Ensemble forecasts from the Met Office and European Centre for Medium-Range Weather Forecasts currently position London’s overnight minimum on May 20 near 8–10 °C, driven by a north-westerly flow of cooler maritime air and extensive cloud cover that limits radiative cooling. This places the greatest implied probability on the 17 °C-or-higher outcome at 50 percent while still assigning meaningful weight to single-digit values, reflecting model spread in the timing of any clearing skies. Historical May climatology shows average overnight lows of 8–9 °C, so the current setup sits close to seasonal norms yet carries uncertainty from possible brief high-pressure ridges that could allow temperatures to dip further. Updated model runs and Met Office briefings over the next 48 hours will narrow the range and are likely to shift trader positions ahead of the 20 May resolution.