Highest temperature in London on August 21?

Platform comparison

Market context

On 21 August 2026, the highest temperature recorded at London City Airport will fall within one of several defined ranges. In prediction markets, traders buy YES or NO shares on specific outcomes; a YES share pays out if the event occurs, a NO share if it does not. This market asks traders to predict which temperature bracket will contain that day's peak reading, with the resolution hinging on data from Weather Underground's Daily Observations table rather than summary figures. The 0% crowd probability suggests traders currently view the specific range(s) offered as unlikely to materialise, though the market structure means at least one range must ultimately resolve YES.

London's August temperatures have historically clustered between 20–26°C, with extremes rare but not unprecedented. The Met Office records show that temperatures above 30°C in mid-August occur roughly once per decade in the capital, whilst readings below 15°C are similarly infrequent. The current flat probability distribution across available ranges reflects genuine meteorological uncertainty rather than consensus dismissal of any single outcome.

Traders should monitor seasonal forecasting updates from the Met Office and European weather models as August 2026 approaches. Atlantic pressure systems and potential heat domes over continental Europe will be key drivers; any significant heatwave warnings issued in the weeks prior would shift expectations toward higher ranges. The specific use of London City Airport as the measurement station—rather than central London sites—may yield slightly different readings than commonly cited figures, a technical detail that could affect settlement interpretation.

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

At resolution the UMA oracle takes over: a proposer posts the outcome with a bond, any token holder can dispute within two hours. Without dispute the result is accepted and the smart contract distributes USDC instantly.

On Kalshi (CFTC-regulated) resolution runs through their in-house clearing engine in USD. Betfair Exchange settles after match end in the account's local currency. Manifold pays no cash — only its in-platform "mana" currency.

UK Frequently Asked Questions

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.

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%.