Highest temperature in London on August 4?

Platform comparison

Market context

The day’s **highest temperature in London** will be set by the warmest reading at London City Airport, and the market is currently pricing a modestly warm outcome rather than a true heat spike. On Polymarket, the leading bucket is **28°C at 48%**, with **26°C and 27°C at 19% each** and **29°C also at 19%**; by contrast, this contract’s crowd-implied probability is marked at **0% YES**, so there is a clear divergence between venue pricing and the current benchmark on this specific market. Monthly forecast data for London still point to ordinary August warmth, with forecast highs around **22–23°C** on nearby dates and a broader August range of roughly **67°F to 78°F** in one city forecast, which supports a centre-of-mass outcome in the low-to-mid 20s Celsius rather than extreme heat.[2][3][9][10]

Historical context suggests traders should treat this as a distribution around the upper 20s only if a hot continental feed develops. London’s summer climatology is usually much cooler than the hottest possible buckets here, and recent UK heat episodes have shown that London can briefly surge into the high 20s or low 30s when a heatwave aligns with clear skies and southerly flow; BBC reporting this summer also noted a **35°C** forecast during a broader UK heatwave, underlining that elevated tails remain possible when national patterns turn hot.[15][17][18] The most important catalysts are the final morning-to-midday temperature trajectory at London City Airport, any late-arriving cloud or rain band, and whether the UK heat pattern strengthens or fades over the next few hours; unless a fresh hot spell is locked in, traders usually see the highest probability mass cluster around the **26°C–29°C** band rather than the extreme buckets.[16]

Sources: 1 · 2 · 3 · 4 · 5

Methodology

This page reviews Highest temperature in London on August 4? across five venues. The live probability is the Polymarket mid-price, sourced directly from the on-chain Polygon order book; the comparison columns benchmark each venue on fee structure, KYC, settlement currency and payment rails. Every CTA routes to Kalshi vs Polymarket, which mirrors the Polymarket order book at 0% fees.

Resolution & payout

Polymarket-based markets settle through the UMA Optimistic Oracle on Polygon. A proposer submits the outcome, a two-hour challenge window opens, and unchallenged proposals finalise the resolution. Payouts settle automatically in USDC the moment the result is final — no bookmaker, no delay.

Kalshi-based markets settle in USD via the CFTC-regulated clearinghouse. Betfair Exchange settles in GBP/EUR net of commission. Manifold is play-money and does not pay out real funds.

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 Kalshi vs Polymarket. 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 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.