Highest temperature in London on August 11?

Platform comparison

Market context

On 11 August 2026, the highest temperature recorded at London City Airport will determine the settlement outcome for this market. The resolution hinges on the Daily Observations table from Weather Underground rather than the Day High & Low summary, a distinction that matters when intraday temperature spikes occur outside peak afternoon hours. London City Airport sits in East London's financial district, typically recording temperatures 1–2°C cooler than central London due to proximity to the Thames and surrounding water features.

August in London has seen peak temperatures range from 24°C to 40°C over recent decades. The Met Office's 30-year climate normals place the August average high at 23°C, though the 2022 heatwave pushed readings to 40.3°C at Heathrow. For context, markets on competing platforms—Kalshi, Betfair, and Smarkets—typically diverge on weather contracts around data-source precision and settlement timing. Polymarket's explicit reliance on Weather Underground's Daily Observations table removes ambiguity that sometimes arises on other books where multiple weather stations or summary methods create interpretation disputes. The current 0% implied probability suggests traders expect temperatures below the lowest range bracket available.

Traders should monitor the UK Met Office's extended forecast from mid-July onwards, as August weather patterns crystallise roughly two weeks before the event. Atlantic pressure systems and jet stream positioning determine whether high-pressure systems deliver continental warmth or Atlantic moisture. Recent summers have shown increasing volatility in peak-day temperatures, making historical August averages less predictive than real-time atmospheric indices tracked by meteorological services.

Methodology

This page compares Highest temperature in London on August 11? specifically across Polymarket, Kalshi, Betfair Exchange and Smarkets. The live probability is the Polymarket mid; the comparison columns summarise each venue's fee structure, KYC, settlement currency and payment rails. Every CTA routes to Polymarket Alternative, which mirrors the Polymarket order book at 0% fees.

Resolution & payout

Polymarket settles via UMA Optimistic Oracle on Polygon. A proposer posts the outcome with a bond, the two-hour window runs, then the smart contract pays USDC.

Kalshi settles USD through the CFTC-regulated clearinghouse — the cleanest variant, with heavier KYC. Betfair Exchange settles in account currency (GBP/EUR), net of 2-5% commission. Smarkets follows the same model as Betfair with a lower default 2% commission.

FAQ

What does Polymarket cost vs Kalshi?

Polymarket: 0% fees, only Polygon network costs (~$0.01/trade). Kalshi: up to 7% per trade plus spread. For high-frequency traders, Polymarket is dramatically cheaper.

Which platform has the deepest liquidity?

Polymarket — by a wide margin. Top markets reach $50-500M volume, Kalshi ~$200M cumulative, Betfair similar. Deeper liquidity means your trade moves the quote less.

Is Betfair a Polymarket alternative?

Only partially. Betfair Exchange is UK-focused with a sports-betting emphasis; they have politics markets but with thinner liquidity than Polymarket. Settlement in GBP/EUR, 2-5% commission on winnings.

Which platform is accessible globally?

Polymarket is geo-blocked in the US/UK/EU. Kalshi is US-only. Betfair and Smarkets are UK-restricted. Polymarket Alternative has a different geo footprint and routes to Polymarket's order book at 0% fees.

Are all these platforms regulated?

No. Kalshi is CFTC-regulated (US). Betfair and Smarkets are UK Gambling Commission licensed. Polymarket operates without explicit regulation — a different risk profile than a regulated sportsbook.