May 3, 1999 is a date forever etched in the memory of every Oklahoman. A series of 70 twisters tore through the state with unprecedented fury, leveling entire towns, killing 37 people, damaging or destroying 11,000 buildings, and racking up $1.2 billion in damage. The most powerful of these storms had the strongest winds ever measured at Earth's surface--302 mph. This F5 monster, 1.8 miles in diameter, ripped through the southern suburbs of Oklahoma City. Nancy Mathis, a veteran journalist and native Oklahoman, has just published a book chronicling this remarkable tornado--Storm Warning: The Story of a Killer Tornado. Mathis intersperses a fast-paced narrative of the armada of 50 storm chasers that tracked the May 3, 1999 tornado, with chapters exploring the history of tornado research, plus biographical information on the scientists who study these great storms. The result is a highly entertaining and informative book.

The book begins with a well-written and chilling account of the 1.8 mile wide F5 April 9, 1947 tornado that smashed Woodward, Oklahoma. Back in those days, the National Weather Service forbid their forecasters from using the word tornado in their forecasts, a practice that continued until 1950. The only weather alarms were sounded by rural telephone supervisors calling each other. Like most tornadoes of that era, the Woodward tornado stuck without warning. The twister killed 181 Oklahomans--the worst tornado disaster in Oklahoma history. Mathis writes:

"The tornado ate prickly sand sage to its roots, grabbed the barbed wire and telephone lines, and wrapped them into twisted strings strewn along the countryside.

One character Mathis follows is on a first date at a local movie theater when the tornado strikes: As he leaned in for a first kiss, the entire theater went black, and a tremendous roar from the winds outside drowned out the protests and rattled the building. The theater held together, but the couple emerged a few minutes later to find 100 blocks of the city destroyed, and much of it in flames. Now that's a memorable first date!

Half of the remainder of the book focuses on the May 3, 1999 tornado, with the other half tracing the history of tornado science. The two themes are interwoven, so that the fast-paced story of the chasers following the storm as it smashes through Oklahoma is interrupted by long, thoughtful chapters discussing such topics as the career of famed tornado scientist, Dr. T. Theodore Fujita (Dr. Tornado). Portions of these chapters had some really fascinating material. For example, Dr. Fujita's life was saved in 1945 when cloud cover over his city prevented the U.S. from dropping the second atom bomb on it. Nagasaki got the bomb instead. Dr. Fujita performed his first damage survey in Nagasaki, which helped him later in his career to develop theories of how thunderstorm downdrafts create similar damage patterns. However, I often found myself skipping over the tornado science chapters to resume the exciting story of the chase. I would then go back and read the portions I skipped over, which didn't detract from my reading experience. Here's an excerpt from the chase portion of the narrative, which uses the live broadcast of local KWTV weather forecaster Gary England for much of the story:

"It's approaching the river," Gary told viewers. "The sirens are going off in Moore. It's moving northeast to the Moore area. This is a long-tracked tornado, potentially deadly. The wind speeds are quite strong now, we fear. You have time, you still have a few minutes in Moore to move to a place of safety, but not much."

The tornado crossed I-44 and the South Canadian River. Dead ahead was Will Rogers World Airport, the region's main civilian airport, where hundreds of people were stranded as the airport waved away aircraft. Nothing could take off or land in this weather. The tornado took a right turn and entered a densely packed neighborhood just before officials evacuated the terminals.

Figure 1. Radar reflectivity image of the May 3, 1999 F5 tornado that devastated Moore, Oklahoma. note the classic "hook" shape of the echo, a common feature of strong (F2 or F3) and violent (F4 and F5) tornadoes. At the time of this image, the tornado was crossing Interstate 44 near the Canadian River, after producing F5 damage in Bridge Creek OK, and before causing more F5 damage in Moore. The bright red colors at the tornado location represent not rain or hail, but the aggregate signature of car parts, pieces of houses, shredded tree branches, dirt and other debris, hoisted thousands of feet skyward by the tornado vortex! Image credit: NOAA Storm Prediction Center.

A criticism I have of the book is that there is no map of Oklahoma City showing the landmarks described in the text, detailing where the storm struck. I had to pull out a road atlas and consult a storm survey map put together by the NWS in Norman to figure out what was going on. The addition of photos of the disaster would have been nice as well. However, the science presented in the book was well done, and was taken from interviews with many of the leading tornado researchers in the world. Overall, Storm Warning is book that everyone who lived through the disaster will certainly want to own a copy of, and one that will appeal to those who enjoy storm stories like The Perfect Storm.

Reasons for the low death toll in the May 3, 1999 tornado
Author Nancy Mathis brings up some good points in the book worthy of further discussion here. 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.

Jeff Masters