Highest temperature in London on July 21?

Platform comparison

Market context

The London City Airport weather station will record a maximum temperature on 21 July 2026, with settlement determined by Wunderground's historical data for that specific location. The market currently shows zero probability assigned to any outcome, suggesting either insufficient trader participation or a technical display issue rather than genuine consensus that no temperature will be recorded.

London's July temperatures have historically ranged between 20°C and 28°C, with the city's record July high of 40.3°C set in 2022 during an exceptional heatwave. The 2022 event remains an outlier; typical July maxima cluster around 23–25°C. City Airport, situated in Newham near the Thames, tends to record slightly cooler readings than central London due to its riverside location and exposure to maritime influence. Traders should calibrate expectations against this baseline: extreme heat above 30°C occurs roughly once per decade, whilst temperatures below 18°C are rare in July.

The UK Met Office issues seasonal outlooks and monthly forecasts that traders can monitor through June and early July 2026. El Niño or La Niña conditions, if present during the settlement window, would influence Atlantic weather patterns feeding into British summer conditions. Notably, the Met Office's long-range guidance typically gains reliability only within two weeks of the target date. Traders currently face a data vacuum; meaningful price discovery will likely emerge only as July approaches and conventional weather forecasting becomes actionable.

Methodology

We track Highest temperature in London on July 21? 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

Settlement runs on-chain. Polymarket's contract logic separates YES and NO shares as conditional tokens; at resolution the winning share lifts to $1.00 and the losing one to $0. The outcome input comes from the UMA Optimistic Oracle, which secures against bad resolution with a bond + dispute window.

Once finalised, the smart contract pays USDC to the holders' wallets within minutes — no withdrawal fees beyond Polygon network gas. Kalshi settles in USD via CFTC clearance, Betfair in account currency net of commission, Manifold in play-money mana with no cash-out.

FAQ

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 Best Prediction Markets. 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.

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.

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.

Do I need to KYC for this market?

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