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 fall into one of several defined ranges. The market currently prices all outcomes at 0% probability on-chain, suggesting either a technical issue with the USDC/Polygon conditional token setup or minimal liquidity across all temperature brackets. Traders settling positions will need to verify the Wunderground historical data feed for that specific date once the settlement window opens, with resolution tied to the single highest reading captured across all hours at the EGLC station.

London's late May temperatures typically cluster between 18–22°C, though extremes have occurred. The 31 May record high stands at 27.8°C, set in 2020 during an unseasonable warm spell. Historical May data from the Met Office shows that temperatures exceeding 25°C on this date occur roughly once per decade, whilst readings below 15°C are similarly rare. The current flat probability distribution suggests traders are either awaiting clearer market mechanics or treating this as a genuine toss-up across multiple temperature bands.

The primary catalyst remains the UK Met Office forecast, which typically publishes extended outlooks 10–14 days ahead of the settlement date. Late May weather patterns depend heavily on Atlantic pressure systems and whether high-pressure ridges establish over the British Isles or remain displaced northward. Any significant heatwave warnings issued in late May 2026 would shift trader positioning toward higher temperature ranges; conversely, unsettled low-pressure systems tracking across the UK would favour cooler outcomes. Traders should monitor the Copernicus Climate Change Service seasonal forecasts issued in April 2026 for early signals of anomalous warmth.

Methodology

This page reviews Highest temperature in London on May 31? across five venues. We show live odds for Polymarket-based markets (sourced from the Polygon order book); for other venues we list platform attributes, since the comparable contracts are not exposed via a public API on every venue. Every CTA points at Kalshi UK — the application we operate, where you trade directly against the Polymarket order book at 0% fees.

Resolution & payout

Settlement runs on-chain. Polymarket's contract logic separates YES and NO shares as conditional tokens; at resolution the winning share lifts to $1.00 and the losing one to $0. The outcome input comes from the UMA Optimistic Oracle, which secures against bad resolution with a bond + dispute window.

Once finalised, the smart contract pays USDC to the holders' wallets within minutes — no withdrawal fees beyond Polygon network gas. Kalshi settles in USD via CFTC clearance, Betfair in account currency net of commission, Manifold in play-money mana with no cash-out.

FAQ

Where can I trade this market with the lowest fees?

On Kalshi UK, 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?

Kalshi UK 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.

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.

Do I need to KYC for this market?

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