Highest temperature in London on August 21?

Platform comparison

Market context

London City Airport's weather station will record the highest temperature on 21 August 2026, with settlement determined by the Daily Observations table on Weather Underground rather than summary figures. The market currently prices at 0% YES across all temperature bands, reflecting the typical difficulty in forecasting specific daily maxima more than eighteen months ahead. Polymarket's conditional token structure on Polygon means traders are essentially wagering USDC against the probability that the day's peak temperature falls within their chosen range, with settlement conditional on Weather Underground's primary data source confirming the reading.

Historical August temperatures at London City Airport show considerable variability. The station recorded 32.3°C on 9 August 2022 during an exceptional heatwave, whilst typical August highs cluster between 22–26°C. The Met Office's thirty-year climate normals place the August mean maximum at approximately 23.5°C, though individual days regularly exceed this by 5–8 degrees. This historical spread explains why the market has distributed liquidity across multiple temperature bands rather than concentrating on a single outcome.

Traders monitoring this contract should track the UK Climate Projections and any updates to seasonal forecasting models as summer 2026 approaches. The North Atlantic Oscillation's phase and Atlantic sea-surface temperatures in spring 2026 will provide early signals for whether August conditions favour above or below-normal temperatures. Additionally, any significant changes to Weather Underground's London City Airport station instrumentation or methodology could affect how the Daily Observations table records data, though such changes are typically announced in advance by the Met Office.

Methodology

This page is a comparison snapshot: one live quote, four reference venues with their key attributes, and a single execution path — every trade button routes to Polymarket Alternative UK, which mirrors the Polymarket order book directly.

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

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 Alternative 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%.