The Illinois State Water Survey played a key role in developing tornado-tracking technology used today to issue warnings of impending severe storms.  While testing radar equipment to measure rainfall rates in 1953, ISWS meteorologists were the first to photograph and document a hook echo, a classic sign of tornado development.

This photo shows the radar depiction of a thunderstorm echo
north of the Survey’s radar at the Champaign Airport. The hook
echo with a tornado extends south from the storm echo.

A hook echo is produced by rain, hail, or debris being wrapped around a thunderstorm. The National Weather Service considers the presence of a hook echo as sufficient to justify issuing a tornado warning.

On April 9, 1953, ISWS radar operations were focused on a large thunderstorm passing north of Champaign.   The radar showed a large hook-shaped echo emerging from the thunderstorm. The echo turned out to be the funnel of a large, developing tornado that moved 54 miles to the east.

This was the first time in the U.S. that a tornado had been detected and photographed by radar. It was a nationally noted event, and helped launch a national research program aimed at tornado detection by radar. The Illinois State Water Survey subsequently designed and developed the nation’s first Doppler weather radar in 1968. It detected the motion of drops and particles inside a storm so that the formation of tornado funnels aloft could be spotted. The U.S. now has a network of Doppler radars used for detecting and tracking tornadoes.