Apowerful tornado ripped through College Park, Md., Sept. 24, leaving a path of destruction and killing two University of Maryland students.
The tornado was one of several sighted during a violent storm that descended upon the area. What caused such a large tornado on the East Coast?
Tornadoes require rapid upward motions of air in the atmosphere, accompanied by some spin, according to Environmental Science Prof. Pat Michaels, an expert on tornadoes. In the Midwest, the mixing of dry air coming up from Northern Mexico, warm moist air from the Gulf of Mexico and cold air rolling off of the Rockies create high temperature contrasts, which leads to energetic thunderstorms. The jet stream - long, narrow, high-speed air currents that flow eastward across the country - creates the necessary spin. The mixture of air combined with the effects o_f the jet stream work together to create the conditions for a potential tornado.
The East Coast's tornadoes are somewhat shielded from the mixing of tropical and polar air, in part by the Appalachian Mountains. This means that tornadoes here are rarer, generally weaker and are formed somewhat differently. This type of tornado is called a "low-cloud top tornado," Michaels said.
The type of tornadoes that form, as well as the frequency of formation, depend very much on the season.
Late summer and fall tornadoes on the East Coast generally are caused by an incoming cold front that lifts up warm moist air, creating the upward atmospheric motion needed for twisters to develop.
"We have a fair number [of tornadoes] in July and August," Environmental Science Prof. Bob Davis said. "Those are probably the peak months." A secondary peak occurs in April and May. Some tornadoes also occur during hurricane season - between June and November - as spin-offs of hurricanes coming to shore, but these twisters are usually not very powerful.
The twister that hit College Park was classified as F3 on the Fujita scale, a 0 to 5 scale that gauges the strength of tornadoes. On the Fujita scale, tornadoes are rated based on wind speed and the severity of damage caused. In general, tornadoes of F3 and higher rating hit Virginia only once every two to three years.
According to the National Weather Service, a tornado with a rating of F3 can tear off the roofs and walls of well constructed houses, overturn trains and uproot trees. Most tornado-related deaths occur with storms of rating F3 or higher, and not with less powerful twisters. But for a storm on the East Coast, a rating that high is rare. The last tornado in this geographic area more powerful than the one that hit College Park occurred in 1834, Michaels said.
The Virginia twister
Although tornadoes are less of a concern in Virginia than they are in the Midwest, they still can be extremely dangerous. Tornadoes here have shorter and more erratic path lengths than those in the Midwest. This means that although the tornadoes here aren't usually as large, their motion is often far less predictable, Michaels said.
Certain traits of East Coast tornadoes, such as their size, cause them not to show up as clearly on radar as Midwestern twisters. Therefore, it is more difficult for meteorologists to give people adequate warning time to prepare.
In the Midwest, warning times for tornadoes can range up to 20 minutes. Approaching tornadoes spotted early there are announced with a distinctive siren. A warning saved thousands of lives when a tornado struck Oklahoma City in May 1999. But on the East Coast, the decreased ability to sight twisters on radar reduces the average warning time for a tornado to just seven minutes, barely enough time for people to even find out about the danger, Michaels said.
Dangers are compounded on the East Coast because there are often fewer reliable avenues of escape. In Oklahoma City tornado, many casualties were avoided because many people drove away perpendicular to the path of the tornado, Michaels said. However, he said that in both Charlottesville and the College Park area, none of the roads are straight enough to allow people to escape twisters by driving.
"If you aren't sure you can outrun a tornado at a right angle to it, don't try to outrun it in a car," Michaels said.
Because of these circumstances, Charlottesville residents are advised to seek shelter rather than try to escape in a vehicle.
Many preventable tornado deaths occur because people try to outrun tornadoes, or because they fail to find adequate shelter.
Experts believe the two Maryland students were killed because they decided to wait out the storm in their car. They may have survived the storm had they opted for a more solid shelter.
University precautions
In the event of a tornado, University officials would follow the Emergency Operations Plan, created in cooperation with leaders from the City of Charlottesville and Albemarle County, said University spokeswoman Louise Dudley. The plan calls for the evacuation of threatened areas and activation of an emergency operations center in Zehmer Hall, located off Alderman Road.
In general, the University would hear warnings about the possibility of tornadoes from the state climatologists' office or University Police, Doherty said.
The University Housing Department would take several precautions in the event of severe weather.
"We would make sure students are informed of the situation" through resident staff and e-mail, Chief Housing Officer Mark Doherty said. "We would also make sure the lines of communication were open with police, Facilities Management and other agencies."
Tornadoes often are harder to prepare for than other severe weather emergencies because there is little warning. "This isn't where you have a week to say 'Gee, we have a tornado on the way,'" Doherty said.
The Emergency Operations Plan does call for severe weather drills involving emergency personnel once a year.
"We have not had specific tornado drills in the dorms," Doherty said. "After all that happened at Maryland, do we need to think about that? Absolutely."
The National Weather Service advises heading for internal ground-floor rooms, crouching low and using your arms to protect your head and neck.
But the best way for individuals to protect themselves in the event of a tornado is to just be aware, Michaels said.
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