Mild atmospheric conditions overnight have anchored trader consensus around an 11°C low for London on September 21, with market-implied odds at 100% for that outcome versus just 0.1% for 8°C or below. Official Met Office guidance and station data indicate minimum temperatures near 9–13°C under partly clear skies and light southerly flow, consistent with late-September climatology where radiational cooling is moderated by residual warmth and weak pressure gradients. No significant cold-air advection or stronger high-pressure setup materialized to drive deeper nocturnal drops. While forecast models carry small uncertainty ranges from localized microclimates or measurement timing, a plunge below 8°C would require atypical clear-sky intensification or unmodeled wind shifts not supported by current observations.