Highest temperature in London on May 25?

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Market context

On 25 May 2026, the highest temperature recorded at London City Airport will determine which range this market resolves to. The settlement window closes at 12:00 UTC that day, with Wunderground's historical data for the station serving as the authoritative source. Current crowd pricing reflects 0% probability across all temperature bands, suggesting either extreme uncertainty about the underlying event or insufficient liquidity to establish meaningful odds.

London's May temperatures typically range between 12–20°C, with historical highs occasionally reaching 25–28°C during warm spells. The Met Office records show May 2022 saw a peak of 24.5°C in the capital, whilst May 2020 reached 29.4°C during an exceptional heatwave. These precedents frame the plausible range: whilst sub-15°C days are uncommon in late May, they occur roughly once per decade; conversely, temperatures above 30°C in May are rare but not unprecedented. The 0% crowd probability likely reflects the market's early stage rather than genuine consensus that no temperature will be recorded.

Traders should monitor Atlantic weather patterns from April onwards, particularly the position of high-pressure systems and any early-season heatwaves affecting northern Europe. The UK Met Office's seasonal outlook and European Centre for Medium-Range Weather Forecasts (ECMWF) ensemble models become increasingly reliable from mid-May. Any significant blocking pattern or tropical air mass advection into the British Isles would shift probabilities toward higher temperature bands. Settlement depends entirely on Wunderground's historical archive accuracy, making data source reliability the key operational risk.

Methodology

Methodologically this overview focuses on on-chain pricing: Polymarket's live mid comes from the Polygon conditional-token order book and settles automatically in USDC. The other three venues — Kalshi, Betfair, Manifold — are listed with their platform attributes, because they operate off-chain and a 1:1 comparison of contract mechanics isn't possible.

Resolution & payout

Settlement is on-chain via UMA Optimistic Oracle. A proposer posts the outcome with a bond, a two-hour dispute window opens, then the smart contract lifts winning conditional tokens to 1 USDC and sends payments to holders' wallets automatically. No withdrawal fees beyond Polygon gas.

Off-chain venues (Kalshi, Betfair, Smarkets) settle in local fiat through bank-side clearing — faster than SWIFT, slower than on-chain. Manifold pays no real cash.

FAQ

Where can I trade this market with the lowest fees?

On PolyGram, which mirrors the Polymarket order book at 0% fees. Kalshi charges up to 7% per trade; Betfair Exchange takes 2-5% commission on net winnings.

Is this market available outside the US?

PolyGram is available in most jurisdictions where Polymarket isn't directly accessible. Polymarket itself is geo-blocked in the US/UK/EU. Always check local regulations.

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 it cost to trade on PolyGram?

Zero. PolyGram routes every order to the live Polymarket order book; the only cost is the Polygon network fee, typically under $0.01 per transaction.