Official forecasts from the UK Met Office and supporting models indicate a maximum of 21°C for London on October 1 under sunny intervals, light westerly winds, and negligible precipitation risk, placing the day well above the 1991–2020 average high of 17.9°C. Stable high-pressure conditions and minimal cloud cover have driven afternoon warming to the low 20s Celsius in recent observations, with hourly trends showing peaks near 20–21°C and little model divergence. This consensus underpins the strong market-implied probability for 21°C, while the secondary weighting toward 20°C reflects residual uncertainty in exact peak timing and localized variations before resolution.