A mass of Antarctic air swept across southern South America on Thursday, delivering rare snowfall to parts of central and eastern Argentina and triggering floods in southern Brazil. In Argentina, the cold prompted school closures in Mendoza province and left several coastal towns in Buenos Aires province dusted with snow. In Brazil, an associated extratropical cyclone drove heavy rains that pushed the Uruguay River above flood stage in the border city of São Borja, forcing at least one family from their home.

Argentina’s National Meteorological Service (SMN) maintained yellow alerts for extreme cold across 18 provinces, warning of temperatures well below seasonal norms. In Mendoza, provincial education authorities suspended all in-person classes after overnight snow and ice made roads treacherous. Snowfall was confirmed in the Buenos Aires province localities of Tres Arroyos, Lobería, and Sierra de los Padres, and in the coastal city of Mar del Plata, where residents shared images of a thin white layer—the first such event in 22 years, according to local meteorological records, though some accounts cited a 35-year gap since the last significant accumulation. In Brazil, civil defence officials in Rio Grande do Sul reported that eight municipalities suffered damage from storms and flooding, with the Uruguay River reaching 9.02 metres in São Borja, exceeding the official flood threshold. A family and a commercial establishment were evacuated, and two people remained displaced.

Forecasters in both countries said the cold core would linger through the weekend, with temperatures in parts of Patagonia and the Argentine pampas expected to drop as low as -9°C. In the Buenos Aires metropolitan area, the SMN predicted a minimum of 0°C for Friday, with the possibility of frost in outlying suburbs. Brazilian meteorologists warned that the cyclone would continue to generate high winds and rough seas along the southern and southeastern coasts, with waves potentially reaching four metres off Rio de Janeiro state. The Uruguay River was expected to stabilise temporarily before rising again, prompting Porto Alegre’s civil defence to issue a preventive hydrological alert for Lake Guaíba, though no flooding was imminent.

Authorities across the region urged residents to limit outdoor exposure and to monitor official channels. In Mendoza, officials said the decision to extend school suspensions would be reviewed on Friday morning. In Rio Grande do Sul, emergency services remained on standby as river levels were projected to fluctuate in the coming days.