Highest temperature in London on June 30?

Platform comparison

Market context

The highest temperature recorded at London City Airport on 30 June 2026 will determine the outcome of this weather contract, with the market currently pricing the "YES" outcome at 0% probability. On Polymarket, this conditional token trades on the Polygon network using USDC, where the 0% price reflects a crowd consensus that the temperature will fall outside the specific range being bet on, likely due to the day's unsettled conditions.

Historical data frames this low probability against recent extremes; while London saw a record-breaking 37.8°C at Heathrow on 30 June 2024, the City Airport station typically records lower peaks due to its urban location and proximity to the Thames [9]. Conversely, the Met Office forecast for a similar early-June date in 2026 established a modest 17°C maximum under post-May unsettled conditions, suggesting that without a sustained heatwave, temperatures often remain well below the upper thresholds required for a "YES" resolution in this specific range [1].

Traders should monitor the Met Office red extreme heat warnings and the daily 10-day forecast for Newham, as these are the primary catalysts for temperature spikes [6]. The resolution depends entirely on the Wunderground data point published for the City Airport station, so any sudden shift in the southerly wind flow or humidity levels observed at 10:00 BST will be critical [2]. With the settlement window ending 12:00 UTC on 30 June 2026, the market will resolve once the first official data point for that date is published on the resolution source [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). That keeps the comparison honest — a single canonical probability across the row, with the venue-by-venue trade-offs spelt out in the columns next to it.

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?

Polymarket itself is geo-blocked in the US/UK/EU. Always check the legal status of prediction markets in your jurisdiction before trading.

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 does Polymarket cost to trade?

Polymarket itself charges 0% — the only cost is the Polygon network fee, typically under $0.01 per transaction. Off-chain venues like Kalshi or Betfair charge 2-7% commission.

Do I need to KYC for this market?

On Polymarket directly, no — it's wallet-based. Intermediary brokers like Polymarket Legit? trigger KYC only above $1,500 of lifetime trading volume; under that you trade pseudonymously with a single wallet address.

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.