It was to be the first of 13 warnings issued that evening of May 11, 1982-all with an average lead time of 29 minutes. This distinctive hook-shape is produced sometimes by conventional radar signals reflected from swirling raindrops inside a storm. Within minutes, however, Kendall issued a tornado warning. But the monitor of his 1957-vintage radar revealed no 'hook-echo,” the rare sign of a forming tornado. Kendall already had recognized the classic signs of a severe storm so common in the Oklahoma springtime. Speaking quickly into the telephone, Wilk briefed Lead Forecaster Joe Kendall at the Oklahoma City Forecast Office of the National Weather Service, just 20 miles away. The telltale sign was obvious to the two researchers: rain was spiralling in a tight vortex of wind that in minutes would become a tornado. The adjacent red area revealed rain moving away from the radar. The bright green area identified wind-driver, raindrops moving rapidly towards the radar. Inside the control room of the experimental Doppler weather radar at NOAA's National Severe Storms Laboratory (NSSL) in Norman, Okla., the storm showed up as a color-coded mass on the radar's television screen.Įxamining the monitor, NOAA researchers Don Burgess and Ken Wilk saw the closely spaced red and green areas near the edge of the storm. Some of the energy was reflected by raindrops in the storm back to the radar antenna. The pulses, measuring 10 centimeters (4 inches) in wave length, penetrated a large thunderstorm some 50 miles to the southwest. Steadily, the 30-foot diameter radar dish rotated, sweeping the Oklahoma prairie with a narrow pencil beam of radio frequency pulses. The following article by Don Witten appeared in the Winter 1984 edition of NOAA Magazine. (National Severe Storms Laboratory photo) Above: Research Doppler radar near Norman, OK in 1970, with WSR-57 radar seen to the right.

Underground weather radar nexrad