Highest temperature in Seattle on August 5?

Platform comparison

Market context

Polymarket is pricing the Seattle heat-up contract at **0% YES**, which leaves the on-chain market on Polygon implying no credible expectation of a reading in the positive buckets, even though settlement is still tied to the final Sea-Tac Airport high reported by Weather Underground. The contract pays out in USDC through conditional tokens, so the only thing that matters is the maximum temperature recorded at Seattle-Tacoma International Airport on 5 August, not the daytime forecast alone.

For context, Seattle’s August highs are usually in the upper 70s to low 80s Fahrenheit, but recent history shows that Sea-Tac can still push into the mid-80s during warmer spells. WeatherSpark shows a 24-hour high of 84.0°F at KSEA on 1 August 2026, and the same market family on Polymarket for 4 August had the leading band at 84–85°F, which suggests traders have recently treated the low-to-mid 80s as the most relevant comparison range rather than extreme-heat outcomes.[2][13]

A trader watching this market would focus on the post-event Weather Underground history page for KSEA, since the contract settles only after the final daily values are complete and the next day’s first observation is published.[3] The main catalysts are short-term forecast revisions, any heat advisory or air-mass change affecting Puget Sound, and the timing of the airport’s observations; local outlets had already been flagging recent heat-advisory conditions in the Seattle area, which can matter if they are carried forward into the exact settlement day.[5][15]

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

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.

UK Frequently Asked Questions

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.

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%.