Highest temperature in London on June 25?

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Market context

The real-world event hinges on the peak temperature recorded at London City Airport on 25 June 2026, amid a persistent UK heatwave that recent Met Office forecasts suggest could push daytime maximums near 35°C[1]. Historical data from the warm season, which runs from mid-June to early September, shows average daily highs consistently above 67°F (24.4°C), with July typically being the hottest month[5]. Recent comparable cases, such as the 33.9°C maximum recorded in Hampstead on 23 June 2026, indicate that temperatures in the 30–35°C range are not only plausible but increasingly common during this period[8]. The current crowd-implied probability of 0% for the "YES" outcome appears to be a mispricing, as the consensus leans heavily toward the 30°C and 31°C brackets, which collectively hold 52% of the market weight[1].

Traders should monitor the evolving ensemble model spreads and urban heat-island variability, which introduce meaningful uncertainty around the precise maximum and keep the market-implied distribution centred on 34–36°C rather than locking onto headline forecasts[2]. The Met Office forecast for Wednesday shows a spike to 37°C, while Thursday’s projection drops to 31°C, suggesting rapid volatility that could swing the final reading depending on cloud cover and wind direction[3]. A key catalyst is the persistent high-pressure system driving the heatwave; any shift in this system, potentially announced by the Met Office or BBC Weather, could alter the trajectory significantly[4]. Given the current frontrunner status of 30°C at 27%, value may sit in contrarian positions betting on the 34°C or 35°C ranges, which are currently underpriced relative to the ensemble model’s central tendency[2]. The 34°C outcome holds 28% probability for the following day, hinting that the heat may persist or intensify rather than fade[2].

Sources: 1 · 2 · 3 · 4 · 5

Methodology

This page reviews Highest temperature in London on June 25? across five venues. We show live odds for Polymarket-based markets (sourced from the Polygon order book); for other venues we list platform attributes, since the comparable contracts are not exposed via a public API on every venue. Every CTA points at Who Will Win — the application we operate, where you trade directly against the Polymarket order book at 0% fees.

Resolution & payout

At resolution the UMA oracle takes over: a proposer posts the outcome with a bond, any token holder can dispute within two hours. Without dispute the result is accepted and the smart contract distributes USDC instantly.

On Kalshi (CFTC-regulated) resolution runs through their in-house clearing engine in USD. Betfair Exchange settles after match end in the account's local currency. Manifold pays no cash — only its in-platform "mana" currency.

FAQ

Where can I trade this market with the lowest fees?

On Who Will Win, which mirrors the Polymarket order book at 0% fees. Kalshi charges up to 7% per trade; Betfair Exchange takes 2-5% commission on net winnings.

Is this market available outside the US?

Who Will Win is available in most jurisdictions where Polymarket isn't directly accessible. Polymarket itself is geo-blocked in the US/UK/EU. Always check local regulations.

How does resolution work?

Through the UMA Optimistic Oracle on Polygon: a proposer submits the outcome, a two-hour challenge window opens, and USDC payouts settle automatically once the result is final.

What does it cost to trade on Who Will Win?

Zero. Who Will Win routes every order to the live Polymarket order book; the only cost is the Polygon network fee, typically under $0.01 per transaction.

How fast are USDC deposits?

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