Trader consensus on Polymarket prices a 57% implied probability for San Francisco's highest temperature reaching 68°F or higher on April 18, driven by the latest National Weather Service forecasts showing a building upper-level ridge over the West Coast that promotes sunnier conditions and limits persistent marine layer stratus. Recent observations through April 15-16 reveal highs climbing into the mid-60s amid northwest winds aiding fog burn-off, a shift from cooler, cloudier early-month patterns with scattered rain. Ensemble model guidance supports mid-to-upper 60s peaks at SFO, the market's resolution station, though lingering coastal cool air could cap readings below 68°F if stratus reforms overnight. Updated 12Z model runs on April 17 will provide the next key refinement.