Highest temperature in San Francisco on July 13?

Platform comparison

Market context

San Francisco International Airport faces a rare heat spike on 13 July 2026, with the market pricing a specific high-temperature threshold at just 6% probability. Historical July data shows daily highs typically hover around 70°F, rarely exceeding 79°F, making any significant deviation an outlier event [1]. The last time KSFO recorded 87°F was during a 2013 Bay Area heat wave, tying a record set that year, while the all-time city maximum of 106°F occurred in September 2017, not mid-July [2][5]. Given that July 13, 1972, saw 116°F in Healdsburg but only moderate temps in the city itself, the 6% implied probability reflects the statistical improbability of a triple-digit or near-record day at the airport during this specific window [3].

Traders should monitor the National Weather Service’s 48-hour forecast for KSFO, which will confirm if a marine layer failure or inland heat dome is approaching the coast. Recent heat wave coverage notes that San Francisco Airport temperatures can spike rapidly when Pacific winds weaken, though such events are infrequent in mid-July [2]. No major weather announcements have been issued yet for the 13th, but the settlement depends entirely on the Wunderground daily record for KSFO, meaning even a brief 10-minute spike above the threshold resolves the contract [9]. With the settlement window closing at 12:00 UTC on 13 July, the market effectively bets on whether the marine buffer will hold against a potential inland pressure shift.

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.

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 Best Prediction Markets. 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.

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.

How reliable are the quoted odds?

The YES/NO percentages are the live mid-prices of the Polymarket order book. On deep markets they move every few seconds; on thinner ones you'll see short plateaus.