Highest temperature in London on August 3?

Platform comparison

Market context

The event is the highest temperature measured at London City Airport on 3 August 2026, and a **YES** share pays out if the reading falls inside the specified temperature band when the market settles. In prediction-market terms, the price is the crowd’s live estimate of that outcome: a 0% YES price means traders currently see that band as essentially impossible, not that the weather is locked in.

For context, early-August London temperatures usually sit well below the upper 20s or 30s, but they can jump sharply during short hot spells. Recent market commentary points to London forecasts clustering around 31–32°C under sunny conditions, with the main trading interest centred on 30°C and 31°C rather than extreme heat, and wider UK coverage has already shown 2026 producing several notably hot days, including readings above 35°C elsewhere in England[2][11][15]. That is why a very low implied probability can be read as a view that the airport station will not hit the market’s target band, rather than a broad statement about whether London will be warm.

Traders should watch the latest forecast updates, because this market is driven by the actual maximum recorded at a single station, not by the general London weather narrative. The key dependencies are the day’s cloud cover, any inland hot-air surge from the continent, and whether temperatures peak before the settlement window closes at 12:00 UTC; if conditions turn more stable and sunny, the odds of a higher reading rise quickly, while a marine breeze or earlier cloud tends to cap the upside[2][14]. The resolution source is Wunderground’s history page for London City Airport, so late adjustments in the station record matter more than citywide averages[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

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 Prediction Market 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 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.

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.