Highest temperature in London on August 8?

Platform comparison

Market context

London’s maximum temperature for 8 August is the key real-world event, and the contract’s own source rule matters more than generic city forecasts: settlement turns on the highest reading in Weather Underground’s Daily Observations for London City Airport, not the day-high summary. That makes the relevant cross-platform comparison fairly stark: Polymarket shows the contract already pinned at 28°C with 100% implied probability, while the available mainstream forecast material also points to a warm day, including AccuWeather’s 28°C high for London on 8 August and similar warm-day framing from other weather outlets.[1][2][4]

Historically, London August temperatures are volatile enough that a one-band miss is not unusual, but the market is effectively behaving like a clean, single-scenario contract rather than a live forecast. The key comparable is that recent London temperature markets have resolved tightly to the station record once the official reading was published, with no meaningful uncertainty after the datapoint landed.[17] Against that backdrop, the current 0% YES framing would be materially out of line with both the live market and analyst-style weather expectations; the spread is not between competing outcomes so much as between an obsolete view and the consensus that 28°C was the day’s maximum.[1][4]

For traders, the practical catalysts are procedural rather than meteorological: the first published datapoint for 9 August is the cut-off for any revisions, so the final Daily Observations entry is the decisive input.[1] In London, a UKHSA heat-health alert was in force from 8 August into 11 August, which supports the warm-day setup but does not itself determine the contract.[9] The main dependency is therefore whether Weather Underground’s station history for London City Airport matches the expected 28°C band once the day’s observation table is complete.[1]

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

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.

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.