Highest temperature in Chicago on July 27?

Platform comparison

Market context

Chicago's summer temperatures on 27 July will be recorded at O'Hare International Airport, the official National Weather Service station for the metropolitan area. The settlement mechanism uses Wunderground's historical data feed, which aggregates hourly readings throughout the day to determine the single highest temperature. Polymarket currently prices this contract at 0% implied probability across all temperature bands, suggesting either incomplete market formation or that traders are awaiting clearer seasonal forecasts before committing USDC collateral to conditional tokens on this specific date.

Historical July temperatures at O'Hare cluster between 78°F and 88°F for daily highs, with extreme heat events pushing into the low 90s roughly once per decade. The record high for any July day stands at 97°F (set in 1934), though more recent decades show a pattern of peaks in the 85–90°F range. Comparable dates from previous years—late July typically marks the tail end of Chicago's warmest period—provide anchoring points for evaluating which temperature band the market should price most heavily.

The National Weather Service issues extended forecasts six to ten days before 27 July 2026, with meaningful updates arriving in the five days prior to settlement. Traders should monitor whether a high-pressure system establishes itself over the Midwest during that window, as such patterns drive sustained heat. The settlement window closes at 12:00 UTC on 27 July, giving traders until mid-morning Chicago time to adjust positions based on early-day temperature readings and intraday forecasts.

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

Settlement runs on-chain. Polymarket's contract logic separates YES and NO shares as conditional tokens; at resolution the winning share lifts to $1.00 and the losing one to $0. The outcome input comes from the UMA Optimistic Oracle, which secures against bad resolution with a bond + dispute window.

Once finalised, the smart contract pays USDC to the holders' wallets within minutes — no withdrawal fees beyond Polygon network gas. Kalshi settles in USD via CFTC clearance, Betfair in account currency net of commission, Manifold in play-money mana with no cash-out.

FAQ

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.

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 UK trigger KYC only above $1,500 of lifetime trading volume; under that you trade pseudonymously with a single wallet address.