Highest temperature in London on July 21?

Platform comparison

Market context

The market is pricing a 1% chance that London's highest temperature on 21 July 2026 will exceed a specific threshold—likely in the upper 30s Celsius or beyond. This settlement relies on the London City Airport weather station, which sits in east London and has recorded temperatures consistently across decades, making it a reliable baseline for extreme heat events in the capital.

London's July climate sits in a narrow band historically. The city's all-time record stands at 40.3°C, set in July 2022 during an exceptional heatwave. More typical July highs cluster between 23–27°C, with readings above 32°C occurring roughly once per decade. The 1% implied probability suggests the market is pricing for an outcome well above the 90th percentile for the date—essentially betting against a repeat of 2022-level conditions or a freak event. This reflects the rarity of sustained extreme heat in London, though climate patterns have shifted the baseline upwards over the past fifteen years.

Traders should monitor the UK Met Office's seasonal outlook and Atlantic weather patterns from May onwards, as summer jet stream positioning determines whether continental heat penetrates northwestward into Britain. The North Atlantic Oscillation and sea surface temperatures in the Atlantic will be critical signals. Any early-summer heatwave across Europe in June would raise the odds materially, as would blocking high-pressure systems anchoring over the British Isles in late July. Current consensus treats extreme heat as a tail event; the value case hinges on whether climate trends and atmospheric dynamics have shifted the distribution further rightward than the 1% odds reflect.

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 Who Will Win 2026, which mirrors the Polymarket order book directly.

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

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 Who Will Win 2026 trigger KYC only above $1,500 of lifetime trading volume; under that you trade pseudonymously with a single wallet address.

How reliable are the quoted odds?

The YES/NO percentages are the live mid-prices of the Polymarket order book. On deep markets they move every few seconds; on thinner ones you'll see short plateaus.