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□ On May 3rd, 1999, all the atmospheric ingredients needed for the creation of large, long-tracked tornadoes came together over the Great Plains. A dry line atop the Oklahoma and Texas Panhandles separated a mass of warm, humid air from dry, cool air slowly encroaching from the west. Weather balloons released across Tornado Alley rose into the air in erratic zigzags, and indication of rapidly shifting winds at different altitudes. The atmosphere was unstable, and by late morning the National Weather Service had upgraded the severe weather risk from slight to moderate.
Around 4pm, weather satellites captured a series of supercell thunderstorms exploding out of the afternoon sky. At 6:20pm, a large funnel descended from the sky near Amber, Oklahoma. The tornado, later dubbed “A9″ on survey maps, rapidly intensified as it thundered northeast through Grady County. Within minutes of touchdown, the storm expanded into a massive wedge more than a half mile wide. Storm chasers captured the tornado as it tore past the Chickasha Municipal Airport and entered an unpopulated area to the northeast.
The mesocyclone that spawned the tornado was exceptionally violent. Low hanging clouds or “skud” swirled around the massive tornado at terrific speeds as large satellite vortices rotated around the main funnel, causing additional damage. Local news stations in Oklahoma City quickly focused their attention on the Grady County storm, and regular programming was interrupted by live broadcasts of the approaching tornado.
The tornado struck little for many miles before taking aim on the small, unincorporated town of Bridge Creek. By the time the tornado reached the town’s first cul-de-sacs it had expanded to a mile in width.
The tornado was at peak intensity as it approached the I-44 Interchange in Bridge Creek. Unfortunately, many of the households in the area were mobile homes with no underground storm shelters. Some residents sought protection in irrigation ditches and culverts beneath roads, though many were seriously injured by the blizzard of flying debris. One young couple was caught outside while running a short distance to their neighbor’s storm cave (Pam, Brown, Kruger et al., 2001). Their bodies were found wrapped in debris more than 200 yards from their destroyed home.
Damage in the Bridge Creek area was among the most intense ever surveyed. Frame homes were swept completely away and mobile homes in the direct path of the storm disappeared without a trace. Aerial imagery around the I-44 Interchange showed a 200-yard wide core of extreme damage in which vegetation was ripped from the ground and trees were stripped of all bark and branches. Surveyors also documented vehicles thrown up to one mile. In total, 12 people were killed in Bridge Creek. The fatality to injury ratio was seven times higher in Grady County than in the Oklahoma City suburbs, a testament to the storm’s incredible ferocity in the area.
The Bridge Creek tornado traveled parallel to the I-44 for much of its life. Had the tornado travelled a half mile farther to the south, it would have spent over 20 miles directly over the freeway and likely killed dozens of motorists. Surprisingly, none of the tornado’s fatalities occurred in vehicles. There were four fatalities, however, in which people attempting to flee were killed while running to their vehicles. Additionally, there were two well-documented deaths beneath freeway overpasses. A third overpass death often attributed to the tornado was actually caused by a separate storm north of Oklahoma City near the town of Mulhall.
The path of the tornado along the I-44 gave the Doppler On Wheels (DOW) an excellent opportunity to stay within close proximity to the tornado for a long period of time. As a result, the DOW was able to thoroughly analyze the storm throughout its mature stage. It is a common misconception that mobile doppler radar “measures” tornadic winds and provides researchers with a single numerical value. Instead, mobile radar analyzes the movement of condensation and debris and calculates a statistical range in which the particle velocity can be estimated.
As the Bridge Creek tornado passed the I-4 interchange, the DOW calculated a velocity that likely fell between 281 and 321mph. The figure, often quoted as 301mph +-20mph, remains the highest radar velocity ever recorded. This is by no means, however, evidence to support that the Bridge Creek tornado was “the strongest tornado ever recorded.” Far less than 1% of all violent tornadoes have been tracked by mobile radar, and of the tornadoes that have been analyzed, only a fraction of their total path lengths were recorded. The Bridge Creek tornado’s unique path adjacent to a freeway gave researchers a rare opportunity, and it is not surprising that the record velocity was calculated given the near perfect circumstances.
Ground scouring indicates that the tornado remained intense as it entered McClain County. The path width narrowed slightly, and the tornado’s appearance changed into a ‘stovepipe’ formation with a wide debris cloud at its base. After remaining parallel to the I-44 for more than 40 minutes, the tornado reached a bend in the freeway and crossed over it, leading to McClain County’s only fatality. A woman who had taken shelter under an overpass with her son was swept away and killed while others who had taken shelter in the same location were injured by flying debris and found plastered in red dirt.
The city of Moore was nearly motionless as the tornado entered Cleveland County. Sirens had been sounding for nearly an hour, and on-air meteorologists had advised viewers in the strongest language ever broadcast to seek shelter or “you will not survive this storm.” Entire rows of tightly packed homes were obliterated as the tornado entered town from the southwest, filling the sky with debris. One of the first housing subdivisions directly impacted by the tornado was Eastlake Estates, located to the south of Westmore High School. While the tornado engulfed a wide area, the extreme damage was confined to a streak 100 yards wide in the center of the damage swath.
Eleven people were killed in Moore, and a further 12 were killed in Oklahoma County, specifically in Del City and Midwest City. A detailed morbidity report concluded that a third of the documented victims were killed in “recommended places”, meaning in an interior room in a frame home. Excluding the deaths in Grady and McClain County, it is probable that most of the victims in the Oklahoma City area had taken appropriate shelter. The intensity of the tornado made survival, even in some well-built homes, difficult. At least two of the fatalities in Moore occurred when vehicles were hurled atop people huddled in their homes.
The tornado was the deadliest in the United States during the 1990’s and remained the single most damaging tornado in history until 2011. Even so, the death toll of 36 people was surprisingly low. Excellent warning, live television broadcasts, good visibility and the tornado’s fairly slow forward speed reduced the number of fatalities. Had the tornado formed two hours later, after dark, the death toll could have easily been twice as high.
Some falsely believed that the Bridge Creek tornado was ‘proof’ that no single tornado could ever again cause over 100 fatalities. This assumption was shown to be terribly wrong in 2011 when an EF5 tornado killed 158 people in Joplin, Missouri. While the Bridge Creek tornado’s death toll was testament to improved forecasting and technology, the storm was, in a sense, perfect from a forecasting perspective. Tornadoes that intensify rapidly near populated areas and tornadoes obscured by precipitation will continue to pose a major threat to cities across the county. A tornado causing over 1,000 fatalities in United States is not just a possibility but, given enough time, a meteorological certainty.
*Bob Webster’s complete aerial photo gallery of tornado damage in Moore and Oklahoma County can be found here. Used with permission.