Highest temperature in London on July 7?

Platform comparison

Market context

The highest temperature recorded at London City Airport on 7 July 2026 is the real-world event this contract tracks, with current Polymarket pricing showing a 0% probability that the peak will hit exactly 31°C. On the Polygon network, this conditional token is priced in USDC, reflecting the market’s view that the specific threshold is unlikely despite the intense heatwave gripping southern England today.

Historical data frames this low probability: while London’s average July high is 23°C, Met Office records confirm heatwaves frequently push temperatures above 30°C, with a record 40.2°C hit at Heathrow in July 2022 [2]. However, current forecasts for 7–9 July predict highs around 34°C, which is extremely rare for London and suggests the peak may exceed 31°C rather than land precisely on it [1]. This discrepancy between a likely high peak and the exact 31°C resolution point explains the zero-per-cent YES price.

Traders should monitor the Met Office’s hourly updates for London City Airport and the timing of incoming thunderstorms, which could disrupt the afternoon heat and cap the maximum temperature [1]. The resolution depends entirely on Wunderground’s official daily maximum, so any shift in storm timing between 11:00 and 15:00 BST will be critical [1]. Recent forecasts indicate a dramatic weather pattern with heavy downpours and lightning increasing later in the day, potentially lowering the peak before the settlement window closes [1].

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

Where can I trade this market with the lowest fees?

Polymarket is geo-blocked in the US/UK/EU. The easiest 0%-fee broker into the same order book is PolyGram. Kalshi charges up to 7% per trade; Betfair Exchange takes 2-5% commission on net winnings.

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.