The rain, the cold and the snow return
The irruption of icy air that hit Northern Italy on Friday 19 January will move towards the Centre-South in the next few hours, bringing a significant drop in temperatures, strong gusts of wind, but also snow, thunderstorms and snow showers (graupel). Another very busy day for much of Central Italy, and especially in the areas of the medium-lower Adriatic coast.
Between the night and the early morning of Saturday 20 January the first effects of the icy outbreak will be noticed starting from the Marche and Abruzzo regions, with showers or rain showers along the coastal areas and snowfalls up to 3-400 meters above sea level. As the hours pass, the bad weather will extend across the entire mid-lower Adriatic, affecting Molise, Puglia, Basilicata, Campania and finally also Calabria. Strong snowstorms and sustained gusts of wind are expected across the entire Apennines, from Abruzzo to Basilicata. Freezing weather! The weather will always be disturbed but slightly milder on the Tyrrhenian side, with showers and showers which will also affect lower Lazio and Campania. The white lady could fall up to 6-700m just outside Naples, giving a dusting of snow even to the slopes of Vesuvius.
The snow may further lower its altitude between the late morning and early afternoon of Saturday 20th. The entry of even colder air will favor not only snowfall at altitudes close to the plains, but also sudden showers or thunderstorms on the coasts of Puglia, where no possible places and places whitened by the characteristic phenomenon of the ‘gragnola’ or ‘graupel’ are excluded. Precipitation pattern: the graupel or ‘gragnola’ Let’s first of all try to understand what it is. Its official name is Graupel, a German word which is the Italian equivalent of “granella” or “gragnola”. As we can see from the diagram below, the graupel is nothing more than a snowflake that has lost its initial structure. During its descent and in a context of turbulent air motion, it comes into contact with minute droplets of supercooled water (liquid water at temperatures below zero) which solidify in contact with the crystal, forming a thin crust around it of ice.
The result is therefore a mix between an old snow crystal and frozen water. Once fallen to the ground, these pellets will tend to bounce (unlike classic snowflakes) and in cases of more intense rainfall, an accumulation of several centimeters of round snow can also form on the ground.
The phenomenon is often associated with thunderstorms, the typical result of strong winter thermal contrasts when arctic or polar air masses meet warm marine or even lake surfaces which favor the onset of convective instability.