**Mild overnight conditions with minimal radiative cooling have driven the near-certain market consensus around a 16°C low for London on September 11, 2026.** Official observations from stations such as London City Airport recorded early-morning temperatures holding at 16–17°C under partly cloudy skies and light southwesterly winds, while Met Office guidance and model consensus projected a diurnal minimum near this level rather than the seasonal average low of about 12°C. Stable high pressure and above-average warmth have prevented the stronger nocturnal drops typical in clearer, calmer anticyclonic setups. The implied probability above 99% reflects this tight observational agreement and the limited remaining hours in the calendar day. A realistic shift would require an abrupt, unforecasted surge in clear-sky longwave radiation loss or a sharp wind shift introducing colder air, neither of which current guidance supports.