Highest temperature in London on June 28?

Platform comparison

Market context

The highest temperature recorded at London City Airport on 28 June 2026 is the real-world event this contract resolves to, with the market currently pricing a 0% chance that the temperature will exceed the defined threshold. On Polymarket, this USDC-denominated conditional token sits on the Polygon chain, where the crowd-implied probability of a "YES" outcome is effectively zero, reflecting a consensus that the temperature will remain within the expected range. The resolution hinges on the first data point published by Wunderground for that date, ensuring the on-chain settlement is tied directly to the verified meteorological record.

Historical patterns at London City Airport frame how to interpret this near-zero probability. The warm season typically runs from mid-June to early September, with average daily highs exceeding 67°F (19°C), and the hottest month usually sees peaks well above this baseline. Recent data from 27 June 2026 shows a maximum temperature of 31.1°C at a nearby NW3 station, while Kew Gardens recorded 26.6°C on the hottest day of 2026 so far, according to the Met Office [6]. These comparable cases suggest that while extreme heat is possible, the specific threshold in this market is set conservatively high, making a breach statistically unlikely.

Traders should monitor the Met Office’s seven-day forecast for London City Airport and any sudden shifts in southerly wind patterns, which can drive rapid temperature increases [7]. The primary catalyst is the arrival of a heat dome, often accompanied by falling pressure and low humidity, as seen in the current conditions with 88% humidity and falling pressure at 1012mb [2]. While no specific announcement is scheduled, the dependency remains on the Wunderground data feed publishing the first hourly reading for 28 June, which will trigger the market’s final resolution.

Sources: 1 · 2 · 3 · 4 · 5

Methodology

Methodologically we separate two layers: the live probability (Polymarket mid-price) and the platform attributes (fee, KYC, settlement currency, payment rails). That keeps the comparison honest — a single canonical probability across the row, with the venue-by-venue trade-offs spelt out in the columns next to it.

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

Is this market available outside the US?

Polymarket itself is geo-blocked in the US/UK/EU. Always check the legal status of prediction markets in your jurisdiction before trading.

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.

What does Polymarket cost to trade?

Polymarket itself charges 0% — the only cost is the Polygon network fee, typically under $0.01 per transaction. Off-chain venues like Kalshi or Betfair charge 2-7% commission.

Do I need to KYC for this market?

On Polymarket directly, no — it's wallet-based. Intermediary brokers like Polymarket Legit? trigger KYC only above $1,500 of lifetime trading volume; under that you trade pseudonymously with a single wallet address.