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The two warmest months are in Venice, as almost everywhere in the northern hemisphere, July and August. Then the temperatures rise almost every day to over 25 degrees, on almost half of the days even to over 30 degrees. Tepratures over 35 degrees are rather rare at the sea in northeast Italy, but occur. At night it cools only a little in midsummer. On about 20 nights a year, the thermometer does not drop below 20 degrees. These so-called tropical nights are very rare in England, but frequent in Venice.
A winter day can be very different in the lagoon city. On approximately 30 days in the year there is frost in Venice, thus temperatures below 0 degrees in the night. Also under -5 degrees at night occur from December to February. But there are also many beautiful winter days in Venice with sunshine and a temperature of more than 10 degrees.
Spring and autumn are ideal for a city holiday in Venice. In May, June, September and October you can expect temperatures from 18 to 25 degrees during the day. At night between April and October the temperature rarely falls below 10 degrees.
In contrast to the southern Mediterranean, it rains relatively frequently in Venice in summer. The number of rainy days is approximately evenly distributed over the year. It rains about every third day at least for a short time. Also the amount of rain is evenly distributed over the year at the morthern Adriatic Sea.
However, the notorious flood (Acqua Alta) occurs mainly in winter. Then large parts of the old town are flooded, a visit to Venice is only possible to a limited extent. The floods usually last only a few hours.
However, the Acqua Alta is relatively frequent (up to 20 times a year). The solution is a gigantic flood protection system (name: Mose or M.O.S.E), which is to be completed around 2019 (as of the beginning of 2018). More on the subject of flooding in Venice
Water temperatures Venice
Those who want to swim in Venice should know that the water around the city is relatively cold in spring. The sea has over 20 degrees only from approximately the beginning of June until the end of September. Especially in the first half of May, the air during the day is often already over 20 degrees warm, but the sea water is still bitterly cold (around 15 degrees).
Bathing and swimming in the canals of the old town of Venice is strictly forbidden. Even a naked upper body can be punished. But Venice has good beaches. By far the most famous is on the island of Lido, less than half an hour by public transport from the famous Piazza San Marco and the surrounding sights.
Extreme heat in Venice
This is, as I said, rather rare. But there were sometimes temperatures of over 40 degrees in Venice. Also the nights can be very hot. Some people can sleep badly in Venice during the hot nights without air conditioning. Very hot nights are most common from about 10 July to 25 August.
Cold and snow in Venice
As I said, especially at night frost is quite common in Venice in winter. Snow also falls, but rather rarely. Often, but not always, the snow melts again during the day. Permafrost of several days is very rare in Venice. Since people in Italy are not so used to snow, the chaos in Venice is often big when there is snow. Many cars do not have winter tires, the clearing services are not very numerous. In addition, snowploughs can hardly reach the old town because of the many bridges with stairs. But the frequent high water in the oldtown is by far the bigger problem in winter.
Video on the subject of flooding in Venice