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 this market's outcome. The resolution hinges on Weather Underground's Daily Observations table rather than its Day High & Low summary—a distinction that matters when automated feeds diverge or sensors record conflicting peaks. London City Airport sits in the Docklands, where urban heat effects and proximity to the Thames create microclimatic conditions distinct from central London or Heathrow observations. Traders must verify which station Wunderground designates as the official source before settlement, as platform specifications occasionally shift between weather stations mid-contract.

August temperatures in London typically range between 18–24°C, with extremes rare but documented; the city recorded 40.3°C in July 2022 during an exceptional heatwave. Historical data from 2015–2024 shows August 11 specifically averaging around 20–21°C, with only two instances exceeding 26°C in that decade. The current 0% implied probability suggests traders view extreme heat as implausible for that particular date, though seasonal forecasting remains inherently uncertain two years ahead.

Kalshi, Polymarket, and Betfair structure this market differently: Kalshi typically offers binary or narrow-range contracts with fixed fees; Polymarket uses decimal odds and AMM pricing; Betfair and Smarkets employ traditional order books with commission on winnings. Each platform's liquidity and settlement precision vary. Traders comparing books should note that Wunderground's API occasionally experiences delays in updating Daily Observations, potentially affecting resolution timing across platforms with different settlement protocols.

Methodology

We read Highest temperature in London on August 11? from four platform perspectives: Polymarket (on-chain CLOB), Kalshi (CFTC-regulated exchange), Betfair Exchange (sports book exchange), Smarkets (peer-to-peer betting exchange). Polymarket's live mid is the canonical probability; the side-by-side columns benchmark fees, KYC, settlement currency and deposit rails so you can choose the venue that fits your jurisdiction and trade size.

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

Polymarket vs Kalshi — which is better?

Depends on your location. Kalshi is CFTC-regulated, US-only with full KYC. Polymarket is global, on-chain, no KYC up to $1,500. Polymarket has ~10x higher liquidity but higher regulatory risk.

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.

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.

What about Smarkets as an alternative?

Smarkets is a UK betting exchange with a lower default commission (2%) than Betfair. Liquidity on political markets is below Polymarket, comparable to Kalshi. Geo-blocked in many jurisdictions.

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.