Highest temperature in London on August 20?

Platform comparison

Market context

On 20 August 2026, the highest temperature recorded at London City Airport will fall within one of several defined ranges. The market resolves using the Daily Observations table from Weather Underground rather than the Day High & Low summary—a distinction that matters when intraday temperature spikes occur outside peak afternoon hours. For programmatic traders, this specificity means building a scraper that targets the correct data table rather than relying on API endpoints that may aggregate differently.

London's August temperatures have historically clustered between 20–26°C, with extremes reaching 28–30°C during heat waves. The Met Office records show that sustained high-pressure systems pushing northward from continental Europe drive the outlier events; the summer of 2022 saw multiple days exceed 30°C, whilst cooler Augusts remain common. Current crowd probability sitting at 0% YES suggests the market is pricing in either a narrow resolution band or a baseline expectation that August 2026 will not produce an exceptional peak—a reasonable stance given that single-day forecasts two years out carry substantial uncertainty.

Traders monitoring this market should track seasonal weather pattern indices from the Met Office and European Centre for Medium-Range Weather Forecasts (ECMWF) as August 2026 approaches. The North Atlantic Oscillation and jet-stream positioning in late July will signal whether high-pressure dominance is likely. Conditional order logic could be structured to activate bets once ensemble forecasts converge within 10 days of the settlement date, when model skill improves materially and the probability distribution tightens around observable atmospheric setup.

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

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.

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%.