Highest temperature in London on August 21?

Platform comparison

Market context

The UK Met Office will record the highest temperature at London City Airport on 21 August 2026, with settlement determined by the Daily Observations table on Weather Underground rather than summary figures. The current crowd-implied probability of 0% suggests traders are pricing this as an unlikely outcome, though the specific temperature threshold triggering a YES resolution remains unspecified in available market documentation.

August temperatures in London have historically ranged between 15°C and 28°C, with the airport station recording a 30-year average high of approximately 22°C. The city's record August temperature stands at 36.4°C, set in 2022, though such extremes occur roughly once per decade. Seasonal patterns show late August typically cooler than mid-month peaks, which may explain the market's bearish positioning relative to more volatile summer dates.

Traders should monitor the Met Office's medium-range forecasts from mid-August 2026 onwards, as atmospheric patterns driving heat waves typically become predictable five to ten days in advance. The UK's summer weather remains sensitive to Atlantic pressure systems and North African heat transport; any blocking high-pressure system establishing over continental Europe in late August would be the primary catalyst for elevated temperatures. Cross-platform comparison shows prediction markets currently offer no meaningful divergence on this contract, with Kalshi and Polymarket both reflecting minimal trading activity and consensus scepticism about extreme heat materialising on this specific date.

Methodology

This page reviews Highest temperature in London on August 21? across five venues. The live probability is the Polymarket mid-price, sourced directly from the on-chain Polygon order book; the comparison columns benchmark each venue on fee structure, KYC, settlement currency and payment rails. Every CTA routes to PolyGram, which mirrors the Polymarket order book at 0% fees.

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 PolyGram. Kalshi charges up to 7% per trade; Betfair Exchange takes 2-5% commission on net winnings.

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.

Do I need to KYC for this market?

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