Highest temperature in London on May 31?

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Active sub-markets

Market context

The settlement hinges on the single highest temperature recorded at London City Airport on 31 May 2026, measured in Celsius. The crowd currently assigns zero probability to any outcome, suggesting either a technical issue with market initialisation or genuine uncertainty about which temperature band will be hit. Historical May temperatures at this urban location typically range between 18°C and 24°C, though anomalies do occur; the Met Office records show May highs in London have occasionally reached 28°C or beyond during warm spells, with 2020 recording notably elevated readings across the month.

The key variable is whether late May 2026 falls within a broader European heat pattern or tracks closer to seasonal norms. Spring weather forecasting beyond two weeks carries substantial uncertainty, but traders should monitor April and early May 2026 conditions as leading indicators—a warm April often signals sustained warmth into May. The UK Met Office's monthly outlook, typically released around mid-April, will provide the most credible guidance on whether anomalous heat is likely. Additionally, the North Atlantic Oscillation and Atlantic jet stream positioning in late May will influence whether continental warm air reaches the British Isles or Atlantic systems deliver cooler, wetter conditions instead.

The zero probability reading suggests the market may be awaiting initial price discovery rather than reflecting genuine consensus. Historical volatility in May temperatures—ranging from cool 15°C days to warm 27°C+ days within the same month—indicates substantial uncertainty remains justified across multiple outcome bands.

Methodology

We track Highest temperature in London on May 31? on the five venues with material liquidity for prediction markets. Live odds come from the Polymarket Polygon order book — the only source that ships real-time data under an open licence. For Kalshi, Betfair and Manifold we list platform attributes (fee, KYC, settlement, payment) instead of fabricated odds, because their APIs use non-comparable contract definitions.

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 it cost to trade on Who Will Win?

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

How fast are USDC deposits?

Polygon credits deposits after 12 confirmations — usually under 30 seconds. Withdrawals follow the same path and land back in your wallet within 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.