If you start in Lausanne, Switzerland, in December, the weather is chilly here, with temperatures around 0-4°C and occasional snow and rain.
Next, you go to the Italian regions of Vale D'Aosta and Piedmont. The weather remains cold, sometimes even colder than before. It often snows, sometimes mixed with rain.
In Lombardy and Emilia-Romagna, the temperatures may go up a bit, from 0°C to around 5-6°C. Here, it rains more often than it snows, with some sunny days.
In Tuscany, the weather gets a bit warmer, with temperatures up to 7-10°C. You'll have some sunny and cloudy days, with moderate to heavy rain showers.
Finally, you reach Lazio, where the winter is usually mild, with temperatures from 9°C to 12°C. The weather changes often, with sunny days, cloudy days, and lots of rain.
In general, on this trip from Switzerland to Rome, you'll go from snowy cold weather to milder weather with more rain.
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