NORMAN — Oklahoma Watch invited Nancy Mathis, a Tahlequah native and author of a book on the deadly 1999 tornado in Moore, to offer thoughts about Monday’s tornado that struck the city. Mathis’ 2007 book, “Storm Warning: The Story of a Killer Tornado,” explored the causes and effects of the 1999 tornado, as well as the science behind tornado forecasting and protection, all of which remain relevant today.
May 3, 1999, might have passed as an unremarkable spring day in Tornado Alley, with a few run-of-the-mill thunderstorms at first. But, as Oklahomans know, the unusual did happen.
“May 3” is shorthand for a tragic event and needs no explanation when spoken in Oklahoma. An F-5 tornado plowed through the city with devastating violence, claiming dozens of lives. Now we have May 20 and another massive tornado, with obliterated schools, fallen children and the lessons of May 3 to be learned again.
Even the questions are the same, especially: What more can we do to protect ourselves?
Few states are as prone to violent tornados as Oklahoma, especially central Oklahoma. Blame it on location. There is the confluence of cold air off the Rockies and warm, moist air from the Gulf of Mexico, plus a jet stream riling the atmosphere. The invisible boundary separating the warm and cool air is called the dry line, and it’s here where severe weather often begins, especially super-cell thunderstorms that produce the most violent twisters.
Researchers have calculated that on any given day in May, you have a 10 percent chance of seeing a tornado just south of Oklahoma City.
On May 3, 1999, the national Storm Prediction Center issued only a slight chance for severe weather. But thin, cooling cirrus clouds began to part and the sun warmed the ground, which sent more warm air aloft. Such subtleties make forecasting an art. Meteorologists began to upgrade their forecasts. In contrast, on May 20, 2013, it was well known that conditions signaled a major event. The day before, a twister had struck Shawnee.