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 , 2:39 PM GMT on March 21, 2007
Storm Warning: The Story of a Killer Tornado, which I reviewed earlier this month, recounts the story of the May 3, 1999 monster F5 tornado that ripped through the southern suburbs of Oklahoma City. In addition to providing an exciting fast-paced narrative of the tornado's rampage, author Nancy Mathis also brings up a number of important lessons learned from this storm, which I detail below. With two strong spring storms capable of trigging tornado outbreaks expected to move through the Midwest U.S. Tuesday and Friday next week, everyone living in Tornado Alley would be wise to pay attention to these lessons learned!
A F-4 tornado rips through Kansas, May 8, 2003. Image credit: wunderphotographer Mike Theiss.
Reasons for the low death toll in the May 3, 1999 tornado
Considering that the May 3, 1999 tornado was the strongest ever measured (302 mph winds), hit a major metropolitan area, and destroyed or damaged over 11,000 buildings, the death toll of 38 was remarkably low. It's worth reviewing the major reasons for the low death toll:
1) National Weather Service Doppler radars. The NWS just completed installation of the new NEXRAD Doppler radars nation-wide in 1998. The NEXRAD radars increased tornado warning time from 5.3 to 9.5 minutes, and roughly doubled the percentage of tornadoes warned for from 30% to 60%. Warning times were as long as 39 minutes for the May 3, 1999 tornado. Mathis notes that the number of tornado deaths in the U.S. was cut in half, to roughly 80 per year, after the NEXRAD radars became operational. It took 20 years for the new radars to get procured, thanks to cost overruns and bureaucratic wrangling. Politicians, NOAA administrators, and private contractors involved during the procurement of the next generation of tornado detection equipment should seek to avoid a similar delay. The procurement process for the NEXRAD radars was a disaster that undoubtedly cost lives.
2) A great warning system. A coordinated warning effort by NOAA's Storm Prediction Center, the local NWS office, local media, and Oklahoma local government personel worked brilliantly. The big money and training pumped into tornado preparedness paid big dividends.
3) A tornado-savvy population. Oklahomans are the most tornado-savvy people in the world. They took warnings seriously, and acted on them. A survey of those injured found that the vast majority knew of the warnings and the tornado, but just did not have a proper place for shelter.
4) Luck. The tornado leveled schools that had already dismissed classes for the day, and a shopping mall that had closed earlier. Had the tornado hit several hours earlier, or late at night when its movement could not have been shown on live TV, the death toll could have been as high as 600, according to a NOAA study.
Highway overpasses are the worst place to shelter from a tornado!
Three people died at overpasses during the May 3, 1999 tornado. The presence of the bridge acts to focus the wind, making it stronger under the bridge. Some drivers abandoned their cars on the Interstate under overpasses, blocking traffic and creating a traffic jam where people were trapped when the tornado swept over. If you're caught in your car on the road and choose to abandon the vehicle, pull off the road and seek shelter in a ditch, not under a highway overpass!
Poor home construction contributed to the deaths and injuries
Tornado fatalities were primarily from those in mobile homes, cars, and homes without shelters. The tornado revealed many homes where builders had failed (illegally) to build up to code. Enforcing existing codes and mandating stronger building codes would have reduced the death toll. This, of course, is not popular with the powerful building industry, since better construction costs more.
Tornado forecasting is still in a primitive stage
A day before the May 3 tornado outbreak, the Storm Prediction Center was only forecasting their lowest alert level for severe weather, a "Slight Risk". The computer models were highly scattered in their predictions, and made significant changes with each new run. Nothing about the outbreak was textbook. Most supercell thunderstorms that spawn tornadoes form along a warm or cold front (or a "dryline" where a sharp gradient of moisture is present). However, none of the first few supercells in the May 3 outbreak were near a front or dryline. The classic clash of warm moist Gulf air with cold, dry Canadian air that usually provides the lift needed for supercells was not present. Researchers have a huge amount of work to do before they understand what causes tornadoes like the May 3, 1999 storm.
I'll be back Friday with a new blog.
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