Highest temperature in London on August 11?

Platform comparison

Market context

On 11 August 2026, the highest temperature recorded at London City Airport will fall into one of several defined ranges. The market resolves using the Daily Observations table from Weather Underground rather than the summary Day High & Low figures, a distinction that matters when intraday spikes occur between official observation windows. For programmatic traders, this means building a data pipeline that polls the specific Wunderground endpoint hourly from dawn onwards, rather than relying on end-of-day summaries that may smooth or lag peak readings.

August temperatures at London City Airport typically peak between 20–24°C, though the 2022 heatwave saw readings exceed 35°C on multiple days. Historical August maxima cluster around 22–23°C in average years, with extremes driven by continental air masses pushing north from the Continent. The current 0% crowd probability suggests either the market has not yet attracted sufficient liquidity or the resolution ranges are set at thresholds few expect to breach. Comparing against the Met Office's 30-year August normals for central London provides a baseline; deviations depend on whether a high-pressure system or Atlantic frontal system dominates that particular week.

Traders should monitor the UK Met Office's extended forecast from late July onwards, particularly any amber or red weather warnings issued 7–10 days before the settlement date. The European Centre for Medium-Range Weather Forecasts (ECMWF) ensemble runs, updated twice daily, offer probabilistic guidance on whether anomalous heat will track into the UK. Any significant forecast shift—such as a sudden upgrade to heatwave conditions—typically triggers repricing in temperature markets within hours of publication.

Methodology

We track Highest temperature in London on August 11? 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.

UK Frequently Asked Questions

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 Polymarket Review UK. 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.

Is Polymarket legal in the UK?

Polymarket is accessible to UK traders but is not UKGC-licensed. It operates under US CFTC jurisdiction. UK residents face no domestic legal prohibition on using it, but UKGC consumer protections do not apply. For UKGC-regulated alternatives, Betfair Exchange and Smarkets offer similar prediction-style markets.

Do I pay tax on prediction market profits in the UK?

UKGC-licensed platform profits (Betfair, Smarkets) are typically tax-free gambling winnings for UK individuals. Polymarket profits involve USDC crypto transactions, which HMRC treats as Capital Gains Tax events. Keep full transaction records and report via Self Assessment if gains exceed £3,000 per tax year.

How do I deposit on Polymarket from the UK?

UK traders typically fund Polymarket via Coinbase UK, Kraken or Revolut — buying USDC with GBP and transferring to a Polygon-compatible wallet (MetaMask, Coinbase Wallet). Polymarket's onboarding walks you through the bridging process. Typical GBP-to-USDC conversion costs 0.5–1%.