Highest temperature in London on August 13?

Platform comparison

Market context

On 13 August 2026, the highest temperature recorded at London City Airport will fall into one of several defined ranges. The market resolves using the Daily Observations table from Weather Underground rather than the Day High & Low summary—a distinction that matters when automated data feeds or manual transcription introduce variance. For programmatic traders, this means building a resolver that queries the specific endpoint and validates against the primary source before settlement, as secondary summaries occasionally lag or round differently.

London's August temperatures have historically clustered between 20–28°C, with extremes rare but documented. The 2022 heatwave pushed readings above 40°C across parts of southern England, though London City Airport itself recorded 37.8°C that August. Comparable August days in 2019 and 2023 saw highs in the 24–26°C range. The 0% crowd probability suggests traders are pricing in either a genuinely cool forecast for that specific date or uncertainty about whether the market will settle at all—a reasonable hedge given dependency on a single weather station's data integrity.

Traders should monitor the UK Met Office's extended outlook from mid-July onwards; any Atlantic low-pressure systems or heat dome formations would shift the distribution materially. Historical data availability from Weather Underground's archive is reliable, but confirming the station's operational status before settlement window close (12:00 UTC on 13 August) prevents disputes. Conditional orders tied to Met Office alerts or automated threshold triggers would reduce manual monitoring overhead for those running systematic weather portfolios.

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 Fees. 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.

Do I need to KYC for this market?

On Polymarket directly, no — it's wallet-based. Intermediary brokers like Kalshi Fees trigger KYC only above $1,500 of lifetime trading volume; under that you trade pseudonymously with a single wallet address.