Highest temperature in London on June 21?

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Market context

Polymarket has this London City Airport temperature contract priced at **0% YES** just after the June 21 observation window, even though the market was only resolving to the *highest* recorded station temperature for that day on USDC collateralised, Polygon-based conditional tokens.[1] That makes the current price look less like a live weather forecast and more like a settlement check: traders are effectively waiting for the Wunderground daily history page to publish the final datapoint that locks in the day’s maximum in Celsius.[1][2]

Late-June London usually sits in the low 20s Celsius, so outcomes near the high 20s and low 30s are the part of the curve that matter when reading this book.[1][5] Polymarket’s own contract page had the front-runners as **29°C** at 41% and **30°C** at 34%, which implies the market had already moved far above climatological normal before settlement risk took over.[1] For a hands-on trader, the relevant comparison is not the city average but the day’s realised maximum at EGLC, since the contract resolves on the single highest station reading rather than a daily mean or forecast high.[1][2]

The main catalyst is the release timing and finalisation of the Wunderground history data: the market cannot resolve until the first datapoint for the following day is published, and revisions before that cut-off still count.[1][2] In practical terms, that means the key watch item is whether any late evening or overnight observation on the source page shifts the recorded peak before the dataset rolls forward. AccuWeather had London City Airport under an **Amber Warning for Extreme Heat** with a forecast around 82°F/61°F on June 21, which is consistent with elevated upside risk for the recorded maximum, even if the market has already pushed that uncertainty into the final settlement phase.[7]

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

Is this market available outside the US?

Kalshi UK 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.

Do I need to KYC for this market?

Not under $1,500 of lifetime trading volume. Above that threshold, Kalshi UK triggers a quick verification flow that finishes in 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.