Highest temperature in London on May 22?

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Active sub-markets

Market context

Polymarket is pricing this London City Airport temperature contract as a near-certain low outcome, with the YES side effectively at 0% on the current order book. On Polymarket, users lock USDC on Polygon into conditional tokens that settle against Wunderground’s final London City Airport reading for 22 May, so the key issue is not the citywide forecast but the station-specific high before the 12:00 UTC settlement cut-off. In practical terms, the market is asking whether the day’s peak at EGLC lands in the range already reflected by the book, rather than whether London broadly has a warm afternoon.

For context, late-May London usually sits in the low-to-mid teens Celsius for daily highs, with historical averages around 18°C and only occasional spikes into the high 20s. AccuWeather’s May view for London suggests highs can range far above normal in a warm spell, but WeatherSpark puts the more typical May band much lower, with daily highs rarely exceeding the mid-20s. That matters because a 27°C or 28°C print would be unusual enough to move probability sharply, yet these outcomes are still grounded in late-spring heat patterns rather than extreme outliers. London’s record May extremes, compiled by TORRO, show that low-30s are possible, but they are rare enough to be poor anchors for a day-ahead price.

The immediate catalysts are the Met Office and comparable short-range forecasts, plus any afternoon convective showers or sea-breeze effects that could cap the airport’s high before noon UTC. London City Airport’s coastal position can make it cooler than central London on sunny, breezy days, so traders should watch the station-level forecast rather than the city headline. With resolution tied to Wunderground’s final observation, the only practical dependency is whether the airport’s reported maximum is finalised in the relevant range before the market closes.

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

At resolution the UMA oracle takes over: a proposer posts the outcome with a bond, any token holder can dispute within two hours. Without dispute the result is accepted and the smart contract distributes USDC instantly.

On Kalshi (CFTC-regulated) resolution runs through their in-house clearing engine in USD. Betfair Exchange settles after match end in the account's local currency. Manifold pays no cash — only its in-platform "mana" currency.

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.

Do I need to KYC for this market?

Not under $1,500 of lifetime trading volume. Above that threshold, PolyGram 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.