Highest temperature in London on June 28?

Platform comparison

Market context

The real-world event hinges on the peak temperature recorded at London City Airport on 28 June 2026, a date falling squarely within the UK’s warm season when daily highs typically exceed 19°C. Historical data shows London’s average daily high in late June sits around 22–24°C, with the city’s all-time record of 40.2°C set in July 2022 at Heathrow and St James’s Park[10]. Current market pricing assigns a 43% probability to 26°C as the frontrunner, with 25°C at 24%, suggesting traders expect a notably warm but not extreme day[1]. The crowd-implied 0% YES probability for the lowest range likely reflects a mismatch in the user’s query or a misread of the distribution, as even the lowest plausible outcomes (17–19°C) carry measurable odds[2].

A programmatic trader would monitor real-time feeds from Wunderground and the Met Office, cross-referencing with BBC Weather’s hour-by-hour updates for sudden shifts in cloud cover or wind direction[3][4]. The key catalyst is the UK’s forecasted heatwave, with ITV News reporting temperatures up to 40°C expected across the country on 24 June 2026, indicating sustained high-pressure conditions that could elevate June 28’s peak[8]. Dependencies include the resolution source’s data publication time, which must occur before 12:00 UTC on 28 June, and the accuracy of the station’s sensor calibration, as minor errors could skew the final range[2]. Traders should also track southerly wind patterns and humidity levels, which currently sit at 88%, as these factors amplify daytime heating[4].

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.

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?

On Polymarket directly, no — it's wallet-based. Intermediary brokers like Kalshi Fees 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.