Highest temperature in London on July 21?

Platform comparison

Market context

On 21 July 2026, the highest temperature recorded at London City Airport will fall into one of several defined ranges. The market currently shows 0% implied probability across all outcome brackets, suggesting either minimal trading activity or genuine uncertainty about which range will ultimately contain the day's peak reading. Wunderground's historical data for this station serves as the sole arbiter, with settlement dependent on the recorded maximum for that specific date.

London's July temperatures have historically clustered between 20°C and 28°C, though extremes outside this band occur irregularly. The summer of 2022 saw UK temperatures exceed 40°C in some regions, yet London City Airport recorded 32.1°C on 19 July that year—a useful benchmark for assessing tail-risk scenarios. Comparable July days at this station typically peak in the mid-to-high 20s, with readings above 30°C representing roughly the 90th percentile. The zero probability reading across all brackets suggests the market has not yet attracted substantive trader participation rather than reflecting genuine consensus on outcome likelihood.

The Met Office publishes extended forecasts approximately two weeks ahead, with meaningful refinement occurring five to seven days before settlement. Traders should monitor late-June and early-July seasonal patterns, as these often indicate whether July 2026 will track toward cooler or warmer-than-average conditions. Any significant heat-dome formation across northern Europe in the preceding weeks would shift expectations materially upward. The settlement window closes at midday on 21 July, allowing only morning-of adjustments based on real-time observations.

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

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

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 UK. Kalshi charges up to 7% per trade; Betfair Exchange takes 2-5% commission on net winnings.

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'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.

Do I need to KYC for this market?

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