Highest temperature in London on June 21?

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Market context

London’s hottest reading for the day is taken from London City Airport Station, so the relevant task is not to forecast the citywide average but the single maximum printed in the day’s Wunderground history entry. With the settlement window ending at 12:00 UTC, a programmatic approach would watch intraday observations and any late spike before the cutoff, rather than relying on evening conditions that arrive too late to matter. Current crowd pricing at **0% YES** is therefore a statement about the market’s scepticism, not about the final temperature path.

For context, London City Airport is in the city’s warm season by late June, with climate normals showing June sits inside the period when daily highs are generally above 67°F, but that still leaves a wide spread between ordinary warm days and genuinely hot outcomes.[2] The live observation feed at nearby London City Airport has recently shown only **13°C** with southerly wind and high humidity, which is far from a heat-event profile.[1] For traders using alerts, bots, or conditional orders, the historical analogue to watch is whether the midday maximum can break materially above the seasonal base case; if not, low-to-mid teens or low twenties Celsius remain more plausible than a standout high.

The main catalyst set is meteorological rather than event-driven: the Met Office forecast for London City Airport, current observations, and any short-term updates to the temperature curve will matter more than news flow.[4][1] In practice, a power-user would poll the station page or use a weather API proxy, trigger orders when the observed hourly trend crosses a chosen threshold, and then stop paying attention once the 12:00 UTC settlement boundary has passed. If a warm-air surge arrives early enough, it can still change the day’s recorded maximum, but late-afternoon heat cannot affect this market if it lands after the cutoff.

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). The odds column is filled only where we have clean data — that avoids the made-up numbers that get a network demoted when search engines cross-check against the source venue.

Resolution & payout

At resolution the UMA oracle takes over: a proposer posts the outcome with a bond, any token holder can dispute within two hours. Without dispute the result is accepted and the smart contract distributes USDC instantly.

On Kalshi (CFTC-regulated) resolution runs through their in-house clearing engine in USD. Betfair Exchange settles after match end in the account's local currency. Manifold pays no cash — only its in-platform "mana" currency.

FAQ

Where can I trade this market with the lowest fees?

On Polymarket App UK, 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.

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 it cost to trade on Polymarket App UK?

Zero. Polymarket App UK routes every order to the live Polymarket order book; the only cost is the Polygon network fee, typically under $0.01 per transaction.

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.