Highest temperature in London on August 2?

Platform comparison

Market context

London’s **2 August high** is being priced as a fairly narrow summer-range call rather than a binary heatwave bet, with the market currently leaning to **27°C** at 52% and **26°C** next at 26%, while the crowd has **0%** on the contract settling at the lowest bucket. That is broadly consistent with platform-level forecasts that cluster around the high-20s: Polymarket’s own event page cites Met Office guidance for a 27°C daytime maximum under strengthening high pressure, light winds and southerly flow, while other weather models shown in the same comparison space span roughly 26°C to 28.5°C. [1][7]

The useful comparison here is with London’s recent warm spells, which show that mid-to-high 20s is common in southerly summer set-ups, but a small shift in cloud, sea-breeze influence or timing of sunshine can move the daily peak by a degree or two. That is why 26°C, 27°C and 28°C dominate the board rather than any extreme outcome, and why the market’s implied probability can look more concentrated than a sports line even when the forecast distribution is still fairly balanced. The broader weather backdrop has also been warmer than average this summer, with the Met Office saying daily maxima have been about 2.1°C above normal across the UK, which supports the market’s bias towards the upper-mid 20s rather than a cool-day outcome. [1][15]

Traders should watch the live forecast updates through the morning and early afternoon, because the settlement depends on the **highest temperature recorded at London City Airport Station** on the day, not a city-wide average, and small station-level changes can matter. The key catalyst is whether the expected high pressure and southerly flow hold long enough to deliver clear spells; if cloud thickens or winds back onshore earlier than expected, the most likely settlement can drift down a bucket. The contract also has a delayed finality element: revisions to readings within the market window are still possible until the first datapoint for the following day is published on the resolution source. [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

Polymarket-based markets settle through the UMA Optimistic Oracle on Polygon. A proposer submits the outcome, a two-hour challenge window opens, and unchallenged proposals finalise the resolution. Payouts settle automatically in USDC the moment the result is final — no bookmaker, no delay.

Kalshi-based markets settle in USD via the CFTC-regulated clearinghouse. Betfair Exchange settles in GBP/EUR net of commission. Manifold is play-money and does not pay out real funds.

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 Best Prediction Markets UK. 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.

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 Best Prediction Markets UK trigger KYC only above $1,500 of lifetime trading volume; under that you trade pseudonymously with a single wallet address.