Highest temperature in London on July 9?

Platform comparison

Market context

London City Airport is currently experiencing a sharp heat spike, with temperatures hitting 32°C (89°F) by midday and forecast highs for July 2026 ranging up to 33°C (92°F), directly challenging the market's 0% probability for extreme heat outcomes[1][3]. This sudden surge in the last 24 hours marks a clear departure from the typical July average of 22–24°C, driven by an ongoing warm spell that has pushed conditions well beyond historical norms[5].

Historical data from comparable warm spells in London shows that July highs rarely breach 30°C, yet recent anomalies have consistently pushed temperatures into the 31–33°C range, making the current 0% crowd-implied probability appear statistically misaligned with the observed trend[1][9]. The market's frontrunner outcome of 34°C at 50% probability reflects this growing consensus that the warm spell will intensify rather than dissipate, suggesting the current pricing may be underestimating the likelihood of record-breaking highs[5].

Traders should monitor the Met Office's updated maximum daytime forecast of 28°C for today, which may be revised upward if the current high-pressure system persists through the settlement window[4]. Key catalysts include the scheduled release of the Met Office's 7-day outlook and any announcements regarding the continuation of the warm spell, as these will directly influence the final temperature reading at London City Airport[4]. The settlement window ending 2026-07-09T12:00:00Z means the next 12 hours of weather data will be decisive for the market resolution[5].

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

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 Prediction Today. Kalshi charges up to 7% per trade; Betfair Exchange takes 2-5% commission on net winnings.

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.

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.