French Authorities Open Investigation Into Paris Weather Bet Anomaly

French authorities have launched an investigation after a bettor won $34,000 on a weather-based wager, raising concerns about possible manipulation of temperature data at Charles de Gaulle Airport.

The case centres around activity on Polymarket, where users placed high-value bets tied to recorded daily temperatures. Since early April, unusual spikes in evening readings at the airport have aroused suspicions as they coincided with large wagers.

Temperature spikes trigger suspicion

According to Ruben Hallali of climate risk firm Sereno, anomalies were detected on two separate occasions. On 6 April, temperatures rose sharply from 18°C to 21°C before falling again. A second incident on 15 April saw readings jump from 16°C to 22°C within 30 minutes, before returning to prior levels. In both cases, the brief spikes set the official daily maximum temperature, which is the reference point for settlement in weather-based prediction markets.

These movements prompted concerns that the readings may not have been natural. Reports indicate that around $1.4 million in wagers were placed on Polymarket during the affected periods. Online speculation has pointed to the possibility of its sensor being heated with a hairdryer, although no evidence has confirmed this.

Complaint filed as probe begins

Météo-France has formally filed a complaint with law enforcement, including the Air Transport Gendarmerie Brigade and the Bobigny Public Prosecutor’s Office.

The agency highlighted irregularities in both physical observations and recorded sensor data, stating: “In view of physical findings on one of our instruments and the analysis of sensor data, Météo-France was indeed led to file a complaint for alteration of the operation of an automated data processing system with the Air Transport Gendarmerie Brigade of Roissy.”

Airport weather sensors are particularly exposed, relying on direct environmental input and often functioning as single-source data feeds for both aviation systems and external markets. Therefore, their readings can be manipulated with simple tools like portable heaters to settle financial contracts.

Market risks and regulatory pressure build

The incident highlights a structural weakness in prediction markets that depend on isolated data points. A short-lived anomaly can determine the outcome of a contract, creating incentives for manipulation. Analysts have warned that weather-linked contracts are often used to hedge positions in sectors such as energy and agriculture. Distorted data could therefore ripple beyond betting markets into broader financial exposure.

Regulatory scrutiny is increasing across multiple jurisdictions. In the United States, the Wisconsin Department of Justice has recently taken action against platforms including Polymarket, Kalshi, Coinbase and Crypto.com. 

At the same time, the Commodity Futures Trading Commission continues asserting federal oversight, while European authorities have moved to restrict or halt certain forms of trading under the MiCA framework.

Several scandals have also added to the controversy. Authorities charged a U.S Army soldier, Gannon Ken Van Dyke for alleged Polymarket trades on classified information. In early April, the same platform was criticised for allowing bets on the fate of wounded U.S pilots in Iran. Insider trading was also suspected after wagers were made on the U.S military action in Venezuela. 

A weather-based bet win has stirred Paris authorities to investigate recent temperature spikes at the Charles de Gaulle Airport. There are suspicions that people are deliberately tampering with the recording equipment to swing outcomes in their favour on prediction platforms. The results of this investigation will impact the regulation of event contracts going forward.