Recent Met Office and ECMWF ensemble forecasts indicate London’s overnight minimum on May 17 will most likely settle between 9 °C and 11 °C, positioning the 11 °C outcome as the clear market leader at 84.5 %. A mild southwesterly flow of Atlantic air is limiting radiative cooling under variable cloud cover, reducing the potential for sharper temperature drops that typically occur with clear skies and calm winds. This setup aligns closely with the historical May average low of roughly 9 °C recorded at Heathrow, though model spread centers on differences in predicted cloud timing and boundary-layer mixing. Traders appear to be weighting the upper end of the guidance, reflecting confidence in the dominant air mass while acknowledging the narrow uncertainty band that could still shift the final reading by a degree.