outbreak coming for the Plains
A multi-day severe weather event is expected Saturday, Sunday, and Monday across the Central U.S., as a strong low pressure system will spawn supercell thunderstorms capable of generating large hail, damaging winds, and a few strong tornadoes. The most dangerous day appears to be Sunday, and NOAA's Storm Prediction Center (SPC) has issued their "Moderate Risk" forecast of severe weather over portions of Arkansas , Oklahoma, Texas, and Louisiana that day. The action will begin Saturday afternoon along a swath from Central Texas northwards into Oklahoma and Kansas, but at present, Saturday's threat warrants only a "Slight Risk" classification from SPC. This weekend's severe weather outbreak has the potential to be the most dangerous one of this relatively quiet 2014, which has yet to spawn a killer tornado. The relatively cool and dry weather across Tornado Alley so far this year has led to no EF-3 or stronger tornadoes as of April 24, which is a record-long wait since modern tornado records began in 1950. According to tornado historian Tom Grazulis' book, Significant Tornadoes 1680-1991, "serious efforts" to document all tornadoes began in 1953, which was the first full year of tornado watches issued by the U.S. Weather Bureau, now the National Weather Service.
I'll have a new post on Monday. Have a great weekend, everyone!
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