Highest temperature in London on August 21?

Platform comparison

Market context

The Met Office records daily maximum temperatures across London's weather stations, with London City Airport serving as the official observation point for this market. On 21 August 2026, the highest temperature reading will determine which range the market resolves to, with resolution contingent on the Daily Observations table from Weather Underground rather than summary figures. The current crowd-implied probability of 0% suggests traders are pricing this as an extremely unlikely outcome for whichever temperature band is being tested, though the specific range threshold remains critical context for assessing whether this reflects genuine meteorological improbability or market mispricing.

August temperatures in London typically peak between 20–24°C, with historical data from the past decade showing that extreme heat days exceeding 30°C occur roughly once every two to three years during summer months. The 2022 heatwave saw London reach 40.3°C, an exceptional event that reframes baseline expectations; however, August 21 specifically has not produced notably anomalous readings in recent records. The 0% probability currently implied suggests the market is pricing against a particular temperature threshold—likely an unusually high band—rather than reflecting genuine certainty about typical August conditions.

Traders should monitor the Met Office's medium-range forecasts from mid-August onwards, as these typically gain reliability within the ten-day window. Atmospheric pressure patterns, jet stream positioning, and any high-pressure systems developing over continental Europe will be primary drivers of London's maximum temperature on that date. The UK's summer weather patterns remain subject to significant variability, making long-dated temperature markets inherently sensitive to forecast updates as the settlement date approaches.

Methodology

This page reviews Highest temperature in London on August 21? 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 Best Prediction Markets, 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 Best Prediction Markets. Kalshi charges up to 7% per trade; Betfair Exchange takes 2-5% commission on net winnings.

Is this market available outside the US?

Polymarket itself is geo-blocked in the US/UK/EU. Always check the legal status of prediction markets in your jurisdiction before trading.

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.