Highest temperature in London on May 31?

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Market context

On 31 May 2026, the highest temperature recorded at London City Airport will determine which range this market resolves to, with settlement occurring on-chain in USDC at 12:00 UTC. The resolution source is Wunderground's historical weather database for that specific station, which captures intraday highs across all recorded times. Traders should note that London City Airport sits in East London near the Thames estuary, making it representative of central London conditions rather than suburban or rural readings.

May temperatures in London typically range between 15–22°C, with historical highs on 31 May clustering around 20–24°C over the past two decades. The 0% crowd probability suggests the market may be pricing in either an unusually cool spell or a technical issue with order placement; May 31st rarely sees extreme heat in London, though the 1976 drought and occasional warm continental air masses have produced readings above 25°C in late May. Comparable years show that settled high-pressure systems moving north from the Mediterranean can push temperatures into the mid-20s, whilst Atlantic low-pressure systems keep readings closer to 16–18°C.

Traders monitoring this contract should track the Met Office's extended forecast for late May 2026 and European weather model consensus (ECMWF, GFS) released in the weeks prior. Jet stream positioning and North Atlantic Oscillation phase will influence whether warm air advection or cooler maritime conditions dominate. Any significant deviation from the 30-year climatological mean for that date warrants position adjustment, particularly if high-impact weather systems are forecast to cross the UK during the settlement window.

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 BTC Prediction, 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.

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 BTC Prediction?

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

Do I need to KYC for this market?

Not under $1,500 of lifetime trading volume. Above that threshold, BTC Prediction triggers a quick verification flow that finishes in minutes.

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.