Highest temperature in London on July 21?

Platform comparison

Market context

On 21 July 2026, the highest temperature recorded at London City Airport will determine which range this market resolves to. The 1% crowd probability currently assigned suggests traders expect a notably cool day for mid-summer in London, or that the market is pricing in genuine uncertainty about extreme heat thresholds. London City Airport's official weather station sits on the Thames, which can moderate temperature swings compared to inland locations, making it a conservative measurement point for heat events.

London's July temperature record stands at 40.3°C, set in 2022 during an exceptional heatwave. Since then, the UK has experienced variable summer patterns; July 2023 saw peaks around 32–35°C across the capital, whilst 2024 and 2025 produced more mixed conditions with several days below 25°C. Historical volatility in summer weather, combined with climate variability on annual timescales, explains why even mid-range temperature outcomes (28–32°C) carry meaningful probability mass. Traders comparing this market across platforms will notice Polymarket's decimal-odds format and Kalshi's binary structure handle temperature ranges differently; Betfair and Smarkets offer similar range-based settlement but with varying fee structures (typically 2–5% commission) that affect edge calculations on low-probability outcomes.

The Met Office publishes extended forecasts from mid-July onwards, and any early-summer heatwave warnings issued in June or early July would shift market expectations sharply. Atmospheric patterns driven by jet-stream positioning and high-pressure systems over the Atlantic become clearer only 10–14 days before the event, meaning material repricing should be expected as settlement approaches.

Methodology

We read Highest temperature in London on July 21? 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

Settlement is the biggest difference between the four platforms: Polymarket on-chain in USDC (instant), Kalshi USD via CFTC (T+1), Betfair and Smarkets in local currency via bank withdrawal (T+1 to T+3). On-chain settlement clears in minutes — the fastest payout path of the four.

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.

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.

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.

Which platform supports Klarna/SOFORT?

Directly: none. Polymarket accepts only USDC on Polygon. Polymarket Alternative offers a fiat on-ramp via Klarna or SOFORT (DE/AT/CH) and converts internally to USDC for the Polymarket order book. T+1 processing.