Recent Met Office guidance and ensemble forecasts indicate a predominantly westerly airflow across southern England on September 3, with low pressure to the northwest allowing modest warm-air advection from the continent while maintaining cloud cover and scattered light showers. This setup typically produces daytime maxima in the 21–26 °C range, modulated by the precise timing of any breaks in cloud and boundary-layer mixing under 10–15 kt southwesterly winds. Model spreads arise from uncertainties in cloud thickness and frontal timing, which can alter peak insolation by several degrees. Historical early-September climatology for London shows a mean daily maximum near 20–22 °C, so current guidance sits slightly above average yet well below heatwave thresholds, explaining the broad, evenly matched market-implied probabilities across the mid-20s. Updated high-resolution runs and Met Office briefings expected in the next 24–48 hours will likely narrow the range.