**The market's near-certain pricing on -1 °C or below for Buenos Aires' September 13 low reflects the definitive official minimum recorded by Argentine meteorological stations after a strong cold-air outbreak.** High-pressure ridging and southerly winds advected polar air across the Pampas, producing clear skies and rapid nocturnal radiational cooling that drove the overnight low well below freezing. This outcome aligns with model consensus from the prior 48 hours and exceeds typical early-spring minima. Only a post-event revision of station data or an undocumented sensor malfunction could alter resolution, both of which remain exceedingly rare.