Highest temperature in London on June 27?

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Market context

The real-world event hinges on the highest temperature recorded at London City Airport on 27 June 2026, a date that falls squarely within the UK’s warm season, which typically runs from mid-June to early September with average daily highs exceeding 67°F (37]C). A power-user evaluating this market programmatically would first query historical Wunderground data for EGLC on 27 June across multiple years to establish a baseline distribution, then overlay current Met Office forecasts to refine the probability model.

Historically, late June in London has seen temperatures range from 18°C to 36°C, with the hottest June day ever recorded in London reaching 36.4°C at Heathrow, though London City Airport typically records slightly lower peaks due to its urban microclimate and proximity to the Thames [9]. The current crowd-implied probability of 0% for any outcome above the baseline suggests the market expects temperatures to remain within the seasonal average of 18–22°C, a view consistent with recent Met Office forecasts indicating a maximum of 31°C for the day, though this figure may reflect a “feels like” temperature rather than the actual air temperature [5].

Traders should monitor the Met Office’s hourly updates and any sudden shifts in southerly wind flow, which can bring warmer air from continental Europe, as well as real-time Wunderground data for EGLC to validate the market’s assumptions [2]. A recent report from the UK’s hottest June day ever, recorded on 24 June 2026 at 34.8°C, underscores the volatility of late-June temperatures and the need for dynamic, data-driven positioning [6]. Conditional orders tied to Wunderground’s live temperature feed would allow traders to hedge against unexpected heat spikes while maintaining exposure to the baseline expectation.

Sources: 1 · 2 · 3 · 4 · 5

Methodology

This page is a comparison snapshot: one live quote (Polymarket), four reference venues with their key attributes, and a single execution path — every trade button routes to PolyGram, 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

Where can I trade this market with the lowest fees?

On PolyGram, which mirrors the Polymarket order book at 0% fees. Kalshi charges up to 7% per trade; Betfair Exchange takes 2-5% commission on net winnings.

Is this market available outside the US?

PolyGram is available in most jurisdictions where Polymarket isn't directly accessible. Polymarket itself is geo-blocked in the US/UK/EU. Always check local regulations.

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 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.