The day is the day Benjamin Franklin allegedly flew a kite in a thunderstorm, to prove that lightning was electricity. We’ve learned a lot about thunderstorms since 1752, but our fascination with them has not diminished: who can resist the energy of that crackling drumbeat, angry purple clouds, and fleeting bursts of light?

For nearly 200 years, Oxford aficionados have been measuring thunderstorms. Analysis of this particularly long record was published in the journal Weather and reveals a marked drop in the number of thunderstorms in the Oxford region over the past decade. Oddly enough, the 1920s and 1930s were peak thunder years, with an annual average of 20 thunderous days heard. In contrast, the most recent decade recorded an average of only 8.1 days of thunder per year.

Contrary to popular belief, Stephen Burt of the University of Reading discovered that hot weather and thunderstorms don’t automatically go hand in hand. Analysis of Oxford data shows that particular weather conditions such as “Spanish plume events” – southeasterly winds bringing warm air from the Iberian plateau – are better predictors of stormy days for the south England, and that perhaps the reduction in thunderstorms over the past decade is associated with a reduced frequency of this type of weather.