Highest temperature in London on August 18?

Platform comparison

Market context

On 18 August 2026, the highest temperature recorded at London City Airport will determine this market's settlement. The contract currently prices at 0% across all temperature bands, suggesting traders are either awaiting historical data or treating this as a placeholder ahead of the settlement window. The resolution mechanism relies specifically on Weather Underground's Daily Observations table rather than summary figures, a distinction that matters when automated systems or manual recording discrepancies arise between data sources.

London's August temperatures have historically ranged between 18–27°C, with the city's record August high standing at 36.4°C set in 2022. The 0% crowd probability reflects uncertainty about which temperature band will ultimately contain the day's peak reading, not scepticism about whether a temperature will be recorded. Comparable August markets on Polymarket have typically seen probability mass distributed across the 20–26°C range for London, with tail outcomes (below 18°C or above 28°C) receiving minimal backing unless seasonal forecasts shift dramatically.

Traders should monitor the Met Office's long-range forecasts as August 2026 approaches, particularly any signals about high-pressure systems or Atlantic weather patterns that could drive anomalous heat. The UK's summer weather in recent years has shown increased volatility, making historical averages less predictive than they once were. Settlement depends entirely on the Weather Underground data feed from London City Airport, so any station maintenance or data transmission issues during 18 August could affect resolution clarity, though Wunderground's redundancy protocols typically mitigate such risks.

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

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.

FAQ

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.

What's the difference between YES and NO shares?

A YES share pays $1.00 if the event happens, $0 otherwise. A NO share pays $1.00 if the event doesn't happen. The market price between 0¢ and 100¢ is the implied probability.

What does Polymarket cost to trade?

Polymarket itself charges 0% — the only cost is the Polygon network fee, typically under $0.01 per transaction. Off-chain venues like Kalshi or Betfair charge 2-7% commission.

How fast are USDC deposits?

Polygon credits deposits after 12 confirmations — usually under 30 seconds. Withdrawals follow the same path and land back in your wallet within minutes.

Do I need to KYC for this market?

On Polymarket directly, no — it's wallet-based. Intermediary brokers like PolyGram trigger KYC only above $1,500 of lifetime trading volume; under that you trade pseudonymously with a single wallet address.