Highest temperature in Chicago on August 9?

Platform comparison

Market context

Chicago’s peak temperature on 9 August will be set by the highest reading in Weather Underground’s **Daily Observations** for the Chicago O’Hare station, not the headline “Day High & Low” summary. That matters for tooling: a programmatic monitor should watch the station history feed for the first observation dated 10 August UTC, because that is the point at which the prior day’s record is effectively closed for settlement.

The current 0% implied probability looks out of step with recent Chicago August norms, where the National Weather Service places the 9 August average high at about **83.3°F** and record highs can reach the upper 90s, with 100°F+ only an exceptional event.[5][10] Comparable Chicago August readings also cluster in the mid-80s; AccuWeather’s recent history and forecast pages show highs around **84–87°F** for 8–10 August, which is consistent with the market’s likely temperature bins rather than an extreme-heat outcome.[1][6]

For a trader using bots or conditional orders, the practical catalysts are the same ones that move the final observation: updated forecasts, storm timing, cloud cover, and any cooling from lake breeze or rainfall. Weather Underground’s history page and the underlying hourly observations are the key data sources to poll; once the first 10 August observation appears, late revisions are no longer relevant for this contract.[17][18] If you are automating, the safest approach is to key off the station-level observation timestamp, not the daily summary or a third-party forecast panel, because those can diverge materially during the day.[14][18]

Sources: 1 · 2 · 3 · 4 · 5

Methodology

This page reviews Highest temperature in Chicago on August 9? 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 Polymarket Review UK, which mirrors the Polymarket order book at 0% fees.

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.

UK Frequently Asked Questions

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 Polymarket Review UK. 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.

Is Polymarket legal in the UK?

Polymarket is accessible to UK traders but is not UKGC-licensed. It operates under US CFTC jurisdiction. UK residents face no domestic legal prohibition on using it, but UKGC consumer protections do not apply. For UKGC-regulated alternatives, Betfair Exchange and Smarkets offer similar prediction-style markets.

Do I pay tax on prediction market profits in the UK?

UKGC-licensed platform profits (Betfair, Smarkets) are typically tax-free gambling winnings for UK individuals. Polymarket profits involve USDC crypto transactions, which HMRC treats as Capital Gains Tax events. Keep full transaction records and report via Self Assessment if gains exceed £3,000 per tax year.

How do I deposit on Polymarket from the UK?

UK traders typically fund Polymarket via Coinbase UK, Kraken or Revolut — buying USDC with GBP and transferring to a Polygon-compatible wallet (MetaMask, Coinbase Wallet). Polymarket's onboarding walks you through the bridging process. Typical GBP-to-USDC conversion costs 0.5–1%.