**Recent cooling after a mid-August heat spike has positioned London's overnight minimum temperature on August 21 near 12–14°C, with market-implied odds clustering tightly between 13°C (42.5%) and 14°C (37.5%).** Official Met Office guidance currently projects a daytime high of 21°C and overnight low of 12°C for the 21st, following 22°C/13°C on the 20th, as a fresher Atlantic air mass replaces warmer, more humid conditions. This shift reflects increased cloud cover and scattered showers that limit daytime heating while moderating radiative cooling overnight. Key differentiating factors include the degree of overnight clear spells (enhancing longwave heat loss), wind speeds (higher winds reduce boundary-layer cooling), and residual moisture from recent rain, which can raise dew points and suppress the minimum. Ensemble model consensus remains modest because small variations in timing of any showers or high-pressure building can swing the low by 1–2°C. Traders are therefore weighting the balance between continued gradual cooling and the chance of slightly milder nights if skies stay more overcast, consistent with typical late-summer variability in the UK. Updated Met Office and ECMWF runs over the next 48 hours will provide the next high-resolution guidance ahead of the observation window.