Highest temperature in London on May 22?

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Market context

London City Airport’s highest reading on 22 May will be a late-spring temperature call, with the market effectively pricing in a 0% chance of the YES side and treating the low-20s to high-20s Celsius bands as the main contest. That makes the sub-25°C outcomes the clear favourite, while anything much warmer looks like the underdog path. For context, London’s May climate is usually mild rather than hot: long-run averages put daily highs in the low-to-mid teens Celsius, and even in a warmer-than-normal spell the city is still more likely to land in the 20s than to test extreme heat. The historic ceiling is far above this market’s likely settlement bands, but that is not the useful comparison; what matters is how often a decent southerly surge or bright, dry afternoon pushes the airport above the consensus range.

The main catalysts are the day’s synoptic set-up and the timing of the warmest part of the afternoon, since the market settles on the single highest recorded temperature at London City Airport before the 12:00 UTC window closes. A sunnier, lighter-wind forecast would favour the upper end of the quoted ranges, while cloud cover, onshore flow or a marine layer would pull the result back towards the lower bands. Traders should also watch the Met Office and airport-area observations through the morning and early afternoon, because late changes in cloud cover can matter more than model headlines. Recent market pricing on Polymarket has clustered around 27°C and 28°C, so that remains the consensus zone; if actual station readings stay subdued, the value shifts to the cooler outcomes rather than chasing a warmer tail.

Sources: 1 · 2 · 3 · 4 · 5

Methodology

We track Highest temperature in London on May 22? 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

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.

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.

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.