ASK TOM

Chicago Tribune (Sunday) - - CHICAGO WEATHER CENTER -

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 ask­[email protected] 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.

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