Recent ensemble forecasts from the UK Met Office and ECMWF place London's overnight minimum on September 28 in a narrow 12–15°C range, producing nearly even market-implied odds for 13°C and 14°C. Light winds, variable high cloud, and moderate humidity are limiting radiative cooling rates, while London's urban heat island adds roughly 1–2°C compared with rural sites. Historical September minima average near 12°C, so current conditions sit slightly above the long-term baseline. The tight spread between the two leading outcomes reflects modest differences in model timing of cloud breaks and boundary-layer mixing; the next Met Office update and final overnight observations will resolve the outcome.