Highest temperature in London on August 9?

Platform comparison

Market context

London’s key reference point is the highest **observed** temperature at London City Airport, not the headline “day high” shown elsewhere on Weather Underground, so a programme that polls the Daily Observations table is the right way to resolve the market. On the current setup, the key task is simply to map the final Celsius reading into the market’s bins and ignore any later revision unless it appears before the first datapoint for the following date, which the contract treats as the cut-off.

For context, London has a long tail of late-summer heat spikes, but the August record is still far above ordinary seasonal conditions. The UK’s hottest August day remains 38.5°C at Faversham in 2003, while London has reached 36.4°C at Heathrow and Kew Gardens in early August 2020, and 40.2°C at Heathrow and St James’s Park in July 2022.[13][14][11] By contrast, long-run August averages for London are much lower, so the pricing of any threshold above the low 30s usually depends on a genuine heatwave rather than a normal warm spell.[12][4]

For traders running scripts or conditional orders, the practical watchlist is the live station feed and any late-day updates to the Wunderground history page, especially if the maximum is recorded near the market’s settlement window. Recent reporting on the UK’s 2026 summer heat noted renewed high pressure across southern and central Britain on 8–9 August, with regional highs around 31–32°C in London and the South East, which is the sort of setup that can push a market from one Celsius bucket into the next.[10][19] In programme terms, the relevant dependency is not the forecast screenshot but the final station observation sequence, because a single late peak can decide the entire outcome.

Sources: 1 · 2 · 3 · 4 · 5

Methodology

This page reviews Highest temperature in London on August 9? 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 Kalshi Fees, 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 Kalshi Fees. 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.

Do I need to KYC for this market?

On Polymarket directly, no — it's wallet-based. Intermediary brokers like Kalshi Fees 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.