Highest temperature in London on July 21?

Platform comparison

Market context

London's weather on 21 July 2026 will determine which temperature band captures the day's peak reading at City Airport. The 1% crowd probability suggests traders expect a relatively cool day, with the implied consensus clustering around lower temperature thresholds rather than heat extremes.

July in London typically peaks between 20–24°C, though the month's range spans considerably wider. The UK's highest July temperature on record—32.0°C at Heathrow in 2022—remains an outlier; most summers see peak days in the mid-20s. City Airport, situated in East London near the Thames, runs slightly cooler than inland stations due to proximity to water. Historical data from comparable years shows that exceeding 28°C in mid-to-late July occurs in roughly one in five summers, making the crowd's low probability assessment consistent with baseline expectations rather than a forecast of unusual cold.

The Met Office's seasonal outlooks and Atlantic weather patterns will shape conditions through early July, with North Atlantic pressure systems and jet stream positioning the primary drivers of temperature variance by late month. Traders should monitor European heat dome developments in early July, as any ridge of high pressure persisting into the third week could shift outcomes materially. Current climate models, updated weekly, will provide the most actionable signals; significant model consensus shifts toward warmer scenarios would likely move the probability away from its current floor.

Methodology

This page reviews Highest temperature in London on July 21? 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 Prediction Today, 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

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.

Do I need to KYC for this market?

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

How reliable are the quoted odds?

The YES/NO percentages are the live mid-prices of the Polymarket order book. On deep markets they move every few seconds; on thinner ones you'll see short plateaus.