Recent Met Office guidance points to a daytime maximum of 23°C in London on August 20 amid a post-heatwave cooldown, with scattered showers and variable cloud cover expected to limit solar heating. Ensemble forecasts from global models show a tight cluster around 21–24°C, driven by the precise arrival and persistence of Atlantic frontal systems that introduce moisture and reduce insolation compared with the clearer, warmer conditions earlier in the month. Minor differences in timing of any sunny breaks or shower intensity explain the close market spread between 22°C, 23°C, and 24°C outcomes, as small shifts in boundary-layer mixing or wind direction can alter peak readings by 1–2°C. Updated model runs and official briefings over the next 48 hours will likely tighten or shift this narrow range.