**Mild, settled high-pressure conditions over southern England are supporting overnight lows near 17–18°C for London on August 25, 2026, producing closely matched market-implied probabilities (17°C at 35.5%, 16°C at 28.5%, 18°C at 22.5%).** Official Met Office guidance highlights sunny intervals with a daytime maximum near 25°C and a minimum of 17–18°C, consistent with a stable airmass and light winds that limit both strong daytime heating and deep nocturnal cooling. Ensemble forecasts show minor spread around this range due to uncertainty in cloud cover and boundary-layer mixing overnight. Clear or partly cloudy skies promote radiative cooling after sunset, but the mild southerly or slack flow prevents temperatures from dropping much below the mid-teens, aligning with late-August climatology where urban heat-island effects in central London often keep readings 1–2°C above rural values. Recent model runs and the transition toward more unsettled Atlantic influence later in the week introduce the small downside risk reflected in the 16°C and 15°C probabilities. Traders are effectively pricing the narrow scientific uncertainty between official point forecasts and ensemble variability rather than any major regime shift.