Highest temperature in London on August 3?

Platform comparison

Market context

London’s hottest reading on 3 August will be measured at London City Airport Station, and the contract settles on the temperature band containing that daily peak rather than on an average or a noon snapshot. The market is currently pricing **0% YES**, which is unusually low for a summer temperature event and sits well below the sort of probabilities implied by mainstream weather-market pricing on similar London contracts, where traders usually cluster around the low-30s Celsius outcomes when a warm spell is in view.[4][11]

That current reading looks hard to reconcile with London’s late-summer climatology. Long-run August averages for London are far below heatwave territory, with typical daytime maxima around the low 20s Celsius, while the UK’s 2026 summer has already produced several notably warm days, including 26.6°C at Kew Gardens and a later 32.3°C reading elsewhere in London, showing that high-20s and low-30s outcomes remain plausible when the synoptic setup turns hot.[3][7][8] By contrast, the “0% YES” line suggests either an obvious mispricing or a market that is not yet reflecting the latest forecast consensus; on comparable London temperature events, market-implied probabilities and weather-model expectations have tended to move together rather than diverge sharply.[4][14]

For traders, the key catalysts are the Met Office and other forecast updates on the strength and timing of any warm plume, plus the actual Heathrow/London City Airport-style urban heat profile on the day, which can lift maxima above surrounding areas. The same market rules also matter: final resolution depends on the highest value recorded in the full observation window, and late revisions can still matter until the next day’s first datapoint is published on the source feed.[4] If forecast confidence increases for a clear, sunny afternoon with weak wind and dry air, the upper bands should tighten; if cloud, showers or a maritime breeze dominate, the lower bands become more defensible.

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 Best Prediction Markets. 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.

Do I need to KYC for this market?

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

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.