The Joplin Tornado Set-up
Severe thunderstorms aren’t uncommon in the spring, yet on May 22nd, 2011, one storm seemed to catch everyone off-guard in Joplin, Mo.
Although severe thunderstorms may be common in the Midwest, EF-5 tornadoes are most definitely not. The year of 2011 happened to be quite an extraordinary year for severe weather, with more than 1,700 tornadoes reported in the U.S., which included the Super Outbreak of 2011 and six EF-5 tornadoes. More than 500 deaths were directly attributed to tornadoes with more than one-fifth of these occurring in Joplin, Mo., alone. This indicates that it only takes one tornado to cause widespread devastation and fatalities.
So what caused such an intense tornado? A strong low pressure system rotating in the northern Plains is to blame. The low pressure system was able to tap into warm, moist air from the Gulf, while on its backside, cold, dry air was being funneled down.
These two air masses met at an eastward advancing cold front, forming a dry line between high dew points to the east and low dew points to the west. As daytime heating occurred, combined with the lift from the low pressure system, thunderstorms began to form along this line, stretching from northern Wisconsin to southern Texas. At the time of the event, winds were turning with height in the atmosphere, producing the atmospheric spin conducive for severe thunderstorm and tornado development.
A supercell thunderstorm formed just west of Joplin around 4 p.m. CDT and trekked southeastward in contrast to other thunderstorms in the line which progressed mostly eastward and northeastward. The southeastward forward movement of the storm was a good indicator of the strength of the supercell, giving it a high likelihood of producing severe weather.
Eventually, the supercell developed a tight couplet of weak east-west rotation, resulting in a weak Ef-0 tornado. However, the tornado quickly grew in intensity and soon became an EF-5, three-fourths of a mile-wide mammoth. It produced widespread and catastrophic damage to the southern parts of Joplin, before dissipating just east of the city. Such destruction indicates that strong tornadoes can occur in populated areas such as Joplin. Cities must be well-prepared for severe weather events, especially as we near the peak of severe weather season.
