Trader consensus on Polymarket assigns a 53.5% implied probability to a high of 78°F or higher at San Francisco International Airport on April 4, driven by the persistence of a record-breaking March heat wave that saw downtown highs reach 90°F—the city's warmest March on record—under a stubborn upper-level ridge suppressing marine stratus. National Weather Service guidance and ensemble model runs from GFS and ECMWF project continued above-normal temperatures in the mid-to-upper 70s, with offshore flow potential limiting coastal cooling, far exceeding April climatological averages of 64–66°F where highs rarely top 76°F. Uncertainties include possible marine layer redevelopment overnight; watch NWS updates for refined 00Z model runs resolving the market.