Highest temperature in London on July 21?

Platform comparison

Market context

The market settles on the highest temperature recorded at London City Airport on 21 July 2026, with resolution sourced from Wunderground historical data. The 1% crowd probability reflects the specificity of hitting a particular temperature band on a single day in summer, where precision forecasting carries inherent uncertainty even with modern meteorological models.

London's July climate typically ranges between 18–25°C, with extremes rare but documented. The UK's highest July temperature on record stands at 36.5°C (Cheltenham, 2022), though London proper has not exceeded 34°C in July since 1976. Historical data from the Met Office shows that temperatures above 30°C occur in roughly 10–15% of July days in the capital, making higher-band outcomes materially unlikely but not implausible given climate variability and the 20-year forward timeframe to 2026.

Traders should monitor UK seasonal forecasts released by the Met Office and European weather models (ECMWF) as July 2026 approaches. Broader climate patterns—including Atlantic oscillations and North Atlantic sea-surface temperatures—influence summer heat waves in the UK. Recent years have seen increased volatility in European summer temperatures; the 2023 and 2024 seasons produced several record-breaking days across the continent. Settlement depends entirely on Wunderground's historical archive for London City Airport (EGLC), making data availability the critical dependency. The market window closes at 12:00 UTC on the settlement date, requiring traders to account for diurnal temperature cycles and potential data-reporting delays.

Methodology

This page reads Highest temperature in London on July 21? on-chain. Polymarket's quote comes directly from the Polygon order book — the only comparable venue with on-chain settlement. Kalshi (USD, off-chain), Betfair (GBP/EUR, off-chain) and Manifold (play-money) are listed alongside for venue context. Every CTA routes to BTC Prediction, which mirrors the Polymarket order book directly.

Resolution & payout

Settlement is on-chain via UMA Optimistic Oracle. A proposer posts the outcome with a bond, a two-hour dispute window opens, then the smart contract lifts winning conditional tokens to 1 USDC and sends payments to holders' wallets automatically. No withdrawal fees beyond Polygon gas.

Off-chain venues (Kalshi, Betfair, Smarkets) settle in local fiat through bank-side clearing — faster than SWIFT, slower than on-chain. Manifold pays no real cash.

FAQ

What are crypto prediction markets?

Crypto prediction markets are on-chain smart contracts where you buy YES or NO shares on a future crypto event (e.g. "BTC above $100k by year-end"). The market price between 0¢ and 100¢ is the implied probability.

Why USDC and not ETH or USDT?

USDC is the Polygon standard — audited reserves (Circle, monthly attestation), deepest order book, low gas costs. ETH volatility would distort probability quotes; USDT has thinner Polygon liquidity than USDC.

What does a transaction cost on Polygon?

Polygon gas is typically under $0.01 per transaction. A full trade cycle (Approve + Order + Fill) totals around $0.03 — compared to $5-50 on Ethereum mainnet.

Can I use Bitcoin directly?

No, Polymarket operates exclusively in USDC on Polygon. You can bridge BTC to USDC via an exchange or bridge service and deposit on Polygon — typically 10-30 minutes processing time.

Are crypto prediction markets taxable in the US?

In the US, prediction market gains are typically treated as ordinary income or short-term capital gains depending on holding period. Consult a tax professional for your specific situation — we cannot provide tax advice.