Highest temperature in London on July 31?

Platform comparison

Market context

The key event is the highest temperature recorded at London City Airport on 31 July, measured in Celsius and then mapped into the market’s fixed outcome bands. For a programmatic trader, the clean way to approach it is to ingest the Wunderground history page, watch the day’s maximum print rather than the hourly path, and compare that value to the band boundaries before the settlement window closes.

London’s late-July extremes show why the current 0% implied chance can still be read as a live weather distribution rather than a dead market. The Met Office records Heathrow at 37.8°C on 31 July 2020, and London has also seen 40.2°C at Heathrow and St James’s Park in July 2022, so the city is capable of exceptional spikes even in a settled summer pattern.[3][11][14] Against that backdrop, recent hot July trading around the low-to-mid 30s Celsius underlines how quickly the terminal band can shift if a heat plume builds over the southeast.[2][17]

What matters now is whether the day’s maximum at London City Airport was already set before the deadline and whether any late-afternoon or early-evening heating could still change the final print. A bot or copy-trading workflow should therefore monitor the airport station’s observed maximum, not London-wide headlines, and should treat nearby stations such as Heathrow and central London as context only; they help with regime detection, but they do not determine settlement.[3][15] If the market remains open close to the cutoff, the most useful signals are updated station observations and any Met Office or BBC coverage of a regional hot spell, because those can explain whether the airport’s final maximum is likely to finish above or below the quoted range.[4][17]

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

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 Bot UK 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.