Ensemble forecasts from the Met Office and European Centre for Medium-Range Weather Forecasts place London’s maximum temperature for May 18 near 14–16 °C, driving the market’s leading implied probabilities of 38.5 % for 15 °C and 31.5 % for 14 °C. A broad Atlantic low-pressure system is bringing scattered showers and moderate westerly winds that reduce daytime solar heating and increase turbulent mixing, keeping surface temperatures in check. Small variations in shower timing, cloud cover, or wind direction can easily shift the realized high by 1–2 °C, which accounts for the meaningful share assigned to 16 °C. This spread aligns with typical model uncertainty in an unsettled spring pattern, and the next official guidance updates will further narrow the range ahead of observations at standard London stations.