Highest temperature in San Francisco on June 30?

Platform comparison

Market context

The real-world event centres on the peak temperature recorded at San Francisco International Airport on 30 June 2026, a date historically marked by mild coastal conditions rather than extreme heat. Current crowd-implied probability for any temperature above the lowest range sits at 0%, reflecting a market consensus that a heatwave is virtually impossible on this specific day.

Historical data frames this low probability with strong precedent: June in San Francisco typically sees average highs near 70°F, rarely exceeding 75°F, with the highest daily average high occurring on 29 June[1]. While the Bay Area has recorded extreme outliers, such as 103°F on 13 June 2000 and 106°F in September 2017, these events are anomalies tied to rare inland heat domes, not standard June weather patterns[5][6]. Recent 15-day data ending 29 June 2026 shows a peak of just 72.6°F, reinforcing the view that conditions remain within normal seasonal bounds[2].

Traders should monitor the development of high-pressure systems over the Great Basin, which can occasionally drive hot air toward the coast, though no such system is forecast for 30 June. The primary dependency is the absence of a marine layer break, which would otherwise allow inland heat to penetrate the airport station. Recent reporting on Bay Area heat records confirms that while extreme weeks occur, they are infrequent and usually clustered in July or August rather than late June[9]. With no significant weather announcements suggesting an imminent heat dome, the divergence between sportsbook lines (which would likely offer no odds on such an event) and the 0% prediction-market probability aligns with analyst consensus on the contract’s low risk.

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.

FAQ

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

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.

How fast are USDC deposits?

Polygon credits deposits after 12 confirmations — usually under 30 seconds. Withdrawals follow the same path and land back in your wallet within minutes.