Highest temperature in London on August 4?

Platform comparison

Market context

The event is the highest daytime temperature recorded at London City Airport on 4 August, and the market is currently pricing a very strong chance of a mid-to-high 20s Celsius outcome rather than an extreme heat reading. Polymarket shows **28°C** as the clear frontrunner at **48%**, with **26°C**, **27°C** and **29°C** clustered much lower at **19%** each, which implies the crowd expects a warm but not exceptional London summer day.[3] That sits uneasily with the market’s **0% YES** crowd-implied probability in your prompt, so the main cross-platform read is that the listed contract price and the broader sentiment are not aligned.

Historical context points to why the contract is sitting in the upper 20s rather than the low 30s. London’s August climate norm is around the low 20s, and long-run August averages are far below the day’s hottest possible outcomes, so a 28°C print would already be meaningfully above average even if it is not rare in a warm spell.[11][13] Recent local heat signals have also kept traders alert: the Met Office said 26.6°C at Kew Gardens was London’s hottest day of 2026 so far, and UK heat alerts have already featured in recent coverage, which helps explain why the market has not anchored to a single-digit probability for 30°C-plus.[4][5][17]

The key catalysts are the short-range forecast updates, especially whether temperatures trend towards 27–29°C in the hours before the settlement window closes, and any shift in cloud cover, sea breeze or frontal timing that can cap the daily maximum at the airport station. AccuWeather’s monthly outlook currently shows London highs for early August running roughly from **67°F to 78°F** and specifically puts 4 August near **72°F**, which translates to the mid-20s Celsius and is consistent with a market centred around 26–28°C rather than the low 30s.[1] For traders comparing across venues, the practical gap is between the sportsbook-style weather view of a warm but ordinary day and the prediction market’s concentration in the high-20s band; at the moment, the contract is not pricing a broad heatwave, but a narrow temperature bin that would still be above seasonal average.[1][3]

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 Best Prediction Markets, 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

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.

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.