Highest temperature in London on August 6?

Platform comparison

Market context

The relevant event is the highest temperature recorded at London City Airport on 6 August, which will be read from the daily history page once the first next-day data point is published, so programmatic traders usually treat the market as open until the source rolls over rather than until midnight local time.[2] Current crowd pricing of 0% for YES is best read as a stale or unmapped state, not as a meaningful forecast, especially because the listed outcomes are temperature buckets and the market only resolves when Wunderground posts the day’s final high.[2]

For context, London in August is usually mild rather than extreme, with monthly averages around the high teens Celsius, while published same-day forecasts for 6 August point to a high near 22°C and minimal rain.[1][4][13] That puts the market in a regime where the centre of mass is around low-20s buckets, but the upside tail still matters if a warm spell develops; recent UK weather reporting has already shown how quickly south-east England can swing into the mid-30s during summer heat events, including London reaching 26.6°C earlier in the 2026 season and Britain hitting 35°C in a separate heatwave.[10][15]

A practical trading setup is to watch forecast updates, model runs, and any late-shifting synoptic pattern that could alter the afternoon peak, then map those changes directly into the temperature intervals rather than a single-point guess.[4][15][16] For power users automating entries, the key dependency is the resolution source’s publication timing: once Wunderground posts the final history record for the station, the market can settle only against that observed maximum, so copy-trading and conditional orders should be keyed to the source refresh rather than to a generic weather app forecast.[2]

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 Kalshi 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.

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.

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.