Highest temperature in London on June 21?

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Market context

London’s highest temperature for 21 June will be set by the reading at London City Airport Station, and the market is effectively pricing how warm the city gets by the afternoon peak. The current crowd-implied probability of **0% YES** looks detached from the broader late-June set-up: Polymarket’s own live page says official observations and climatological baselines place late-June London highs near **22°C**, while the market leader there is **29°C** at **32%** and **30°C** at **30%**, which implies traders are leaning hard towards a hot outlier rather than a mild day.[1]

That is materially different from the usual historical framing, because late June in London is often warm but not routinely extreme, and the answer depends on whether the day clears the upper 20s at the airport station rather than the more typical low-20s band.[1][5] Cross-platform pricing also appears to diverge: a Bitget predictions page shows volume concentrated around higher temperature ranges, including a prominent **22°C or below** bucket and a separate **26°C** line, suggesting a broader market still leaves room for a much cooler outcome than Polymarket’s front-runner implies.[3] By contrast, the Met Office’s London City Airport forecast at one point pointed to a **28°C** maximum, which would be supportive of the hotter bins if it holds into settlement.[7]

For traders, the main catalyst is the short-range forecast evolution for London City Airport rather than any scheduled announcement, because the contract resolves on the highest observed temperature on the day, not a closing print or a citywide average.[6][9] The key dependency is whether the airport station records a brief spike in the late afternoon; even small shifts in cloud, wind, or convective heating can move the winner between adjacent bins. With settlement already effectively at hand, the practical watchlist is the final Met Office and BBC Weather updates against the live observations feeding the airport station, since those are the inputs most likely to explain any late repricing.[4][7]

Sources: 1 · 2 · 3 · 4 · 5

Methodology

This page reviews Highest temperature in London on June 21? across five venues. We show live odds for Polymarket-based markets (sourced from the Polygon order book); for other venues we list platform attributes, since the comparable contracts are not exposed via a public API on every venue. Every CTA points at Best Prediction Markets — the application we operate, where you trade directly against the Polymarket order book at 0% fees.

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 Best Prediction Markets, 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?

Best Prediction Markets 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.

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 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.