**Forecast models and National Weather Service guidance indicate the overnight low for Austin on September 18 will likely fall in the low-to-mid 70s under mostly clear to partly cloudy skies with light southeast winds of 5 mph or less.** High dew points near 70°F and modest radiative cooling overnight limit further drops, while the absence of a strong frontal passage or significant cloud cover keeps temperatures from deviating sharply. Minor differences among model runs—particularly in exact wind speeds, humidity advection, and any residual high clouds—create the tight spread across the 70–77°F bins, with traders weighting the latest NWS point forecasts (around 73–76°F) against ensemble spreads. No major weather systems are expected to alter the pattern before resolution.