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 resolution mechanism pulls directly from Wunderground's historical weather database for that specific station and date, making this a straightforward observational settlement once the day passes. For programmatic traders, the key is establishing a reliable data pipeline to Wunderground's archive—the platform's API documentation confirms historical records become available within hours of the observation window closing at 12:00 UTC.

London's late May temperatures typically cluster between 18–24°C, though extremes do occur. The Met Office's 30-year climate normals show a mean high of 20.5°C for this date, with recorded highs reaching 28°C in anomalously warm years (notably 2018 and 2020). Examining Wunderground's five-year rolling history for 31 May at this station reveals no readings above 26°C, suggesting the probability distribution should weight heavily toward the 20–24°C bands. Traders using conditional orders tied to seasonal forecasts released in April 2026 can calibrate their positions against the UK Met Office's monthly outlook, which typically becomes available six weeks ahead.

The primary catalyst is the North Atlantic Oscillation phase entering late spring; positive NAO conditions in May historically correlate with cooler, wetter patterns across southern England, whilst negative phases allow warm continental air to penetrate northward. Traders should monitor the European Centre for Medium-Range Weather Forecasts (ECMWF) ensemble runs from mid-May onwards, as these provide the most reliable 10–15 day guidance for the settlement window. The current 0% crowd probability likely reflects uncertainty rather than genuine conviction that extreme heat is impossible.

Methodology

This page is a comparison snapshot: one live quote (Polymarket), four reference venues with their key attributes, and a single execution path — every trade button routes to Polymarket Bot UK, which mirrors the Polymarket order book directly.

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 Polymarket Bot 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?

Polymarket Bot 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.

What does it cost to trade on Polymarket Bot UK?

Zero. Polymarket Bot UK 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.