Highest temperature in London on July 23?

Platform comparison

Market context

Polymarket is pricing the London City Airport reading for 23 July at **0% for YES**, so the contract is effectively saying the market assigns no chance that the day’s highest recorded temperature lands in the specified YES range. The settlement is tied to Wunderground’s finalised daily data for London City Airport, with resolution based on the highest temperature recorded that day and measured to whole degrees Fahrenheit for settlement purposes, even though the user-facing framing is in Celsius.[1]

For a late-July London temperature market, the useful comparison is not a single headline forecast but the typical spread between morning conditions, daytime warming, and any cloud, wind or rainfall that can cap the high. On Polymarket, that means the live price is a pure expression of where traders think the final airport observation will settle once the day’s data is complete, with USDC collateral on Polygon and the outcome represented through conditional tokens rather than a conventional cash bet. A 0% quote usually reflects either a very narrow strike structure or a market that has already been priced as practically out of reach before the final reading is published.[1]

The main catalysts for traders are the hourly forecast updates around London, any shift in cloud cover or rain timing, and the final Wunderground post for EGLC once the day is closed out. Because resolution waits for finalised data, intraday spikes matter only if they are captured in the station’s recorded maximum, not merely in local forecasts.[1]

Sources: 1

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

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

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.

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.

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.