Highest temperature in London on July 21?

Platform comparison

Market context

The market hinges on the peak Celsius reading at London City Airport (EGLC) on 21 July 2026, sourced directly from Wunderground’s daily history. With the settlement window closing at 12:00 UTC today, the 1% YES probability for the implied range suggests the crowd expects temperatures well below that threshold, likely reflecting typical midsummer averages for EGLC, which often hover between 18°C and 24°C.

Historically, EGLC rarely exceeds 28°C in July; the UK’s hottest July days typically occur further south or inland, such as at Heathrow or Cambridge. For instance, July 2022 saw London hit 40.3°C at Heathrow, but EGLC recorded only 34.1°C, illustrating the airport’s coastal moderation. This thermal buffer makes extreme highs improbable, aligning with the low crowd-implied odds and framing the 1% as a rational outlier bet rather than a mispriced opportunity.

Traders should monitor real-time feeds from the Met Office and Wunderground’s EGLC page as the day progresses, watching for any sudden heatwave announcements or shifts in the Atlantic jet stream. While no specific forecast has been issued for 21 July yet, the Met Office’s weekly outlook—updated daily—remains the primary dependency for temperature anomalies. A recent Met Office bulletin noted stable high-pressure systems over the UK through mid-July, reducing the likelihood of sudden spikes [1]. Programmatic approaches would automate polling of Wunderground’s API at 11:30 UTC to capture the day’s peak before settlement.

Sources: 1 · 2

Methodology

This page is a comparison snapshot: one live quote, four reference venues with their key attributes, and a single execution path — every trade button routes to Kalshi Fees, which mirrors the Polymarket order book directly.

Resolution & payout

Settlement runs on-chain. Polymarket's contract logic separates YES and NO shares as conditional tokens; at resolution the winning share lifts to $1.00 and the losing one to $0. The outcome input comes from the UMA Optimistic Oracle, which secures against bad resolution with a bond + dispute window.

Once finalised, the smart contract pays USDC to the holders' wallets within minutes — no withdrawal fees beyond Polygon network gas. Kalshi settles in USD via CFTC clearance, Betfair in account currency net of commission, Manifold in play-money mana with no cash-out.

FAQ

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.

What does Polymarket cost to trade?

Polymarket itself charges 0% — the only cost is the Polygon network fee, typically under $0.01 per transaction. Off-chain venues like Kalshi or Betfair charge 2-7% commission.

How fast are USDC deposits?

Polygon credits deposits after 12 confirmations — usually under 30 seconds. Withdrawals follow the same path and land back in your wallet within minutes.

Do I need to KYC for this market?

On Polymarket directly, no — it's wallet-based. Intermediary brokers like Kalshi Fees trigger KYC only above $1,500 of lifetime trading volume; under that you trade pseudonymously with a single wallet address.