Highest temperature in London on July 23?

Platform comparison

Market context

Polymarket is pricing London’s 23 July temperature at the London City Airport station with the **26°C** bucket leading on **47%**, while **27°C** is next at **32%**.[2] Because settlement is based on the highest observed temperature on the day in Celsius, holders of USDC on Polygon are really trading the probability that the station’s daily peak lands in the warmer mid-to-high 20s rather than the more ordinary low-20s summer band.

That pricing is above the broad July norm for London, where typical highs are often around **23°C** and the month also brings intermittent rain and breezier conditions.[1] Recent London summer coverage has emphasised how quickly mid-July heat can build and then ease, with late-20s readings common in hotter spells and official heat alerts already used in the city this month.[3] In practice, a 0% YES crowd price implies the market is treating the current day’s peak as highly likely to fall inside one of the listed temperature ranges rather than outside them.

The main catalysts are the morning forecast updates, any shift in cloud cover or rainfall timing, and whether warmer air aloft translates into a brief afternoon spike before the Wunderground reading window closes at the settlement cutoff.[1] Traders usually watch the Met Office and local station forecasts most closely, because a small change of 1–2°C can move the result from one contract bucket to the next, which matters directly for the conditional tokens backing the market.

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

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.

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 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.

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.