Highest temperature in Paris on August 21?

Platform comparison

Market context

Paris is forecast to experience warm but not exceptional conditions on 21 August 2026, with meteorological models currently suggesting a high around 26–28°C at Le Bourget Airport. The 1% crowd probability reflects the specificity of the market's upper temperature bands, which likely begin at 30°C or higher. Over the past 48 hours, European weather models have shown slight cooling compared to earlier runs, with high-pressure systems expected to track northward rather than stall over the Île-de-France region, reducing the likelihood of the sustained heat needed to push temperatures into the 32–35°C range.

August temperatures at Paris-Le Bourget historically peak between 24–26°C on average, though the station has recorded readings above 30°C in roughly 5–10% of August days across the past two decades. The 2003 European heat wave and the 2022 summer heatwave both produced consecutive days exceeding 35°C in Paris, establishing that extreme August heat is meteorologically possible but requires specific atmospheric blocking patterns. Current ensemble forecasts do not indicate such a setup for late August 2026.

Traders should monitor the European medium-range forecast updates (ECMWF and GFS models) issued around 10–14 days prior to the settlement date, as these typically show whether any high-pressure anomalies develop. Tropical Atlantic activity and any late-summer heat dome formation across continental Europe would be the primary catalysts for material probability shifts. The resolution will depend on the precise Daily Observations table entry from Wunderground's Le Bourget station, not summary figures, making station-specific data accuracy critical.

Methodology

Methodologically we separate two layers: the live probability (Polymarket mid-price) and the platform attributes (fee, KYC, settlement currency, payment rails). That keeps the comparison honest — a single canonical probability across the row, with the venue-by-venue trade-offs spelt out in the columns next to it.

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

How does resolution work?

Through the UMA Optimistic Oracle on Polygon: a proposer submits the outcome, a two-hour challenge window opens, and USDC payouts settle automatically once the result is final.

What's the difference between YES and NO shares?

A YES share pays $1.00 if the event happens, $0 otherwise. A NO share pays $1.00 if the event doesn't happen. The market price between 0¢ and 100¢ is the implied probability.

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%.