Forecast models from the National Weather Service and private sources indicate a minimum temperature in San Francisco on September 18 most likely in the upper 50s Fahrenheit, aligning with the market's heaviest weighting on 58-59°F. Persistent marine layer influence and onshore westerly flow are expected to limit nocturnal cooling while preventing significant warming, consistent with mid-September climatology where average lows sit near 55.8°F. Recent model runs show the upper-level low departing to the northeast, allowing partial clearing but maintaining a stable marine boundary layer that caps overnight temperatures. No extreme events or strong offshore flow appear likely to push readings outside the 56-60°F band before resolution. Updated NWS guidance and next model cycles will provide the clearest near-term signals for any adjustments in trader positioning.