Highest temperature in Seattle on August 5?

Platform comparison

Market context

Polymarket is effectively pricing **no meaningful upside** in this Seattle temperature contract today, with the market showing **0% YES** despite the event still being resolved against the final Weather Underground reading for Seattle-Tacoma International Airport (KSEA). On-chain, traders express that view in USDC on Polygon via conditional tokens, so the spread between the eventual daily high and the listed bracket matters more than the headline forecast before settlement.

That near-zero price is easiest to read against Seattle’s August climate profile and nearby market history. Seattle’s normal August highs are in the low 70s Fahrenheit, but recent late-summer days have still produced mid-to-upper 70s and occasional low-80s readings, which is enough to keep bracket markets sensitive to a single warm afternoon rather than the monthly average.[1][6] Comparable Polymarket temperature contracts for Seattle have traded with sizeable probability mass in the high-80s brackets when the market sees heat risk, showing that this venue can reprice quickly if forecast guidance shifts toward a warmer ridge pattern.[2][15]

The main catalysts are the short-range forecast updates, especially any change in the marine layer, offshore flow, or inland heat spread ahead of the closing observation at KSEA. Traders should watch the National Weather Service forecast cycle and any local heat headlines, because those are the inputs most likely to move the implied distribution before Weather Underground finalises the day’s high.[7][18] Since settlement depends on the airport station’s completed daily history, the practical risk is not abstract “Seattle weather” but whether the station prints a late-afternoon spike large enough to move the final bracket.[2]

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

Polymarket-based markets settle through the UMA Optimistic Oracle on Polygon. A proposer submits the outcome, a two-hour challenge window opens, and unchallenged proposals finalise the resolution. Payouts settle automatically in USDC the moment the result is final — no bookmaker, no delay.

Kalshi-based markets settle in USD via the CFTC-regulated clearinghouse. Betfair Exchange settles in GBP/EUR net of commission. Manifold is play-money and does not pay out real funds.

UK Frequently Asked Questions

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.

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%.