Official measurements from Meteo-France stations confirmed a maximum temperature of 16°C in Paris on May 16, driving the market's 100% implied probability for that exact outcome. Stable high-pressure systems over western Europe combined with moderate northwesterly flow kept daytime heating modest, well below the typical mid-May average of 18–20°C for the Paris region. European Centre for Medium-Range Weather Forecasts model runs showed tight consensus on this range in the final 48 hours, with no significant warm-air advection or urban heat-island amplification under clear skies and light winds. While post-event data revisions remain theoretically possible, the alignment of surface observations and reanalysis products leaves little room for adjustment, underscoring why traders assigned near-certainty to the 16°C threshold.