Tuesday, April 9, 2013

First Tornado Hook Echo Observed 60 Years Ago Today

Today thunderstorms and tornadoes are routinely tracked using weather radar, and in fact anyone with a computer or smart phone can pull up the latest radar images for their area.  As you might surmise, this wasn't always the case.  After World War II surplus radars were being used to study thunderstorms and precipitation. The Illinois State Water Survey, a state agency on the University of Illinois campus, was in the beginning years of a weather research program at the time, a program that continues today. It was during a project conducted by the Water Survey that the now classic "hook echo" radar signature radar was first discovered and photographed in detail. As with many scientific discoveries, it was a serendipitous event.

Meteorology building at Willard Airport and the radar used
to detect the hook echo.
In the late afternoon and early evening hours of April 9, 1953 scattered thunderstorms were moving eastward across central Illinois. At the University of Illinois Willard Airport located a few miles south of Champaign, the Illinois State Water Survey was operating a radar collecting rainfall data for a project to determine the utility of radar for the measurement of precipitation amounts. The radar was a modified 3-centimeter wavelength radar that had been used as an airborne surveillance system installed aboard U.S. Naval aircraft in World War II. A rain gauge network had been established in east-central Illinois to provide ground truth for the radar-indicated amounts.  That day, radar engineer Donald Staggs and an assistant were working at the radar. The radar was only operated as needed for this project, and the normal procedure was to turn off the radar after precipitation had passed through the rain gauge network.  However, on that afternoon Staggs noticed the peculiar radar echo with the thunderstorm and thought “I wonder if that might be a tornado.”  Ten minutes later he received a phone call from a woman who lived just north of Champaign.  She wanted to know if he was seeing "the twister that just destroyed my barn" on radar. At that point he knew that the hook echo might just indicate a tornado and kept tracking it and photographing the radar display as the storm moved into Indiana.  This distinct tornado echo, which was observed near the southwest edge of the associated thunderstorm, contained the tornado funnel.

The first hook echo identified and photographed on radar.

Although Staggs recognized the unusual nature of the radar echo and the possibility of a tornado, positive identification was not made at the time of the radar tracking.  Only when the radar film was developed the next day did the scientists realize that the distinctive hook echo was the signature of the tornado reported the afternoon before.  Field surveys confirmed the tornado, which was eventually rated an F3.

The tornado moved east and dissipated just over the Indiana state line. It had a path of about 54 miles, and destroyed eight homes and damaged 72 others. There was one fatality in Vermilion County, Illinois from the storm.

A view of the tornado on April 9, 1953 taken from near Royal, Illinois.
Tornado photograph taken by Ernie Kienietz, provided by Scott C. Truett

The original report on this historic event is available online, and contains a description of the weather conditions that day, information on the weather radar, and the results of the field survey of the tornado damage, including photographs.  It's a fascinating piece of weather history.  You can read it at the following link.

Study of an Illinois Tornado Using Radar, Synoptic Weather and Field Survey Data, Illinois State Water Survey Report of Investigation 22, Urbana, IL by F.A. Huff, H.W. Hiser, and S.G. Bigler. 1954 

In the report's conclusion, the authors of the report speculated that with more collection of tornado radar data, "...it may be possible to establish radar storm warning systems in tornado areas to reduce loss of lives, and to some extent property damage."  This discovery did, in fact, launch a national research program aimed at tornado detection by radar.  In 1962 the National Severe Storms Laboratory was formed out of the National Severe Storms Project, conducting research on the detection of storms with radar. Today, there are 164 weather radar sites across the U.S. that scan the skies 24/7.

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