Two Polymarket accounts are under scrutiny after making approximately $37,000 from weather prediction markets focused on Paris temperatures, following what appears to be a data manipulation at a French airport weather station.
The two prediction markets centered on the highest temperature in Paris on April 6 and April 15, 2026, using data from the Charles de Gaulle Airport Station. French media outlet BFMTV reported that on April 6, the temperature suddenly climbed above 21 degrees Celsius before dropping immediately, resolving the market with one winner taking over $16,000.
Blockchain analytics tool Bubblemaps identified a similar suspicious pattern on April 15. According to the analysts, the weather station recorded around 18 degrees Celsius for most of the day, then briefly spiked to 22 degrees Celsius before falling back to the original reading. The spike was not detected at nearby stations.
"That spike didn't show on nearby stations," Bubblemaps analysts reported, noting that just before the temperature surge, one trader began buying NO shares on "18°C" and subsequently exited with over $21,000 in profit.
Ruben Hallali, a meteorologist, told BFMTV that such temperature variations appear highly unlikely under natural conditions. "Such temperature variations seem very unlikely, especially on these two dates, and over such a short period. We can imagine that an individual with a good understanding of how the sensors work intervened, resulting in temperatures rising by two degrees at the right time, to validate a bet," Hallali commented.
Météo France, the official French government weather agency, has reportedly filed a complaint with the Roissy Air Transport Gendarmerie Brigade, alleging tampering with the operation of its automated data processing systems. The incident adds to growing scrutiny of prediction markets, which face concerns over potential insider trading and gambling law violations.
