Recent Met Office guidance and short-range ensemble models indicate a minimum temperature near 18–19 °C for London on 17 August, with the market’s tight clustering around these outcomes reflecting genuine forecast uncertainty just 48 hours out. Overnight radiative cooling will depend on the timing and extent of any incoming cloud or light rain, which can limit temperature drops by several degrees, while clearer spells and lighter winds allow more efficient heat loss to space. Subtle differences in steering flow and boundary-layer mixing also separate the 17 °C and 20 °C tails. Updated model runs and the evening forecast briefing will provide the clearest signal before the night begins.