Highest temperature in London on July 20?

Platform comparison

Market context

London City Airport recorded its highest temperature on 20 July 2026, and the market now prices that outcome with certainty at the 25°C bracket. On Polymarket, the contract trades as a conditional token settled in USDC on Polygon, where the frontrunner outcome commands a 100% implied probability, leaving the “22°C or below” option at 0% [1]. This pricing reflects the on-chain mechanics locking in the resolution once the Wunderground data for EGLC is ingested, with settlement finalised by the 12:00 UTC deadline on 20 July 2026.

Historically, July in London averages 23°C, yet heatwaves regularly push temperatures above 30°C, with Heathrow hitting a record 40.2°C in July 2022 [4]. The current 0% probability for cooler outcomes aligns with this pattern, as Met Office data confirms that extreme heat is a recurring feature of midsummer in the capital [4]. Traders reading the 100% price on 25°C should note that while averages sit lower, recent years show volatility that frequently exceeds 30°C, making the 25°C bracket a statistically grounded consensus rather than an outlier.

Key catalysts for verification include the daily Wunderground history feed for EGLC, which serves as the official resolution source, and the Met Office’s seasonal summaries that contextualise July heat trends [4]. No new announcements are pending, as the event has already occurred; the focus now shifts to the automated ingestion of the temperature record. With the settlement window closed and the outcome confirmed on-chain, the market’s role is purely archival, reflecting the finalised data point rather than forecasting future volatility.

Sources: 1 · 2 · 3 · 4

Methodology

This page reviews Highest temperature in London on July 20? across five venues. The live probability is the Polymarket mid-price, sourced directly from the on-chain Polygon order book; the comparison columns benchmark each venue on fee structure, KYC, settlement currency and payment rails. Every CTA routes to PolyGram, which mirrors the Polymarket order book at 0% fees.

Resolution & payout

At resolution the UMA oracle takes over: a proposer posts the outcome with a bond, any token holder can dispute within two hours. Without dispute the result is accepted and the smart contract distributes USDC instantly.

On Kalshi (CFTC-regulated) resolution runs through their in-house clearing engine in USD. Betfair Exchange settles after match end in the account's local currency. Manifold pays no cash — only its in-platform "mana" currency.

FAQ

Where can I trade this market with the lowest fees?

Polymarket is geo-blocked in the US/UK/EU. The easiest 0%-fee broker into the same order book is PolyGram. Kalshi charges up to 7% per trade; Betfair Exchange takes 2-5% commission on net winnings.

Is this market available outside the US?

Polymarket itself is geo-blocked in the US/UK/EU. Always check the legal status of prediction markets in your jurisdiction before trading.

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.

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.