Recent Met Office guidance and ensemble forecasts indicate mild overnight conditions for London on May 21, with minimum temperatures likely settling between 11°C and 14°C under partly cloudy skies and light southeasterly winds. These factors reduce radiative cooling compared with clear, calm nights that historically drop mid-May lows to 7–9°C. Persistent Atlantic flow and limited high pressure favor the warmer end of the distribution, though model spread on cloud timing introduces uncertainty that keeps the 7°C-or-below and 17°C-or-higher buckets nearly tied at 41% each. Updated short-range runs and official station data from Heathrow will refine resolution probabilities over the next 48 hours.