Highest temperature in London on July 31?

Platform comparison

Market context

London’s top temperature is the day’s *high watermark* risk, and the crowd’s 0% YES implies the market is treating an extreme reading as effectively impossible. On the Wunderground London City Airport series, that leaves the favourite firmly in the lower summer bands rather than anything that would challenge the hotter outcomes; the consensus is therefore a mild-to-warm finish, with the contrarian value, if any, sitting in the more modest upper-middle ranges rather than the tail ends. Historically, London can spike hard when a heat plume reaches south-east England: Heathrow hit 37.8°C on 31 July 2020, the UK’s third hottest day on record, and Kew Gardens reached 37.3°C the same day.[3][6] More broadly, London’s July climate is usually much cooler than that, so a forecast distribution anchored around the low-to-mid 20s Celsius is the sensible handicapper’s baseline rather than anything near the 2020 outlier.[7][15]

For traders, the key catalysts are the Met Office forecast trend, the strength and placement of any late-summer high-pressure ridge, and whether dry continental air or cloud cover dominates the afternoon peak. The settlement cut-off is noon UTC, but the market resolves on the day’s highest temperature at London City Airport, so the afternoon rise still matters only until that window closes on the Wunderground record. Recent UK weather coverage has shown how quickly London can swing from comfortable July conditions to 30C-plus heat when a heatwave locks in, with BBC reporting temperatures in the upper 20s to mid-30s across England and Wales during a recent spell.[17] That keeps the upside tail live in principle, but the current 0% YES pricing leaves the value debate centred on whether the market is underestimating a routine warm-day outcome rather than a true heatwave breakout.

Sources: 1 · 2 · 3 · 4 · 5

Methodology

We track Highest temperature in London on July 31? across the five venues with material prediction-market liquidity. The probability shown is the live Polymarket mid; the comparison rows summarise how each venue treats the underlying contract — fees, KYC thresholds, settlement currency, deposit options. The highlighted row marks the cheapest route into Polymarket's order book.

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 Who Will Win. 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 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.