N. Italy: 10 °C of difference in 100 km?

Today the maximum temperatures in N. Italy have observed very different values between the north and south of the Po valley. In fact the temperatures observed in the afternoon (Figure1) were close to 10 °C between Veneto and Friuli Venezia Giulia, instead in Emilia Romagna and S. Lombardy the maximum values were close to 0°C, with some areas (e.g. Parma, Piacenza) observing negative values throughout the whole day.

Figure1. Maximum temperatures today 18/12/2018 (source: Meteociel).

The high-pressure system positioned east of Italy has contributed to this significant difference, causing a temperature inversion (colder air at surface) especially in the areas with snow at the ground (Emilia Romagna). The snow has increased the albedo effect which has caused a decrease in the observed temperatures (especially in the minimum values). The second element is the stationary fog (Figure2) in the south of the Po valley which has caused a decrease in the solar radiation (thus in the warming effect) during the day, increasing the temperature difference between the north of the plains and the south. The stationarity was caused by the (weak) easterly winds coming from Slovenia and blowing in N.E. Italy which have decreased the humidity in this area, and have ‘pushed’ the fog towards the northern Appennines. In addition, in the south of the Po valley, the (weaker) winds were mostly south-westerly, and the area where the fog ‘ends’ (limit between foggy conditions and clear sky) was at the convergence of the two different winds.

Figure2. Satellite image of today 18/12/2018 (source: Sat24).

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I am Edoardo and I am passionate about weather analysis and forecasing. I would like to share my knowledge and to learn more with others (both International and Italian community).

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