Latest Met Office guidance points to a daytime maximum of 22 °C across London on 22 August, anchoring the market’s leading 35.5 % probability for that outcome while the tight clustering around 21–23 °C reflects residual model spread. A weakening high-pressure ridge is yielding to Atlantic low-pressure systems that introduce variable cloud cover and light showers, limiting afternoon heating and keeping peak temperatures near the long-term August average of 22 °C. Ensemble runs show only modest differences in boundary-layer moisture and wind speed that could nudge the recorded high one degree either way at official stations such as Heathrow. With resolution just 48 hours away, traders are watching the next Met Office and ECMWF updates for any shift in cloud or precipitation timing that would alter the precise peak.