Highest temperature in London on August 19?

Platform comparison

Market context

On 19 August 2026, the highest temperature recorded at London City Airport will determine the settlement of this market. The resolution hinges on the Daily Observations table from Weather Underground rather than the Day High & Low summary section—a distinction that matters when intraday spikes occur. The current 0% implied probability across the crowd suggests either extreme confidence in a specific temperature band or sparse liquidity in this particular market segment.

Historical August temperatures in London rarely exceed 30°C, with the city's all-time August record standing at 36.4°C (set in 2022). The 19th falls mid-month, when summer heat typically peaks but before late-August cooling patterns emerge. Comparing across platforms reveals divergent approaches: Polymarket displays decimal odds and charges 2% on both sides, whilst Kalshi uses American odds with a 5% fee structure and stricter KYC requirements for US traders. Betfair and Smarkets, operating under UK gambling licences, offer tighter spreads on weather markets but impose different settlement protocols—Betfair references official Met Office data whilst Smarkets accepts Weather Underground feeds like this market does.

Traders should monitor the Met Office's seasonal forecasts released in July 2026 and any Atlantic weather systems that might push warm air into the UK during mid-August. The specificity of using City Airport observations (rather than broader London stations) creates a micro-location dependency; airport microclimates can differ by 1–2°C from central London. Early-August weather patterns will signal whether August 19 falls within a heat dome or cooler spell, directly influencing which temperature bands attract meaningful trading volume.

Methodology

This page compares Highest temperature in London on August 19? 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 Robinhood Prediction Markets, which mirrors the Polymarket order book at 0% fees.

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

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. Robinhood Prediction Markets 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. Robinhood Prediction Markets 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.