Recent Met Office and ECMWF ensemble guidance shows an incoming fresher Atlantic airstream and increasing cloud cover that is expected to cap London’s maximum temperature on August 21 at 20–22 °C, aligning with the market’s heaviest weighting on 21 °C. This follows several days of mild conditions and a gradual cooling trend after mid-month warmth, keeping values close to the long-term August climatological average of roughly 21–22 °C. Model spread remains modest, with limited scope for stronger southerly flow that could push readings to 23 °C or higher, while overnight minima and shower risk further constrain daytime peaks. Traders are therefore assigning the highest implied probabilities to the narrow 20–22 °C band pending the next high-resolution model runs and updated Met Office briefings.