Highest temperature in London on August 12?

Platform comparison

Market context

On 12 August 2026, the highest temperature recorded at London City Airport will fall into one of several defined ranges. The market resolves using the Daily Observations table from Weather Underground rather than the Day High & Low summary—a distinction that matters when automated feeds pull data at different intervals or when station recalibration occurs mid-day. For programmatic traders, this means validating the exact URL endpoint and timestamp logic before deploying conditional orders; Weather Underground's API documentation specifies observation granularity, but discrepancies between summary and raw tables have historically caused settlement disputes on similar markets.

August temperatures in London typically peak between 20–25°C, with extremes above 30°C occurring roughly once per decade. The 2022 heatwave saw 40.3°C recorded in nearby areas, though London City Airport itself recorded 37.8°C that month. The current 0% crowd probability suggests either extreme confidence in a narrow range or insufficient liquidity to establish a baseline. Historical volatility in August weather—driven by Atlantic low-pressure systems or continental high-pressure ridges—means the crowd's implied distribution may be underweighting tail outcomes.

Traders should monitor the Met Office's extended forecast from late July 2026 onwards, particularly any shift towards blocking patterns or tropical air mass advection. The UK's seasonal weather briefings, typically published fortnightly, will signal whether August 2026 tracks towards the cooler 1990s baseline or warmer 2010s trend. For those building automated resolution checkers, note that Weather Underground occasionally flags data as provisional for 48 hours post-observation; settlement may require manual verification against the station's primary archive if discrepancies emerge.

Methodology

We track Highest temperature in London on August 12? 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.

UK Frequently Asked Questions

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 Polymarket Review UK. 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.

Is Polymarket legal in the UK?

Polymarket is accessible to UK traders but is not UKGC-licensed. It operates under US CFTC jurisdiction. UK residents face no domestic legal prohibition on using it, but UKGC consumer protections do not apply. For UKGC-regulated alternatives, Betfair Exchange and Smarkets offer similar prediction-style markets.

Do I pay tax on prediction market profits in the UK?

UKGC-licensed platform profits (Betfair, Smarkets) are typically tax-free gambling winnings for UK individuals. Polymarket profits involve USDC crypto transactions, which HMRC treats as Capital Gains Tax events. Keep full transaction records and report via Self Assessment if gains exceed £3,000 per tax year.

How do I deposit on Polymarket from the UK?

UK traders typically fund Polymarket via Coinbase UK, Kraken or Revolut — buying USDC with GBP and transferring to a Polygon-compatible wallet (MetaMask, Coinbase Wallet). Polymarket's onboarding walks you through the bridging process. Typical GBP-to-USDC conversion costs 0.5–1%.