French authorities are investigating potential manipulation of weather data used in online betting on the prediction-market platform Polymarket. The inquiry centers on unusual temperature readings from a Météo-France weather station at Paris’s Charles de Gaulle airport, which were linked to a series of suspicious wagers placed on the platform during March and early April 2026.
On several occasions, more than $500,000 was wagered on bets predicting the daily temperature in Paris. Notably, a sudden temperature increase of approximately 5 degrees Celsius on April 15 coincided with significant profits for a small group of traders. Three separate digital wallets collectively earned over $280,000 by betting that the temperature would hit 19°C. One anonymous user, operating under the name “xX25Xx,” reportedly gained more than $21,000 from a temperature spike to 22°C that occurred around 9:30 p.m. that day, a reading that was not supported by data from nearby stations. Another trader named “Hoaqin” was said to have profited about $14,000.
These unusual trading patterns, coupled with the anomalous temperature readings, have raised suspicions of tampering with the weather sensor. Météo-France conducted a physical inspection of the weather station and analyzed the data patterns, leading the agency to file a formal complaint with French police. The investigation is being handled by France’s cybercrime division.
Within Polymarket’s online communities, some participants speculated about deliberate interference with sensor equipment, sharing images jokingly depicting a man using a hairdryer near a weather station. Questions were raised about whether devices such as hairdryers or lighters were used to affect temperature measurements. Following the complaint, Polymarket ceased using data from the Charles de Gaulle station and switched to a sensor at Paris-Le Bourget, although they did not cancel contracts or provide refunds on affected bets.
Polymarket is an unregulated international platform where users can place wagers on outcomes such as weather conditions. The platform has previously faced allegations that some users attempt to manipulate underlying data to influence contract results. While Polymarket has launched a regulated platform in the United States, its broader international operations remain less supervised.
Météo-France’s concerns highlight challenges at the intersection of automated data collection, online prediction markets, and potential fraud. Authorities in France continue to investigate whether the temperature readings were deliberately altered to benefit certain bettors, while Polymarket has declined to provide official comments on the ongoing inquiry.