Recent Met Office and ECMWF ensemble guidance points to a maximum of 21–22 °C in London on 22 August under building high pressure that favors sunny intervals and light winds, keeping values near the long-term August mean. Limited daytime heating from partial cloud and modest northerly flow prevents stronger warming, while model spread in boundary-layer mixing and insolation produces a tight cluster of solutions between 21 °C and 23 °C. Trader consensus reflected in the 35 % and 27 % implied probabilities for 22 °C and 21 °C therefore tracks the narrow forecast envelope, with the smaller probabilities assigned to 23 °C or 24 °C capturing the low but non-zero chance of clearer skies or a warmer bias in late guidance runs.