You're on!
I was reading this article about advances in determining the distance of lightning strikes after a thunder clap. It seems the have developed a device that can determine distance to within a metre and can find strikes that are as close as one kilometre.
Since most world bike events, including the TdF and the Olympics measure distances in metric, i.e. kilometres and metres, some cyclists now have their computers set to metric. This is most useful during a lightning storm because, thanks to this new machine, they can quickly determine if their is a lightning strike danger without the cumbersome conversion to feet, yards and miles.
A portion of the gripping article is attached for your reading pleasure. So is the link.
System Locates Lightning Strikes to Within Meters
A system for determining the locations of nearby lightning strikes from electric-field and acoustic measurements has been developed and built. The system includes at least three receivers, each equipped with an antenna and a microphone. For each strike, the system measures the difference between the times of arrival of the electric-field and sonic (thunder) pulses at each receiver, computes the distance of the strike from the time difference and the speed of sound (about 320 m/s), then uses the distances to determine the location of the strike. The basic concept of this system is thus a variant and extension of the time-honored concept of estimating the distance of a lightning strike from the difference between the times of arrival of the visible flash and the audible thunder.
"Nearby" as used here signifies that the receivers and the lightning strikes of interest are located at distances of the order of 1 km from each other. Older lightning-location systems cover observation areas with radii of the order of 30 miles (48 km), and typically locate lightning strikes with errors of the order of 0.5 km or more; thus, the older systems do not locate strikes accurately enough for purposes of assessing actual or potential damage by lightning to specific structures and pieces of equipment. The developmental system locates strikes to within errors of the order of a meter.
http://www.nasatech.com/Briefs/July00/KSC11992.html