The market-implied certainty around a 9°C minimum in Buenos Aires on October 12 stems from the day's completion and convergence of official station observations with post-event model verification. Cool, moist southerly flow under persistent cloud cover and light drizzle suppressed daytime heating, yielding a narrow diurnal range consistent with late-spring climatology for the region. National meteorological service data align with this threshold, leaving little room for revision once quality-controlled readings are finalized. Only an undetected sensor malfunction or significant post-processing adjustment could alter the outcome, though such changes are rare for established urban stations.