French police are investigating possible tampering with a weather monitoring device at Charles de Gaulle Airport in Paris after a Polymarket trader netted thousands of dollars thanks to an unusual temperature spike. Riccardo Milani/AFP via Getty Images hide caption

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Riccardo Milani/AFP via Getty Images

A hair dryer? A lighter? A lucky coincidence?

Authorities in France are investigating possible tampering with a weather monitoring device at Charles de Gaulle Airport in Paris after an unusual temperature spike was recorded around the same time a Polymarket trader cashed in.

An anonymous trader with the username "xX25Xx" has drawn scrutiny from analysts and fellow traders on Polymarket, where people can bet on things like a city's top temperature and other real-world events.

The trader bet $119 that the weather in Paris on April 15 would jump past the equivalent of 64 degrees Fahrenheit, and weather enthusiasts online noticed a sudden spike in temperature on that day.…