**Forecast models and observational data position the lowest temperature in London on September 1, 2026, most likely in the 12–14°C range, with 13°C carrying the highest market-implied probability at 40.5%.** Short-range guidance from sources such as the Met Office, GFS ensembles, and specialized sites consistently shows overnight minima near 12–13°C (roughly 54–55°F) under building high pressure (around 1020–1030 mb) and light-to-moderate westerly or southwesterly winds. These conditions favor gradual radiative cooling after sunset but limit deeper drops because mild Atlantic air keeps the boundary layer from cooling sharply. Climatologically, early-September London minima average near 12–14°C; current guidance sits close to this baseline after earlier long-range outlooks had hinted at possible warmer anomalies or late-season warmth. Recent model runs have stabilized rather than shifted dramatically, with no strong signals for either an unusually cold northerly flow or persistent cloud cover that would raise the minimum. Traders appear to be weighting the tight clustering of deterministic and ensemble forecasts around 13°C, while assigning lower but non-negligible probability to 12°C or 14°C depending on exact timing of any clearing or wind changes. Upcoming Met Office and ECMWF updates over the next 24–48 hours will refine cloud cover, wind speed, and dew-point details that directly control the precise minimum; any late-model cooling bias or clearer-sky signal could nudge probabilities toward 12°C, whereas stronger mixing would favor 14°C or slightly higher. The market’s heavy concentration on 12–14°C therefore reflects both the current scientific consensus and the limited time remaining for major forecast revisions.