A long spell of oppressive humidity and leaden skies over the Río de la Plata is about to be shattered by the most significant cold snap of the year. After nearly three weeks of clinging damp and near-permanent cloud cover, a mass of polar air advancing from the south will scour the atmosphere clean, restoring bright sunshine to the Argentine capital and its metropolitan hinterland. The cost, however, is a plunge in temperatures that weather forecasts suggest will drive minimums down to between three and six degrees Celsius over the coming long weekend, with the wind chill making it feel several degrees colder.

As of Wednesday, the transition was still only a promise. The Área Metropolitana de Buenos Aires woke to dense morning fog banks and a compact ceiling of cloud, the legacy of an intense humid air mass that has dominated the central region. National early-warning systems raised a yellow alert for markedly reduced visibility across the country’s centre, while attention in Patagonia and the Andean cordillera was fixed on fierce wind gusts and heavy snowfall – the very engine of the weather shift that will soon redraw conditions across the pampas. For porteños, the immediate forecast held the threat of isolated showers towards nightfall, with temperatures wedged in a narrow band far above what is about to arrive.

The meteorological pivot will come on Thursday. Analysts tracking the movement of high-pressure systems from Patagonia note that a wedge of cold, dry air will finally begin to displace the stagnant moisture. Sunshine, absent for what has felt like an eternity, is expected to make a sustained return by the afternoon, and by Friday the skies should be largely clear. Yet this clarity is a double-edged sword. With the insulating blanket of cloud stripped away, overnight heat will radiate into space, allowing frost to whiten wide swathes of Buenos Aires province. Highs will struggle to offer much comfort during the day, and the sensation of cold will be amplified by the dry polar wind.

Viewed from a climatological perspective, the coming days mark a textbook – if unusually prolonged – example of the Southern Cone’s winter dynamics. The same mass of air that is frosting Patagonia and lashing the Andes will reshape daily life in one of South America’s largest urban corridors. For a population accustomed to moderate winters, the sharpness of the chill will test infrastructure and patience; agricultural interests will watch tender crops with concern, while energy demand is likely to spike. The sun’s victory over weeks of grey is welcome, but its reign will carry a bite that will linger well beyond the holiday weekend.