Highest temperature in San Francisco on August 10?

Platform comparison

Market context

Polymarket is pricing the contract at **0% YES**, so the market is effectively saying San Francisco International Airport will not post a highest temperature in the resolved range on 10 August 2026, with settlement in USDC via Polygon conditional tokens. The market resolves off the **highest reading in Weather Underground’s Daily Observations table**, not the headline day high/low summary, so traders need to watch the intraday table rather than the summary panel for the final print.[12]

That 0% sits against a city that usually stays mild in August, with normal highs around the low 70s Fahrenheit and recent observed peaks in the upper 60s to low 70s at SFO on 10 August 2026 before the market window closed.[6][12] San Francisco’s broader August record is still materially higher — the airport’s climate normal page shows a record maximum of 87°F for 10 August — but such values are rare in the marine layer regime that dominates the coast.[6][14] In practice, markets like this often hinge on whether a short-lived downslope or offshore flow breaks through the usual fog-and-breeze pattern.

For traders, the main catalyst is the live observation feed itself: the Weather Underground Daily Observations table at KSFO, plus any late-day warming, cloud breakup, or wind shift that could lift the station’s top reading before the close of the settlement window.[12] The National Weather Service’s current conditions for San Francisco show the airport area still under a cool, humid marine influence, which usually caps upside unless conditions change quickly.[13] If nearby forecasts and airport observations remain stuck near the mid-to-upper 60s, the 0% price is consistent; if an afternoon spike appears in the station log, the contract can reprice abruptly on-chain.

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.

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%.