The market's overwhelming consensus on a 17°C high for Paris on October 9 stems from official meteorological observations confirming that maximum temperature, aligning closely with the long-term average high of 17.7°C for the date. Mild autumn conditions prevailed with no significant heat advection, clear skies, or urban heat island amplification pushing readings higher, while minimums near 8–11°C kept the daily range typical. Trader positioning reflects verified station data rather than forecasts, with near-certainty arising because post-event verification leaves little room for revision. Only an unprecedented reanalysis discrepancy or alternate station selection could shift the outcome, though such adjustments remain rare for resolved daily temperature markets.