Recent Met Office guidance for London on 18 August points to a cloudy overnight period with only isolated light rain, limiting radiative cooling and supporting minimum temperatures of 16–17 °C at standard observing sites. This follows a brief spell of higher pressure that kept the region mild after earlier heat, with forecast model consensus showing little change in the 24–48 hours before the daily minimum is recorded. London’s urban heat island effect further elevates overnight lows relative to rural stations, while light winds and increased cloud cover reduce the chance of sharper drops. These conditions explain why traders have concentrated implied probability on 18–19 °C outcomes, viewing 17 °C or lower as unlikely absent clear-sky radiational cooling that current guidance does not support. Updated model runs and official minimum readings expected later today will determine final resolution.