Highest temperature in London on August 21?

Platform comparison

Market context

The market is pricing the highest temperature at London City Airport on 21 August 2026 at 0% probability across all temperature ranges, suggesting the crowd expects either no valid reading or an implicit consensus around a specific band. August in London typically sees highs between 20–27°C, with extremes rare but documented; the record high for the month stands at 36.5°C set in 2022. The 0% reading across all ranges is unusual and likely reflects either a technical issue with market setup or extremely tight clustering around a single outcome that the market structure hasn't captured.

Historical August temperatures at London City Airport show considerable year-to-year variation. The 2022 heatwave pushed readings well above the 30-year average, whilst cooler Augusts have produced highs in the low 20s. The settlement specification—using Weather Underground's Daily Observations table rather than the Day High & Low summary—introduces a precision requirement that could affect edge cases where different sources report marginally different peaks. Traders should note that London's urban heat island effect can create localised variations, and City Airport's riverside location influences its microclimate relative to broader London readings.

The key dependency is the Atlantic weather pattern in late summer 2026. High-pressure systems tracking north of the UK typically deliver the warmest August days, whilst Atlantic lows produce cooler, wetter conditions. The UK Met Office's seasonal outlook and European model consensus in early August 2026 will signal whether continental warmth or Atlantic influence dominates. Any significant divergence from the 20–27°C typical range would likely emerge in forecasts 10–14 days prior to the date, giving traders a clear catalyst window to reassess the current flat probability distribution.

Methodology

We track Highest temperature in London on August 21? 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

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.

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.

Do I need to KYC for this market?

On Polymarket directly, no — it's wallet-based. Intermediary brokers like Who Will Win 2026 trigger KYC only above $1,500 of lifetime trading volume; under that you trade pseudonymously with a single wallet address.