Highest temperature in San Francisco on August 13?

Platform comparison

Market context

San Francisco's weather on 13 August 2026 will depend heavily on the strength of the marine layer and any heat dome positioning across the western United States during mid-August. The current 0% crowd probability suggests traders expect temperatures to fall outside whatever range this market specifies, though the settlement window closes at midday local time, potentially capturing only partial daily heating.

Historical August temperatures at San Francisco International Airport rarely exceed 85°F, with the station's all-time August high standing at 103°F in 2000 during an exceptional heat event. Most years see peak August readings between 75–82°F, constrained by the Pacific's cooling influence and the bay's geography. The 0% probability implies the market's temperature brackets may be positioned at extremes—either unusually high thresholds that require sustained heat dome conditions, or conversely, ranges that exclude typical summer patterns entirely.

Traders should monitor National Weather Service forecasts for the western ridge pattern in early August 2026, particularly whether high-pressure systems develop inland or remain offshore. The marine layer's persistence through morning hours typically caps daytime highs, though offshore winds can briefly elevate temperatures. Any significant atmospheric setup changes in the week preceding 13 August would alter the probability calculus materially. Weather Underground's Daily Observations table, specified as the resolution source, records readings at fifteen-minute intervals, so the final settlement depends on actual station data rather than forecast models.

Methodology

We track Highest temperature in San Francisco on August 13? across the five venues with material prediction-market liquidity. The probability shown is the live Polymarket mid; the comparison rows summarise how each venue treats the underlying contract — fees, KYC thresholds, settlement currency, deposit options. The highlighted row marks the cheapest route into Polymarket's order book.

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

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 Prediction Today. Kalshi charges up to 7% per trade; Betfair Exchange takes 2-5% commission on net winnings.

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%.