ASK TOM

Dear Tom,

What is the length of lightning bolts?

— James Torrinson, Chicago

Dear James,

The National Lightning Detection Network, or NLDN, operated by the Vaisala Group, measures the lengths of lightning bolts by utilizing a very high-resolution, threedimensional detection system that records the emission of flashes in the very high-frequency range.

The NLDN has been in place since the early 2000s and has generated some astounding information about the length of lightning bolts.

Meteorologist Ron Holle, a lightning expert with Vaisala, tells us, “The network has measured quite a few flashes over 100 miles long; our current record is 120 miles from a flash that shot from Dallas (Texas) to Ft. Worth. … I don’t think we would have expected that, but there it is!”

Write to: ASK TOM 2501 W. Bradley Place Chicago, IL 60618 asktomwhy@wgntv.com WGN-TV meteorologists Mark Carroll, Steve Kahn, Richard Koeneman, Paul Merzlock and Paul Dailey, plus Bill Snyder, contribute to this page. Hear Tom Skilling’s weather updates weekdays 3 to 6 p.m. on WGN-AM 720 Chicago.