Recent forecasts from the UK Met Office and ensemble models indicate mild overnight conditions for London on May 20, driven by a stable high-pressure pattern and southerly flow that limits radiative cooling. This has elevated the market-implied probability for a minimum of 17°C or higher to 42%, well above the historical late-May average low near 9°C. Shorter-range guidance still shows moderate uncertainty in cloud cover and wind speeds, which could allow dips toward 11–13°C and explain the secondary clustering around those levels. Traders are weighting the absence of strong cold-air advection or clear-sky nocturnal cooling as the dominant factor heading into the final forecast updates.