Highest temperature in London on June 21?

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Market context

London has just moved into a much warmer pattern, with the Met Office showing **28°C** for London City Airport on 21 June and the market’s current frontrunner clustered around **29°C**, with **30°C** also close behind. That leaves the crowd-implied 0% for the top end looking more like an artefact of stale pricing than a live read on conditions, especially with the settlement window already ending this evening. [8][1]

For context, this is a late-June London outcome that sits comfortably in the upper end of seasonal norms rather than in true outlier territory. The current spread of outcomes around 28–30°C suggests traders are reading the day as warm but not extreme, and that is consistent with the airport forecast rather than a sharp break to either much cooler or much hotter weather. A previous London City Airport weather history entry also shows a mid-60s Fahrenheit daytime reading in the same period, underscoring how quickly June maxima can swing from merely pleasant to notably warm. [1][7]

The main catalysts now are straightforward: the final airport observation, any late forecast adjustment from the Met Office, and whether cloud cover or seabreeze effects cap the peak before the noon settlement cutoff. The official London City Airport forecast is still the key live reference, and traders will be watching whether the daytime high holds near **28°C** or nudges higher into the **29–30°C** band before the market locks. [8][1]

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

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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.