Highest temperature in London on August 17?

Platform comparison

Market context

The market is pricing the highest temperature at London City Airport on 17 August 2026 at 0% across all ranges, suggesting traders believe no outcome warrants a positive probability. This reflects the inherent difficulty in forecasting specific temperature thresholds nearly two years in advance, where even modest shifts in atmospheric patterns can push readings across range boundaries. The settlement mechanism—drawing from Weather Underground's Daily Observations table rather than summary figures—adds precision but also creates a narrow target that amplifies the challenge of prediction.

Historical August temperatures at London City Airport cluster between 20–26°C on average, though extremes have reached into the low 30s during heatwaves. The summer of 2022 saw temperatures exceed 40°C across parts of the UK, demonstrating that outlier scenarios do occur. The 0% crowd probability likely reflects scepticism about extreme heat rather than confidence in moderate readings; it may instead signal that traders view the market as too uncertain to commit capital, or that the range structure itself fails to capture consensus expectations.

Traders should monitor the Met Office's seasonal outlooks as 2026 approaches, particularly any signals about Atlantic blocking patterns or North African heat transport that could drive August anomalies. The UK's climate trajectory—showing a documented warming trend—supports the possibility of above-historical-average temperatures, yet the current pricing suggests this structural shift has not yet influenced market positioning. Early value may exist in ranges capturing 24–28°C, where historical frequency and climate trends converge.

Methodology

Methodologically we separate two layers: the live probability (Polymarket mid-price) and the platform attributes (fee, KYC, settlement currency, payment rails). That keeps the comparison honest — a single canonical probability across the row, with the venue-by-venue trade-offs spelt out in the columns next to it.

Resolution & payout

Polymarket-based markets settle through the UMA Optimistic Oracle on Polygon. A proposer submits the outcome, a two-hour challenge window opens, and unchallenged proposals finalise the resolution. Payouts settle automatically in USDC the moment the result is final — no bookmaker, no delay.

Kalshi-based markets settle in USD via the CFTC-regulated clearinghouse. Betfair Exchange settles in GBP/EUR net of commission. Manifold is play-money and does not pay out real funds.

FAQ

Where can I trade this market with the lowest fees?

Polymarket is geo-blocked in the US/UK/EU. The easiest 0%-fee broker into the same order book is Who Will Win 2026. Kalshi charges up to 7% per trade; Betfair Exchange takes 2-5% commission on net winnings.

Is this market available outside the US?

Polymarket itself is geo-blocked in the US/UK/EU. Always check the legal status of prediction markets in your jurisdiction before trading.

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's the difference between YES and NO shares?

A YES share pays $1.00 if the event happens, $0 otherwise. A NO share pays $1.00 if the event doesn't happen. The market price between 0¢ and 100¢ is the implied probability.

What does Polymarket cost to trade?

Polymarket itself charges 0% — the only cost is the Polygon network fee, typically under $0.01 per transaction. Off-chain venues like Kalshi or Betfair charge 2-7% commission.