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 settlement mechanism relies on historical weather data pulled from Wunderground's archive for that specific station and date, making this a straightforward factual resolution once the day passes. For traders building automated monitoring systems, the data source is stable and accessible via API; the key operational requirement is confirming the exact timestamp of peak temperature and converting between Celsius and Fahrenheit if your tooling defaults to one unit.

May temperatures in London typically range between 15–22°C, with historical highs occasionally reaching 25–27°C during warmer years. The 0% crowd probability suggests the market may be pricing in either extreme cold or reflect low liquidity rather than genuine expectation of an unusually low reading. Comparable May 31st data from prior years at the same station provides the most reliable calibration; traders should cross-reference Wunderground's historical records for the past decade to establish baseline volatility and identify whether recent climate patterns have shifted the distribution upward.

The Met Office publishes seasonal outlooks and monthly forecasts that typically become more precise 10–14 days before the target date. Traders implementing conditional orders or alert systems should monitor these releases alongside broader European pressure patterns, which influence UK temperatures substantially. The settlement window closes at noon UTC on 31 May, so any automated resolution checks must account for the possibility of late-morning temperature spikes before the window locks.

Methodology

Methodologically we separate two layers: the live probability (Polymarket mid-price) and the platform attributes (fee, KYC, settlement currency, payment rails). The odds column is filled only where we have clean data — that avoids the made-up numbers that get a network demoted when search engines cross-check against the source venue.

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 App 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.

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.

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.