WMO rules on longest distance and longest duration lightning flashes

he lightning flash over Oklahoma in 2007 covered a horizontal distance of 321 kilometers (199.5 miles). The lightning event over southern France in 2012 lasted continuously for 7.74 seconds, the WMO evaluation committee found.

"Lightning is a major weather hazard that claims many lives each year," said WMO Secretary-General Petteri Taalas. "Improvements in detecting and monitoring these extreme events will help us improve public safety."

It is the first time that lightning has been included in the official WMO Archive of Weather and Climate Extremes, which is maintained by the WMO Commission for Climatology and documents details of records for heat, cold, wind speed, rainfall and other events.

Full details of the assessment are given in an Early Online Release posting of the article published on 15 September. The article will be formally published in an upcoming issue of the Bulletin of the American Meteorological Society.

Dramatic improvements in lightning remote sensing techniques have allowed the detection of previous unobserved extremes in lightning occurrence and so enabled the WMO committee to conduct a critical evaluation.

The WMO evaluation committee judged that the world's longest detected distance for a single lightning flash occurred over a horizontal distance of 321 km (199.5 miles) using a maximum great circle distance between individual detected VHF lightning sources. The event occurred on 20 June 2007 across the state of Oklahoma.