Highest temperature in London on July 31?

Platform comparison

Market context

London City Airport’s maximum on 31 July will be set by the warmest reading recorded there before the market’s 12:00 UTC settlement window closes, so the practical question is whether the day’s peak arrives early enough to count. For a programme trading this market, the useful input is not the forecast headline alone but the intraday temperature path: if the warmest hour lands after noon UTC, it is irrelevant to settlement even if the afternoon becomes hotter later.

The current 0% yes price is easy to read against London’s July history. The Met Office notes that Heathrow reached 37.8°C on 31 July 2020, while London has also seen 40.2°C at Heathrow and St James’s Park during the July 2022 heatwave, showing that very high outcomes are possible in exceptional synoptic setups.[3][10][15] Even a more ordinary warm July day can still produce highs in the low-to-mid 30s Celsius in central London, so a flat zero implies the market is pricing either a strict range mismatch or a belief that the relevant band is effectively out of reach.[2][13]

A trader watching this programmatically would focus on Met Office short-range guidance, Heathrow/London area observations, and the timing of any heat pulse from continental air advection, then map those temperatures into the market’s Celsius bands before noon UTC. The main catalysts are the morning model updates, cloud cover, wind direction, and whether temperatures peak early or continue rising through the afternoon; any live weather dashboard that can be polled at fine intervals is more useful here than a static daily forecast.

Sources: 1 · 2 · 3 · 4 · 5

Methodology

This page reviews Highest temperature in London on July 31? 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 Polymarket Review UK, 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 Polymarket Review UK. 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 Polymarket Review UK trigger KYC only above $1,500 of lifetime trading volume; under that you trade pseudonymously with a single wallet address.