Highest temperature in London on June 21?

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Active sub-markets

Market context

London’s temperature on 21 June will be set by the day’s *single highest reading* at London City Airport Station, using Wunderground’s hourly data and whole-degree Celsius buckets. The crowd-implied 0% YES looks less like a view on the weather itself than a reaction to the market’s settlement mechanics: the outcome is pinned to one station, one calendar day, and a temperature range rather than an exact figure, so traders are effectively pricing a narrow slice of the day’s heat profile rather than “London” in the broader sense.[2][10]

The closest historical guide is early-summer London climatology rather than headline heat-wave language. London City Airport’s warm season runs from mid-June into early September, with June sitting inside the period when highs can move quickly with sun, cloud cover and sea-breeze effects.[6] Current forecasts for the airport show temperatures around 27–30°C at the start of the week, which is consistent with the idea that a late-June heat ridge can push the day’s peak into the upper 20s or low 30s, but the exact settlement band will depend on the maximum observed at the station, not the forecast high.[7][8]

For traders, the main catalyst is the live forecast path into the settlement window: Met Office updates, short-term model shifts, and any heat advisories are more relevant than distant outlooks.[7] In the latest coverage, London City Airport sits under an Amber Warning for Extreme Heat on AccuWeather’s forecast page, which reinforces that the market is leaning on whether the warmth persists through the afternoon rather than on any formal event or announcement.[3] The key dependency is the Wunderground history page publication after the day ends, because the market cannot settle until the relevant data point has been posted.[2]

Sources: 1 · 2 · 3 · 4 · 5

Methodology

This page tracks Highest temperature in London on June 21? across four political prediction venues. Live odds come from the Polymarket order book (the deepest political prediction-market book). Kalshi is the CFTC-regulated US alternative, Betfair the established UK sports-exchange with politics markets, Manifold the open play-money variant. Election Predictions UK routes every trade through to Polymarket — at 0% fees.

Resolution & payout

For political markets the resolution source is decisive. Polymarket defines a concrete source per contract (e.g. AP, Reuters, official electoral commission) and uses the UMA Optimistic Oracle as the on-chain dispute mechanism. With a clearly defined outcome the USDC payout lands within minutes of the final confirmation.

FAQ

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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.

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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.