Highest temperature in London on June 23?

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Market context

The Met Office forecasts a daily high of 33°C for London City Airport on 23 June 2026, with conditions expected to remain warm and muggy under clear skies[4][8]. This real-world baseline frames the current Polymarket pricing, where the crowd-implied probability sits at 100% for a "YES" outcome, yet the frontrunner outcome is actually "33°C" at 56% probability, suggesting traders are betting on a specific range rather than a binary certainty[1]. The on-chain mechanics utilise USDC on the Polygon network, where conditional tokens allow precise exposure to temperature bands, with $70.1K in volume already distributed across outcomes from 32°C or below to 37°C[2].

Historical context reveals that 26.6°C was recorded at Kew Gardens recently, marking the hottest day of 2026 so far, yet June typically sees significantly higher peaks in London[7]. Forecasts for this specific date point toward peak temperatures of 34–38°C across the city, indicating that the current 33°C Met Office figure may be a conservative estimate compared to seasonal trends[1]. The market assigns a 32% probability to outcomes of 32°C or below, reflecting uncertainty about whether the forecast will hold or if a heat spike will push temperatures higher[1].

Traders should monitor the Met Office daily updates and Wunderground data releases, as the resolution source requires the first data point for 24 June to be published before the market can resolve[1][2]. Any announcements regarding heatwave advisories or changes in atmospheric pressure, currently falling at 1012mb, could act as catalysts for temperature shifts[4]. The dependency on Wunderground's official record means that traders must watch for real-time updates on the resolution page, as revisions to temperatures are only considered until the first datapoint for the following date is published[2].

Sources: 1 · 2 · 3 · 4 · 5

Methodology

This page is a comparison snapshot: one live quote (Polymarket), four reference venues with their key attributes, and a single execution path — every trade button routes to Kalshi UK, which mirrors the Polymarket order book directly.

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 Kalshi 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 does it cost to trade on Kalshi UK?

Zero. Kalshi 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.

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.