Recent Met Office and ECMWF ensemble forecasts indicate London’s minimum temperature on May 17 will most likely fall between 9 °C and 11 °C, driven by mild southwesterly flow advecting Atlantic air masses across southern England. Variable overnight cloud cover is the key differentiator: clearer intervals permit stronger radiative cooling and potential dips to 9 °C, while increased low-level moisture and light winds limit heat loss and hold readings near 11 °C. This range aligns closely with the long-term May average minimum of roughly 9 °C at Heathrow, with model spread centered on boundary-layer mixing and cloud timing. Traders have concentrated probability on the 9–11 °C outcomes ahead of tonight’s 00Z runs, which should further constrain uncertainty before official Met Office observations resolve the market.