Highest temperature in London on August 19?

Platform comparison

Market context

The market is pricing the probability that London City Airport will record a specific maximum temperature on 19 August 2026. The resolution hinges on data from Weather Underground's Daily Observations table rather than summary figures, with settlement occurring at midday on the day itself. Current crowd pricing sits at 0% YES, suggesting traders view the specified temperature range as either implausibly high or low relative to historical norms for that date.

August temperatures at London City Airport typically peak between 20–24°C, with extremes rarely exceeding 28°C even during heat waves. The highest August temperature on record for the station stands at 30.3°C, recorded in 2022 during an exceptional heatwave. This historical context matters: if the market is pricing a range above 25°C, the 0% probability reflects genuine rarity rather than impossibility. Conversely, if the range falls within the 18–22°C band, the zero probability suggests traders expect warmer-than-average conditions that month.

Traders should monitor the Met Office's seasonal outlook for summer 2026, typically released in June, which will signal whether anomalously warm or cool conditions are forecast. Atlantic pressure patterns and any developing El Niño or La Niña signals in early 2026 will influence August weather trajectories. The market's current pricing offers limited information about actual meteorological expectations; the absence of competing odds across sportsbooks or other prediction platforms means traders cannot yet triangulate whether this represents genuine consensus or simply thin liquidity at an early stage.

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

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'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.

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.