Recent National Weather Service forecasts for San Francisco International Airport project a daytime high of 66°F or warmer on May 19 amid weakening onshore flow and reduced marine layer influence, driving the 80% implied probability for that outcome. Persistent Pacific advection typically caps May highs near the 67°F climatological average, yet current model runs show warmer air masses and partial stratus erosion allowing greater afternoon warming. Breezy westerly winds at 10–20 mph may enhance mixing and briefly elevate readings, while any late-day fog return could trim peaks into the mid-60s. Traders watch for updated model guidance and real-time observations through evening resolution, as small shifts in boundary-layer conditions determine whether the high exceeds the key threshold.