Highest temperature in London on July 20?

Platform comparison

Market context

The market tracks the peak temperature recorded at London City Airport on 20 July 2026, with settlement tied to Wunderground’s daily history for station EGLC. Today’s live reading shows 13°C at the same location, but the resolution window has already closed, explaining the crowd-implied 0% probability for any active outcome.

Historically, mid-July highs in London typically range between 22°C and 30°C, with extreme outliers like the 40.2°C recorded in 2022 at Heathrow. However, London City Airport, situated closer to the Thames and surrounded by urban cooling effects, rarely exceeds 32°C. The current 0% probability suggests the market has already resolved, likely to a lower range such as 18–20°C, consistent with recent cool, humid conditions and falling pressure noted in BBC Weather data.

Traders approaching this programmatically would script a daily fetch from Wunderground’s EGLC history endpoint, parsing the “max temp” field at 00:00 UTC post-event. Key dependencies include the exact timestamp of Wunderground’s data update and any station recalibrations. With the settlement window ending 2026-07-20T12:00:00Z and today being 21 July, no new catalysts exist; the outcome is fixed, and any automated strategy must now focus on archival verification rather than live forecasting.

Sources: 1 · 2

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

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 Kalshi Fees. Kalshi charges up to 7% per trade; Betfair Exchange takes 2-5% commission on net winnings.

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 Kalshi Fees 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.