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 Polymarket contract, which currently prices the "YES" outcome at 0% probability. On-chain, this conditional token sits on the Polygon network, settled in USDC, where traders are betting that the day’s peak will fall outside the narrow range implied by the market’s zero-valuation stance.

Historically, late June in London often sees highs near 20°C, but recent years have delivered extreme outliers. In 2022, the UK recorded a record-breaking June day with 37.3°C in London, and in 2023, temperatures soared to 36.7°C in Somerset during an intense heatwave that disrupted transport and broke multiple records[8][9]. These precedents suggest that a 0% probability assignment may be overly conservative, as the climate has shifted toward more volatile summer peaks.

Traders should monitor the Met Office’s daily forecast updates and any sudden shifts in southerly wind flow, which can drive rapid temperature increases. The National Weather Service has already noted rising pressure and falling humidity at London City Airport, conditions that often precede heat spikes[3]. Additionally, the BBC Weather forecast for today lists a high of 23°C, with sunny intervals and a gentle breeze, indicating that the day may not reach the extremes seen in past heatwaves[2]. Any official announcement of a heat alert from the Met Office would be a critical catalyst to reassess the current pricing.

Sources: 1 · 2 · 3 · 4 · 5

Methodology

This page is a comparison snapshot: one live quote, four reference venues with their key attributes, and a single execution path — every trade button routes to PolyGram, 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?

Polymarket is geo-blocked in the US/UK/EU. The easiest 0%-fee broker into the same order book is PolyGram. 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'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.

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.

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.