Current forecast models from the Met Office and ECMWF indicate significant uncertainty in overnight minimum temperatures for London on May 21, driven by variable cloud cover and potential radiative cooling under clear skies. Ensemble runs show a wide spread, with some solutions favoring calm conditions that could allow the mercury to dip to 7°C or below, while others point to milder southerly flow keeping lows near or above 17°C. Historical May climatology places typical overnight lows around 8–10°C, but shifting high-pressure patterns and Atlantic moisture could alter this baseline. Traders are closely monitoring the next model updates and surface observations for clearer signals on wind speeds and humidity, which directly influence how far temperatures fall after sunset.