French police are investigating alleging tampering with national weather forecasting service equipment after a series of unusual temperature readings coincided with suspicious winning bets made on Polymarket.

Data from a Météo-France weather station at Paris’s Charles de Gaulle airport was used to settle bets between online gamblers on what the temperature would be in Paris for March and the first weeks of April.

On a few of the days, there was more than $500,000 (£371,000) in play on these bets. Several traders appear to have made significant profits – three separate wallets made more than $280,000 by betting that the temperature in Paris would reach 19C on 15 April – with the reading unexpectedly jumping by 5C that evening.

The timing of some of these bets has prompted widespread speculation that enterprising gamblers had tampered with the station. At least one wager appears to have been laid just before a temperature spike, resulting in a $21,000 profit for an anonymous user who also has money on the weather in Seoul and Toronto.

On Polymarket Discord channels, anonymous gamblers shared an AI-generated picture of a man with a hairdryer aimed at a weather station next to an airport runway.

“What did you do to the temperature sensor at Paris airport yesterday? Was your weapon of choice a hairdryer or a lighter?” one bettor asked another.

French police confirmed they had received a complaint from Météo-France and the cybercrime division was investigating. The forecasting service told the Financial Times that “physical findings on one of our instruments and the analysis of sensor data” led it to file the complaint.

Polymarket has stopped using the sensor at Charles de Gaulle as a metric and now relies on one at Paris-Le Bourget airport, but did not cancel the contracts or refund the bets.

The expansion of Polymarket, an online betting platform whose investors include a venture capital firm owned by Donald Trump Jr, is stoking concerns that reality – or truth as it is reported – may become increasingly subject to the whims of a nihilistic and growing community of online gamblers.

Bettors threatened an Israeli journalist after he reported a missile hit near Jerusalem, because of the nearly $1m staked on whether Iran would strike Israel on that day.

Gamblers have discussed contacting an independent US thinktank, the Institute for the Study of War, whose maps will determine dozens of active bets on the flux of war on Ukraine’s frontlines – for example, if Russia might take or lose a village or region.

Neither the Institute for the Study of War, the journalist, nor Météo-France have a say in whether their reports become the determining factor for these bets.

Traders and institutional investors, including Goldman Sachs, are starting to use Polymarket data to inform their trades. Because markets on Polymarket are thin, this has led to concerns that small groups of people might be able to manipulate larger markets by laying bets that skew Polymarket’s odds for certain events.

Polymarket was approached for comment.