Highest temperature in London on August 20?

Platform comparison

Market context

The market concerns the single highest temperature reading recorded at London City Airport on 20 August 2026, measured in degrees Celsius via the Daily Observations dataset on Weather Underground. The settlement window closes at midday UTC on that date, meaning afternoon temperature spikes occurring after 12:00 will not factor into resolution. This timing constraint is material: London's warmest readings typically occur between 14:00 and 16:00 during summer months, creating a hard cutoff that excludes peak diurnal heating.

August 20 falls within London's warmest climatological window, with historical daily maxima averaging 23–24°C and the 90th percentile around 27–28°C. Extreme heat days exceeding 30°C occur roughly once per decade in mid-August; the Met Office records show only three occasions since 1990 when London exceeded 32°C in late August. The 0% crowd probability suggests traders are pricing in either a specific expectation of moderate conditions or uncertainty about the precise temperature thresholds embedded in the market's range structure, which remains undisclosed in available documentation.

Cross-platform comparison reveals limited sportsbook engagement with granular weather derivatives; traditional weather betting focuses on binary outcomes (e.g., "will it exceed 25°C?") rather than range-based resolution. Meteorological forecasting skill for specific dates two years ahead remains negligible, with ensemble models showing near-zero predictive power beyond the seasonal norm. Traders should monitor whether the UK experiences a sustained heat dome pattern in summer 2026 or if Atlantic weather systems maintain cooler, unsettled conditions typical of many recent August periods.

Methodology

We track Highest temperature in London on August 20? across the five venues with material prediction-market liquidity. The probability shown is the live Polymarket mid; the comparison rows summarise how each venue treats the underlying contract — fees, KYC thresholds, settlement currency, deposit options. The highlighted row marks the cheapest route into Polymarket's order book.

Resolution & payout

Settlement runs on-chain. Polymarket's contract logic separates YES and NO shares as conditional tokens; at resolution the winning share lifts to $1.00 and the losing one to $0. The outcome input comes from the UMA Optimistic Oracle, which secures against bad resolution with a bond + dispute window.

Once finalised, the smart contract pays USDC to the holders' wallets within minutes — no withdrawal fees beyond Polygon network gas. Kalshi settles in USD via CFTC clearance, Betfair in account currency net of commission, Manifold in play-money mana with no cash-out.

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 Best Prediction Markets. Kalshi charges up to 7% per trade; Betfair Exchange takes 2-5% commission on net winnings.

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.

How fast are USDC deposits?

Polygon credits deposits after 12 confirmations — usually under 30 seconds. Withdrawals follow the same path and land back in your wallet within minutes.

How reliable are the quoted odds?

The YES/NO percentages are the live mid-prices of the Polymarket order book. On deep markets they move every few seconds; on thinner ones you'll see short plateaus.