French police probe Polymarket Paris weather bet : NPR

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

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Riccardo Milani/AFP via Getty Images

Was it a hair dryer, a lighter, or just luck?

In Paris, authorities are looking into potential interference with a weather monitoring device at Charles de Gaulle Airport. This investigation follows an unusual temperature increase which coincided with a profitable bet by a Polymarket trader.

The trader, known by the username “xX25Xx,” has caught the attention of analysts and other traders on Polymarket, a platform where users can bet on various events, including city temperatures.

The trader wagered $119 on the temperature in Paris exceeding 64 degrees Fahrenheit on April 15. When a sudden temperature spike was observed, the trader gained a profit of $21,398.

The Polymarket trader’s bets before they deleted their account. Accessed via the WayBack Machine.

Polymarket/Screenshot by NPR

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Polymarket/Screenshot by NPR

After local meteorologists determined the temperature spike was not a natural occurrence, the trader deleted their account.

The French weather service, Météo-France, has filed a complaint with airport police concerning potential tampering with their equipment, as reported by the French broadcaster BFM TV.

Météo-France and the airport police did not respond to NPR’s request for comment.

As investigations continue in Paris, online forums of weather enthusiasts and Polymarket traders are speculating about how the temperature was manipulated, suggesting devices like a lighter or a battery-operated hairdryer might have been used.

The anomalous weather spike compared to another weather sensor in Paris.

Bubblemaps

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Bubblemaps

“Love it!” commented Vince, a regular Polymarket weather trader on Discord, “I’ve got to have one of those cordless hair dryers with a cord that connects to a weather station!”

Another Discord user, Sakuku, remarked: “The classic ‘blowdryer with heat setting on the publicly-accessible weather monitoring station near the airport’ scam. It’s a classic.”

The French analytics firm Bubblemaps found that no other weather station reported the temperature spike, and that the Polymarket trader’s winning bet was 20 times larger than their usual wager.

Polymarket did not respond to requests for comment.

Prediction markets like Polymarket and Kalshi allow users to bet on various aspects of modern life, from political statements to military actions and election outcomes.

As these platforms have grown in popularity, stories have emerged of traders going to great lengths to gain an advantage, such as timing the national anthem at the Super Bowl or searching for unreleased record sale announcements on musicians’ websites.

There have also been notable cases of suspected insider trading, including a trader who earned over $500,000 from bets on Venezuelan politics and the timing of an Iran ceasefire announcement. Further back, analysts identified a trader who appeared to have profited from advance knowledge of presidential pardons.

In light of alleged abuses and manipulation within these prediction markets, lawmakers have proposed various measures to regulate the platforms, and several states have initiated lawsuits to classify these apps as gambling enterprises.

The Commodity Futures Trading Commission currently regulates the industry, with the Trump administration taking a lenient approach to these disruptive companies.

The Paris weather bet occurred on Polymarket’s unregulated overseas exchange, accessible to U.S. traders via a virtual private network.

According to Polymarket’s website, they are now using data from a weather device at Paris–Le Bourget Airport instead of relying on the Charles de Gaulle sensor data for settling bets.