Highest temperature in Chicago on August 9?

Platform comparison

Market context

Chicago’s highest temperature on 9 August sits in a fairly narrow late-summer band, and the contract is being resolved off the hourly or daily observation record rather than a simple headline high/low display. Weather Underground’s Chicago history page shows a high of **85°F** and the surrounding August norms cluster around the low-80s, while long-run climatology for 9 August puts the average high at about **83.3°F** at Chicago and **83.2°F** in broader August records.[17][3][8] That makes the present **0% YES** crowd price look misaligned with the underlying seasonal baseline if the relevant outcome range is the low-to-mid 80s, although the market’s own distribution is concentrated much higher than that, with Polymarket showing **84–85°F at about 99.8%** and nearly all other buckets priced below 1%.[7]

Historical comparables support treating mid-80s as the modal outcome, not a tail case. AccuWeather’s recent Chicago history for 9 August shows an **87°F** high, while Weather Underground’s daily history for Chicago reports **85°F** on the same date; the National Weather Service’s climate page for O’Hare shows today’s maximum at **84°F** as of late morning and notes a much higher all-time maximum, which is useful mainly as a reminder that single-day spikes are possible but uncommon in this part of the calendar.[1][17][2] Against that backdrop, a 0% implied probability on the YES side appears to reflect contract-specific bucketing or platform pricing rather than a view that Chicago cannot reach the expected range on 9 August.[7]

For traders, the key catalyst is the final observational series from Weather Underground at Chicago O’Hare, because settlement depends on the highest reading in the **Daily Observations** table and revisions are only relevant until the first datapoint for the following date is published.[7] The practical dependencies are the day’s convective setup, cloud cover, and any storm timing: Chicago’s forecast and observed recent weather have shown humid, partly sunny conditions with thunderstorms in the region, which can cap daytime heating or briefly spike readings before outflow cools the site.[14][5] In cross-platform terms, the main comparison is between Polymarket’s near-certain pricing around **84–85°F**, the near-zero crowd view here, and the climatological expectation of an August high in the low 80s, with the discrepancy likely driven more by market structure than by a materially different weather read.[7][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 Kalshi vs Polymarket, 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

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'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.

Do I need to KYC for this market?

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

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.