On the morning of December 28, 2020, Milan woke up under an impressive blanket of snow, the protagonist of the largest snowfall in the last ten years. The meteorological event involved much of Northern Italy, bringing snow accumulations that, in some areas of the city, reached 25-30 cm. The flakes began to fall from the early hours of the previous day, intensifying during the night and creating an almost surreal scenario with streets, buildings, and parks blanketed in white.
The snow covered the entire Lombardy region and surrounding areas, hindering traffic and causing disruptions to public and private transport, while at the same time offering a suggestive spectacle. This intense snowfall was favored by the presence of the so-called Padano cold cushion, a typical meteorological phenomenon of the Po Valley.
The mass of cold air trapped at ground level, despite the milder temperatures of the overlying air, allowed the snow to accumulate without turning into rain.
A particular influx of icy air from the Alps had already significantly lowered temperatures in the plain, thus creating the ideal conditions for the persistence of snow on the ground. During the daytime hours, the city of Milan experienced continuous snowfall with flakes falling without interruption, a rare event for the Milanese urban area.
The images of a snow-covered Piazza Duomo and the main streets covered by a thick blanket of snow captured a memorable and rare moment in recent meteorological history.
The day of December 28 is remembered for bringing the city back to a winter scenario of bygone times, capable of both astonishing and challenging the means of managing the territory under conditions of intense snow.
It is a mass of very cold air that remains trapped at ground level due to the geographical conformation of the valley and the Alps, which prevent rapid air exchange.
The cold cushion usually forms after periods of high pressure that favor intense cooling of the plain, creating a sort of “lake” of stationary cold air. When oceanic disturbances, loaded with humid and milder air, reach the Po Valley, the cold cushion acts as a barrier, preventing this air from quickly warming the lower layers.
This thermal contrast between the stagnant cold air near the ground and the warmer air arriving from the Atlantic creates the perfect conditions for snowfall.
The snow forms because the humid and warmer air slides over the cold cushion, where it cools and condenses into flakes, without melting into rain. The flat areas of Northern Italy thus benefit from a microclimate that favors winter snow more than other areas with similar latitudes.
Thanks to the cold cushion, the Po Valley can see significant snow accumulations, even with temperatures slightly above zero, while in other regions, the same disturbances would predominantly cause rain.
This mechanism makes the Po Valley one of the few areas of the Italian peninsula where snow frequently settles on the ground during winter, even in the absence of extreme cold conditions.
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