Current National Weather Service forecasts and ensemble model runs indicate a high-pressure ridge over the eastern Pacific will advect warmer, drier air into the Bay Area on May 18, supporting afternoon highs at or above 68 °F with high confidence. Typical May climatology for San Francisco shows average daily maxima near 67 °F, and the latest guidance places the most probable range in the upper 60s to low 70s under mostly sunny skies and light onshore flow. Traders have priced this outcome at 95 percent because multiple deterministic and probabilistic runs from the Global Forecast System and European Centre for Medium-Range Weather Forecasts converge on temperatures meeting or exceeding the threshold. A sudden strengthening of the marine layer or an earlier return of stratus could cap readings in the mid-60s, but such a shift would require rapid changes in boundary-layer moisture not currently signaled by observations or model soundings.