Christmas day in Italy has shown both a wintry and mild aspect. Looking at the minimum and maximum temperatures (Figure1), we can see how values below 0°C were observed in the morning in the Po valley and Alpine region, with frost especially in the countryside. Values close to 0 °C were recorded also in central-southern Italy on the Appennines, instead mild values (10-15 °C) were observed mainly in Sicily and Sardinia.
The night and morning has been sunny mostly everywhere; only in Calabria and Sicily some showers have occurred and foggy conditions were observed especially on the plains in N.E. Italy.
The afternoon has been settled mostly everywhere, with sunny conditions along the peninsula. However, in N.E. Italy, especially close to the Adriatic coast (Figure2), foggy conditions have lasted during the whole day, causing cold temperatures in the plains.
Indeed, the maximum temperatures (Figure1) were just above 0 °C in the area between Venice, Verona and Ferrara; instead, in N.W. Italy, were bright conditions have occurred most of the day, maximum temperatures reached 10-11 °C.
Also in central-southern Italy this Christmas has not been cold (though with temperatures close to the average), with maximum values between 10-15 °C mostly everywhere (lower values along the Adriatic coast due to the colder air moving towards the Balkans). Finally, the warmest temperatures were observed in Sardinia and Sicily, with peaks of 16-18 °C in some areas.
The very different temperatures observed were due to both local orography/climate and larger scale weather patterns.
The foggy (and cold) conditions on the plains in N.E. Italy were due to the absence of winds at surface in the area and to anticyclonic conditions in the western Mediterranean region. Moreover, being the area surrounded by mountains (Alps and Appennines), the cold air is ‘trapped’ at surface along with humidity and pollutants (which contribute to the formation of the fog).
Instead, in N.W. Italy, the winds were ‘stronger’ and coming from the Alps, leading to a decrease in the humidity and to an increase in temperatures during the day.
Along the peninsula, the colder air on the Balkans has caused a decrease in temperatures on the Adriatic coast with strong northerly winds; instead, the Tyrrhenian side, ‘protected’ by the Appennines, has seen a little decrease in temperatures.
The minimum and maximum temperatures observed in the main italian cities on Christmas day, compared with the 1971-2000 average, are shown in Table1.
We can see how Venice has observed low temperatures (-3 °C of anomaly in both minimum and maximum values), instead the cities in N.W. Italy (especially Torino) have shown maximum values well above the average (+7 °C of anomaly in Torino). Also the cities on the Adriatic coast (Ancona, Bari) have shown temperatures below the average, though only for the maximum values, instead Roma and Palermo (Sicily) were warmer than the average.
These weather conditions will last until Saturday, with the high-pressure still positioned on W. Europe bringing mild and settled weather on the peninsula (though foggy conditions are still possible in the Po valley with temperature inversion at surface). Then, from Sunday, a colder air mass coming from Scandinavia should cause a decrease in temperatures especially in northern-central Italy. However, it is too early to talk about it in details, especially regarding the likelihood of precipitation (e.g. snow).