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A strange weather market case has put Polymarket back in focus after reports alleged that a trader manipulated a Paris temperature reading used to settle bets.
Good to Know
A Paris weather market on Polymarket has drawn attention after allegations that a trader used heat near a temperature sensor to help settle a longshot bet in their favor.
The market tracked weather data from a Météo France sensor near Charles de Gaulle Airport. According to posts shared on social media and reporting by The Guardian, a person may have used a portable heating device, possibly a hair dryer, to raise the reading long enough for 22°C to become the winning outcome.
One social media user summed up the case by saying:
“A hair dryer at a Paris airport broke Polymarket weather markets & made someone $34,000 richer.”
The trader reportedly bought cheap shares on a 22°C outcome for April 15, even though the Paris average high for the month sat closer to 16°C. The same person allegedly used a similar method on April 6. Together, the wins reportedly reached $34,000.
French police confirmed that they are investigating after Météo France filed complaints over suspected tampering. The case remains open, so the full picture is still not final.
Weather markets can draw real money. Paris temperature markets have produced more than $185,000 in daily trading volume, while similar Kalshi markets often reach six figures. Low-priced longshot contracts can trade near 1 cent, giving bettors a large payout when an unlikely result lands.
Polymarket has reportedly changed the Paris weather market to a different reference station after the suspected manipulation. Still, the case shows how prediction markets can run into trouble when a settlement source can be physically accessed.
The same issue has appeared in less dramatic form elsewhere. New York snowfall markets caused anger earlier in the year after some parts of the city saw more than 12 inches of snow, while the Central Park reading used for settlement came in lower. Under the market rules, “No” bettors won.
Prediction markets often sell speed, open pricing and public odds as strengths. Yet weather markets also rely on very specific measurement points. When traders understand those details better than casual users, the playing field can feel uneven.
Polymarket rules also ban trading when a user has enough authority or influence to affect the outcome of an event. Its terms prohibit:
“Entering, or attempting to enter, any buy or sell order if you hold a position of authority or influence sufficient to affect the outcome of the event underlying such Contract, or if you have been directed or solicited to enter such order by a person who holds such a position of authority or influence.”