The Great Plains Tornado Outbreak of 1999

  • Tracks and intensities of the tornadoes that occurred in central Oklahoma during the May 1999 outbreak. Source: NOAA

    Radar image depicting the supercell storm that spawned the EF5 Bridgecreek-Moore tornado. Source: NOAA

    Satellite image depicting the supercell storms across Oklahoma on 3rd May 1999. Source NASA and NOAA

  • The Great Plains Tornado Outbreak of 1999
    08.05.2014 14:59


    The US Tornado season exploded into action early last week as the first major outbreak of the season struck central and southern portions of the country. 35 people were killed in an area stretching from the Midwest to the Deep South as over 70 tornadoes swept through the region over two days. The outbreak followed the quietest start to any season since records began in 1953, with the first tornado-related fatality occurring at a potentially record late time in the year.

    Fifteen years ago this month, however, Oklahoma was reeling from its most prolific tornado outbreak on record. The event unfolded on 3rd of May 1999 as conditions favourable for severe thunderstorm development came together. These included extreme levels of instability, resulting from the daytime heating of moist surface air streaming north on a strong low level jet stream. Additionally, cooling of the upper atmosphere was taking place with a trough of low pressure approaching from the west. Winds were also strengthening and changing direction with height, providing the high levels of vertical wind shear needed for storm rotation. A moisture boundary to the west, known as a dryline, was then instrumental in forcing the warm, moist air to rise into the upper atmosphere.

    Multiple supercell thunderstorms then developed explosively by late afternoon. These spawned a number of damaging tornadoes as they tracked north-east across Oklahoma, southern Kansas and north Texas through the evening and into the next morning, with a staggering 63 tornadoes touching down in less than 24 hours across the state of Oklahoma alone.

    One of the many tornadoes to strike the state was the infamous EF5 tornado that devastated the towns of Moore and Bridge Creek. A Doppler radar probing the tornado measured a wind speed of 318mph, and the National Weather Service issued its first ever Tornado Emergency as the violent storm tracked north-east towards the heavily populated Oklahoma City Metro Area. The tornado carved a 38 mile-long path of destruction during its 85 minute of existence and became one of the costliest in history.

    Overall the outbreak of May 1999 was responsible for damage to over 8000 homes, with total property damage for the event estimated at $1.5 billion. 46 people were killed and 800 injured, although many hundreds of lives were saved by storm tracking and early warning systems.

    By: Billy Payne