Highest temperature in London on June 28?

Platform comparison

Market context

The real-world event in question is the highest temperature recorded at London City Airport on 28 June 2026, a date that has just passed with current observations showing a maximum of 31.1°C yesterday and forecasts for 26°C today. This market currently sits at 0% implied probability for any YES outcome, suggesting the crowd believes the temperature will fall outside the specified resolution range, despite recent heatwave activity.

Historical precedents frame this probability sharply: London experienced its hottest June day ever in 2022, with temperatures soaring to 36.4°C at the city and 40.2°C at Heathrow, while a record-breaking June day in May 2026 hit 34.8°C across the UK[5][9]. Yesterday’s 31.1°C reading at London City Airport, a significant +9.2°C anomaly, indicates that extreme heat is not merely theoretical but actively occurring in the region, making the 0% crowd-implied probability a notable divergence from analyst consensus on heatwave persistence[10].

Traders should monitor the Met Office’s 7-day forecast for London City Airport, which currently predicts 26°C with sunny intervals, alongside real-time Wunderground data that will serve as the official settlement source[1][2]. The key catalyst is the confirmation of whether today’s temperature will exceed the threshold, dependent on the southerly wind flow and falling pressure observed in current conditions, which have historically driven temperature spikes in the capital[2]. Any announcement of extended heatwave warnings or shifts in the jet stream could alter the final settlement, as the settlement window closes at 12:00 UTC on 28 June 2026.

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

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 vs Polymarket. 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.

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.

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.