Polymarket bettors bag big win betting on the weather. Now the French meteorological agency is investigating 'tampering'

A bout of terrific Spring weather in Paris or market manipulation?

France’s national weather agency, Météo-France, is investigating precisely this question after filing a complaint with local authorities over allegations its weather data in Paris had been manipulated.

On April 6 and April 15, recording devices at Charles de Gaulle Airport recorded a dramatic spike in temperature in the evening.

Given how striking the rise in temperature — and its quick descent — Météo-France suspects foul play.

“Based on physical findings regarding one of our instruments and an analysis of sensor data, Météo-France has indeed filed a complaint with the Roissy Air Transport Gendarmerie Brigade regarding the tampering with an automated data processing system,” the agency confirmed with DL News.

Meanwhile, a handful of new Polymarket accounts won big betting on the weather in Paris on these two days.

One Polymarket user under the handle of Hoaqin won nearly $14,000 by betting $735 that the temperature in Paris would indeed reach 21 degrees Celsius on April 6. They bagged another $2,200 betting that the highest temperature would not be 18 degrees that same day.

The account was created less than 30 days ago.

Another user, Jiuzhou, turned $500 into more than $3,000 betting that the highest temperature in Paris on April 15 would hit 22.

“What makes the Charles de Gaulle readings so striking is not just the magnitude of the spike, but its signature: a sharp, isolated jump at a single station in the early evening, absent from every neighbouring observation,” Ruben Hallali, meteorologist and CEO of Sereno, told DL News. His company certifies weather data for insurance policies.

What’s more, says Hallali, is how closely this anomaly occurred precisely within the settlement window of a financial bet.

“In 15 years of operational meteorology, that is not something weather does on its own," Hallali said.

Polymarket back in the spotlight

This isn’t the first time Polymarket, one of the world’s most popular prediction markets, has found itself at the centre of manipulation claims.

Digital sleuths are highlighting unusual, ultra-lucky traders in specific markets on these platforms.

Just hours before US special forces captured Venezuelan President Nicolás Maduro in January, a brand-new Polymarket account bet more than $30,000 on his ouster.

The account’s total payout exceeded $436,000, sparking major concern that they had intimate knowledge of the government’s classified military operation.

Lawmakers in the US have since been busy writing draft bills to rein in such activity as these platforms grow in popularity.

Interference

As for the weather sensor in Paris, some have suggested clear interference — namely, from a hair dryer.

Hamali suggests it’s not that far fetch’d.

"Weather stations are designed to measure the atmosphere, not to resist deliberate interference,” he said.

“A portable heat source held near the sensor housing for a few minutes is enough to raise the recorded temperature by several degrees without leaving any obvious trace.”

Polymarket didn’t immediately return a request for comment.

Liam Kelly is DL News’ Berlin correspondent. Contact him at liam@dlnews.com.