Highest temperature in London on July 31?

Platform comparison

Market context

The temperature at London City Airport on 31 July is the reference point, and the market is effectively asking where the day’s peak will land rather than whether it will be warm at all. The current crowd-implied probability of 0% for **YES** looks detached from recent London summer behaviour: the long-run July average daily high is around the low-to-mid 20s °C, but London regularly prints well above that in hot spells, and the city’s all-time July peak is 37.8°C at Heathrow on 31 July 2020. [11][3][4]

That history matters because this contract resolves on a single station reading, so small shifts in local conditions can move the outcome between adjacent temperature bands. Polymarket’s displayed favourite is the **73-74°F** bucket at 100%, while the contract specification on Wunderground ties settlement to London City Airport rather than citywide averages, which is the key distinction for cross-platform comparison; sportsbook-style weather lines, where available, typically track forecast maxima rather than the final observed station reading, so they can diverge from prediction-market prices when traders anchor to one hot or cool scenario. [12][2]

For traders, the main catalysts are the afternoon forecast trend, any official updates from the Met Office, and whether cloud, sea-breeze influence, or convective shower risk caps the airport maximum before the 12:00 UTC settlement window closes. Recent UK coverage has described late-July conditions as capable of pushing London into the low 30s Celsius, with some forecasts placing the capital near 32°C, which is materially above the market’s 0% YES posture and suggests the contract is being priced as a relatively narrow outcome despite the warm-season backdrop. [10][15]

Sources: 1 · 2 · 3 · 4 · 5

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 vs Polymarket, which mirrors the Polymarket order book directly.

Resolution & payout

Polymarket-based markets settle through the UMA Optimistic Oracle on Polygon. A proposer submits the outcome, a two-hour challenge window opens, and unchallenged proposals finalise the resolution. Payouts settle automatically in USDC the moment the result is final — no bookmaker, no delay.

Kalshi-based markets settle in USD via the CFTC-regulated clearinghouse. Betfair Exchange settles in GBP/EUR net of commission. Manifold is play-money and does not pay out real funds.

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.

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 vs Polymarket 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.