Recent ECMWF ensemble guidance for Paris shows overnight minima centered near 9–11°C on May 20 under a mild spring regime with moderate Atlantic flow. This distribution underpins the market’s spread, where 11°C holds the second-highest implied probability while 16°C+ leads slightly, reflecting uncertainty in radiative cooling versus cloud cover. Clearer skies overnight would enhance surface heat loss and favor the lower bins, whereas increased low-level moisture or a weak warm advection would push readings toward 12–14°C. Historical May climatology places typical lows around 9°C, so the tight clustering of mid-teens outcomes captures the realistic range before the final model runs and observational updates arrive.