Highest temperature in London on July 31?

Platform comparison

Market context

London has already been through another hot spell this summer, and the immediate read on the market is that the day is effectively in the books: the settlement cut-off is 12:00 UTC, while London’s late-afternoon warmth usually peaks later than that, so the relevant maximum has either already been set or will not count if it arrives after the window. The crowd-implied 0% YES reflects the fact that the contract is tied to a specific station reading at London City Airport rather than a citywide headline, so traders are really pricing the chance of a *very* high early-day maximum from a coastal-east London site.

The historical anchor is straightforward. London’s most extreme July heat has clustered around exceptional synoptic setups, with Heathrow reaching 37.8°C on 31 July 2020 and London stations touching 40.2°C on 19 July 2022; St James’s Park and Heathrow both reached that level in 2022, underscoring how rare top-end outcomes are even in a warming climate.[1][3][11][17] Against that backdrop, any YES outcome here would require a station-specific reading far above typical late-July London highs, which are usually in the low-to-mid 20s Celsius rather than the upper 30s.[6][7]

The main catalysts are the hourly observations from London City Airport and any short-lived convective or sea-breeze effects that could lift the midday maximum before the cut-off. National heatwave headlines matter less than the local station sequence, because the market resolves on the highest temperature recorded at EGLC on the day, not on a broader London average.[8] For traders, the key question is whether an early spike was already captured before midday UTC, since a late-afternoon surge would be irrelevant to settlement.

Sources: 1 · 2 · 3 · 4 · 5

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 Prediction Today. 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.

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.

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.