Highest temperature in London on August 20?

Platform comparison

Market context

London's weather on 20 August 2026 remains uncertain, with meteorological forecasting at this distance inherently constrained by atmospheric variability. The current crowd assessment of 0% probability across all temperature ranges suggests either extreme confidence in a specific outcome or insufficient trader participation to establish meaningful odds. August typically brings London's warmest conditions of the year, with historical daily maxima frequently ranging between 20–25°C, though heat waves occasionally push readings above 28°C. The 2022 heat event saw London exceed 40°C, demonstrating the tail-risk potential for exceptional temperatures during summer months, albeit rarely.

Traders monitoring this market should track the Met Office's seasonal outlooks and any emerging climate patterns in late July and early August 2026. The resolution mechanism's reliance on Weather Underground's Daily Observations table—rather than summary figures—introduces a technical dependency worth noting; historical discrepancies between observation-level data and day-high summaries occasionally occur due to station calibration or recording intervals. The London City Airport station, situated in East London, may record slightly different maxima than central London or other monitoring points, a distinction material to resolution outcomes. Atmospheric pressure systems developing in the Atlantic during mid-August will be the primary driver of temperature trajectories; traders should monitor extended forecasts from 10–14 days prior to the settlement date for meaningful signal.

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%.