Map from Google - Italy

In Italy there are different types of climate: mild continental in the Po Valley, cold in the Alps, Mediterranean in coasts and islands, and finally cool and windy in the Apennines. July and August are the hottest and sunniest months, except in the Alpine region where thunderstorms in the afternoon are quite frequent.

Po Valley

Climate of the Po Valley
In northern Italy, the Po-Venetian plain has a moderately continental climate. Relative humidity is high throughout the year, and the wind is normally weak, especially in the west-central part: being closed on three sides, the Po valley is one of the least windy areas in the world.
Precipitation is moderate, between 650 to 1,000 millimetres (25 to 40 inches) per year, typically with two maxima in spring and autumn, and two relative minima in winter and in summer. The average temperature in January, the coldest month, is close to freezing (0 °C or 32 °F) in the western part (see Alessandria and Asti in southern Piedmont), around 1/2 °C in much of the area, while it reaches 2/3 °C (36/37 °F) in the eastern part, namely the Venetian Plain and Romagna. The eastern part, near the Adriatic Sea, is milder in winter, but it is also exposed to outbreaks of cold air from Eastern Europe, brought by the cold wind called Bora; during summer the eastern part it's hot and muggy like the rest of the plain, but at least in the afternoon the breezes blow from the sea.
During winter, from December to February, sometimes snow can fall, particularly in the west (Piedmont, Lombardy) and at the foot of the Apennines (in cities located along the Via Emilia, from Piacenza to Bologna), where 20 to 40 cm (8 to 16 in) of snow per year fall. More rarely, snow can occur in the east, in the plain of Romagna (see Forlì, Cesena). Light frosts at night are frequent in the Po-Venetian plain, while during cold waves, the temperature can drop to a few degrees below freezing, with some chance of frost even during the day: at night it rarely drops below -7 °C (19 °F), but in the coldest winters it can go down to -15 °C (5 °F) and below.
During winter, fog is quite common, especially in the central area, which is crossed by the Po River and distant from mountain ranges (for example, in Cremona, Pavia, Mantua and Ferrara). Fog was more frequent in past decades, until the 80s, when the airport of Milan was the foggiest in Europe, but it has become less frequent in recent years, although it has been replaced by a blanket of low clouds, which often covers the plain during winter, even when in the rest of Italy (including the Alps) a high pressure system brings good weather.
Summer in the Po Valley, from June to August, is hot and muggy, with daily averages around 23/24 °C (73/75 °F), but with a gradual heating in periods of good weather, during which the maximum temperature can rise to around 35/36 °C (95/97 °F). From May to August, thunderstorms in the afternoon or in the evening are fairly frequent at the foothills of the Alps, especially in Piedmont and Lombardy, while they are less frequent in the rest of the plain.
In northern Italy, the shores of the lakes (Maggiore, Como, Garda) are slightly milder and less foggy in winter, while in summer the heat is less intense and quite often broken by thunderstorms. The rainfall amount is high especially in the lakes of the north-west: in Como, where the average in January is 4 °C (39 °F), 1,300 mm (51 in) of rain per year fall, with a maximum in May, of 160 millimetres (6.3 in), and August, of 135 mm (5.3 in); autumn is rainy as well, and sometimes heavy rains can raise the level of the lake.
Northern Italy is protected by the Alps from cold winds: the northerly wind can sweep away the blanket of mist and fog, but descending from mountain slopes, it is heated by compression, giving rise to the Föhn, a dry and relatively warm wind, which blows even more often in the Alpine valleys. Therefore, as mentioned cold spells in northern Italy come from eastern Europe.
In Milan, the average temperature of January is 1 °C (34 °F), that of July is 23 °C (73 °F). In a typical year, 945 millimetres (37 inches) of rain fall, distributed fairly evenly, however winter is the relatively driest season with about 60/65 mm (2.4/2.6 in) per month, while the rainiest are spring and autumn. Here is the average precipitation.
Average precipitation - Milan
MilanJanFebMarAprMayJunJulAugSepOctNovDecYear
MilanJFMAMJJASONDY
Prec. (mm)65658080956570957010010060945
Prec.(in)2.62.63.13.13.72.62.83.72.83.93.92.437.2
Days77888867579686

Sunshine is scarce from November to January, due to fog and low clouds, while it's good in the summer, from June to August, when, however, some Atlantic fronts may still pass, bringing a few rainy days, or more often thunderstorms can develop in the afternoon or in the evening. Here are the average temperatures.
Average temperatures - Milan
MilanJanFebMarAprMayJunJulAugSepOctNovDec
MilanJFMAMJJASOND
Min (°C)-10471215181814940
Max (°C)691417222629292418116
Min (°F)303239455459646457483932
Max (°F)434857637279848475645243

In Turin the temperatures are similar: the average goes from 1 °C (34 °F) in January to 22 °C (72 °F) in July: summer is a bit cooler, both because of the proximity to the Alps and of infiltration of cool air from France. Throughout the year, 915 mm (36 in) of rain fall, with a minimum in January of 40 mm (1.6 in), and a maximum in May of 120 mm (4.7 in).
Venice, on the coast of the Adriatic Sea, is a bit milder, and its average temperature goes from 3 °C (37.5 °F) in January to 23 °C (73 °F) in July. Throughout the year, 750 millimetres (29.5 inches) of rain fall; here snow falls more rarely than in Milan and Turin, and in any case it's not abundant, but the city is exposed to the Bora. In mid-summer, in July and August, Venice is often muggy, except when the Bora blows, during cooler and cloudy days, or when thunderstorms break out in the afternoon.
Average temperatures - Venice
VeniceJanFebMarAprMayJunJulAugSepOctNovDec
VeniceJFMAMJJASOND
Min (°C)014813161818141041
Max (°C)791316222528282418127
Min (°F)323439465561646457503934
Max (°F)454855617277828275645445

Venice

In the northern Adriatic Sea, the water temperature becomes pleasantly warm for swimming in summer, especially in August, although being a small and shallow sea, it may experience remarkable changes depending on weather condition. Here is the sea temperature at Rimini.
Sea temperature - Rimini
RiminiJanFebMarAprMayJunJulAugSepOctNovDec
RiminiJFMAMJJASOND
Sea (°C)121111131822252623201614
Sea (°F)545252556472777973686157

Trieste is outside of the Po Valley and has a relatively mild climate: the average in January is 5 °C (41 °F). However, the city is particularly subject to the Bora, because cold air masses coming from eastern Europe accelerate when they are channeled through the mountain ranges, so the wind rushes to the Gulf of Trieste, with gusts above 100 kilometres (60 miles) per hour, bringing also possible frosts from December to early March. In Trieste, snow is quite rare, because the Bora is originally a dry wind, though sometimes its rarer version called "dark Bora" can bring some snowfalls in winter and some cool and rainy days in summer. Summer is hot and humid, with a July average of 24 °C (75 °F), but tempered by the breezes.
Here are the average temperatures.
Average temperatures - Trieste
TriesteJanFebMarAprMayJunJulAugSepOctNovDec
TriesteJFMAMJJASOND
Min (°C)4471015182020171385
Max (°C)891217222528282318129
Min (°F)393945505964686863554641
Max (°F)464854637277828273645448

Trieste is a quite rainy city: here 1,050 mm (41.5 in) of rain fall in a typical year, and like in Milan, there can be thunderstorms in late spring and summer.

Alps and high mountains

Climate of the Alps
The Alpine Chain, which stretches from west to east, has a mountain climate, cold and snowy in winter, and mild in summer, with frequent thunderstorms. There are several winter sports resorts. In the highest peaks such as Mont Blanc, 4,810 metres (15,781 feet), Monte Rosa and Matterhorn, there are also glaciers. In Italy, the snowline is a bit higher than in the northern side of the Alps, and it's around 3,000 metres (9,800 ft). In general, the west-central part of the Alps, exposed to southern winds, receives the bulk of the snow in late autumn and early winter, while the eastern part is more exposed to northern currents, so it receives most of the snow in winter and early spring.
In Bormio, Lombardy, at 1,200 metres (3,900 feet) above sea level, the average of January is -2 °C (28 °F), and that of in July is 17 °C (63 °F). In Corvara in Badia, in the Dolomites, at 1,500 metres (5,000 feet), the average of January is -7 °C (19 °F), and that of July is 13 °C (55.5 °F). In the weather station of Plateau Rosa, at 3,500 metres (11,500 ft), on the slopes of Monte Rosa, Aosta Valley, the average is between -11 °C (12 °F) in January and 1 °C (34 °F) in July.
Here are the average temperatures of Dobbiaco - Toblach (Alto Adige - Südtirol), located at 1,200 metres (3,900 feet) above sea level, in the Dolomites.
Average temperatures - Dobbiaco
DobbiacoJanFebMarAprMayJunJulAugSepOctNovDec
DobbiacoJFMAMJJASOND
Min (°C)-9-7-304710962-4-7
Max (°C)0371015192221171250
Min (°F)161927323945504843362519
Max (°F)323745505966727063544132

In valleys at the foot of the mountains, at low altitude (see Aosta, Trento, Bolzano), the climate is moderately continental, with cold winters, with an average in January around freezing, and hot summers, but with lower humidity compared with the Po valley, and with cool nights. In winter it can snow, while from May to August, thunderstorms in the afternoon are fairly frequent.

Mediterranean climate

Area having a Mediterranean climate

The climate for which Italy is famous, with a mild climate and plenty of sunshine, is actually found only in coastal and plain areas of the centre and south, as well as in the coast of Liguria in the north-west. The Mediterranean climate is characterized by mild and rainy winters, and hot and sunny summers, a bit muggy but also tempered by breezes. Autumn is often rainy, especially from late September or October onwards.
At a given latitude, the Tyrrhenian coast is slightly warmer than the Adriatic coast.
The Ligurian Riviera has a mild climate, especially in the western part, but it is rainy in autumn and winter. In Sanremo, the average goes from 10 °C (50 °F) in January, to 24 °C (75 °F) in July and August.
Average temperatures - Sanremo
SanremoJanFebMarAprMayJunJulAugSepOctNovDec
SanremoJFMAMJJASOND
Min (°C)77911151821211814108
Max (°C)131315172124272724211614
Min (°F)454548525964707064575046
Max (°F)555559637075818175706157

In Genoa the temperature is similar in summer but it's a bit lower, around 8 °C (46.5 °F) in January. Rainfall follows the Mediterranean pattern, with a maximum in autumn and winter, and a minimum in summer. Throughout the year, 1,080 mm (42.5 in) of rain fall, with a maximum in autumn, of 170 mm (6.7 in) in October. Here is the average precipitation.
Average precipitation - Genoa
GenoaJanFebMarAprMayJunJulAugSepOctNovDecYear
GenoaJFMAMJJASONDY
Prec. (mm)10075809070602570135170110951080
Prec.(in)3.933.13.52.82.412.85.36.74.33.742.5
Days86787535687777

In the capital, Rome, the average temperature goes from 7.5 °C (44.5 °F) in January to 25 °C (77 °F) in July and August. The districts near the sea are milder in winter and a bit cooler in summer, because of the influence of the sea and the breezes that blow in the afternoon. The air is quite humid all year round. Summer is hot and sunny, with occasional thunderstorms in the afternoon. Highs in July and August are around 30/32 °C (86/90 °F), but sometimes they can exceed 35 °C (95 °F).
Average temperatures - Rome
RomeJanFebMarAprMayJunJulAugSepOctNovDec
RomeJFMAMJJASOND
Min (°C)335812161919161285
Max (°C)121315182328313127221612
Min (°F)373741465461666661544641
Max (°F)545559647382888881726154

Due to the urban heat island effect, during the summer months the heat in the centre of the city is more intense. Throughout the year, about 800 mm (31.5 in) of rain fall; the wettest season is autumn, followed by winter. The first part of spring, until April or early May, may have moderate rains as well. In Rome, the summer drought is most evident than in the Ligurian Riviera.
Here is the average precipitation.
Average precipitation - Rome
RomeJanFebMarAprMayJunJulAugSepOctNovDecYear
RomeJFMAMJJASONDY
Prec. (mm)707055806030203065100115100795
Prec.(in)2.82.82.23.12.41.20.81.22.63.94.53.931.3
Days787964236810979

In winter, rainy and cloudy days alternate with sunny days. The north wind, called Tramontana, blows at times, bringing sunny days but also cold nights, with some slight frosts.

Rome

In Naples, the climate is similar to Rome, but more temperate, given its position on the coast, and also a little more rainy in autumn and winter.
South of Naples, along the Tyrrhenian coast, the climate becomes typically Mediterranean, in fact the average in January exceeds 10 °C (50 °F). Sicily is particularly mild and sunny; in summer it's hot in inland hills, while the coasts are hot and humid but tempered by sea breezes. In Palermo, the average temperature goes from 12 °C (53.5 °F) in January to 26.5 °C (79.5 °F) in August; rainfall amounts to 750 mm (29.5 in) per year, with little or no rain in summer. The city is exposed to the warm southern wind called Scirocco (Sirocco), which brings an intense heat in late spring and summer, as well as to the north-westerly wind called Maestrale, which brings cool weather and a bit of rain. In Palermo, as in the rest of the Sicilian coast, it never freezes.
Average temperatures - Palermo
PalermoJanFebMarAprMayJunJulAugSepOctNovDec
PalermoJFMAMJJASOND
Min (°C)9910111519222320171310
Max (°C)151516192327303128241916
Min (°F)484850525966727368635550
Max (°F)595961667381868882756661

In Cagliari, Sardinia, the average temperature in January is 10 °C (50 °F), while in July and August it's 24 °C (75 °F).
Average temperatures - Cagliari
CagliariJanFebMarAprMayJunJulAugSepOctNovDec
CagliariJFMAMJJASOND
Min (°C)667912161920171497
Max (°C)141517192327303127231815
Min (°F)434345485461666863574845
Max (°F)575963667381868881736459

Rainfall in Cagliari is quite scarce: just 430 millimetres (17 inches) per year, but still with a Mediterranean pattern, therefore, with a minimum in summer. Here is the average precipitation.
Average precipitation - Cagliari
CagliariJanFebMarAprMayJunJulAugSepOctNovDecYear
CagliariJFMAMJJASONDY
Prec. (mm)45554535251031030555555425
Prec.(in)1.82.21.81.410.40.10.41.22.22.22.216.7
Days88764211468862

The temperature of the sea in Sardinia, as generally happens in central Mediterranean Sea, is warm enough for swimming in summer, with a peak in August.
Sea temperature - Porto Cervo
Porto CervoJanFebMarAprMayJunJulAugSepOctNovDec
Porto CervoJFMAMJJASOND
Sea (°C)141414141720232523201815
Sea (°F)575757576368737773686459

Sardinia is a mild and sunny region, but it's quite windy because of the Maestrale (Mistral), a cool and dry northwest wind, which blows especially in winter and spring, and can bring sea storms on the western side of the island and in the Strait of Bonifacio. In inland areas, however, there are highlands, where the winter temperature drops by a few degrees, becoming a little cooler, so that this area falls within the climate of Central Italy (see below).
On the Adriatic coast, even in Bari, Apulia (Puglia), the climate is Mediterranean, with fairly low rainfall, typically below 600 mm (23.5 in) per year. Apulia is exposed to the Scirocco, but also to outbreaks of cold air masses from the Balkan Peninsula, which sometimes can arrive here, lowering the temperature in winter, and bringing snowfalls especially on inland hills.
The southernmost islands (Pantelleria, Lampedusa) are very mild in winter, so that it never freezes nor snows, but they are windy and sometimes rainy. Summer is hot and sunny, but tempered by breezes, and longer than elsewhere.

Sardinia

As mentioned, in central and southern Italy, sometimes the Scirocco blows, a dry and warm wind from Africa, which can bring dust or even sand in the southernmost regions. When this wind is not too strong, it has the time to pick up moisture from the sea, becoming quite humid. The Scirocco is more frequent in spring and autumn, but it may blow in all seasons, and can raise the temperature above 20 °C (68 °F) in winter in the south, while in late spring and summer it brings heatwaves, with peaks of 40 °C (104 °F), and sometimes even above, especially in Sicily and Apulia.

Central Italy

Climate of central Italy

In central Italy (Tuscany, Umbria, Marche), the climate is transitional, a little too cold in winter to be considered Mediterranean.
In Florence, the average January temperature is 6 °C (43 °F), and sometimes at night it drops below freezing. Summer is hot, sometimes torrid during the day, when the temperature can reach 36/38 °C (97/100 °F), even though the air is not too humid and nights are usually cool.
Average temperatures - Florence
FlorenceJanFebMarAprMayJunJulAugSepOctNovDec
FlorenceJFMAMJJASOND
Min (°C)225712151818141053
Max (°C)111316192428313227211511
Min (°F)363641455459646457504137
Max (°F)525561667582889081705952

The region of Marche is a little milder in summer, while in winter it's exposed to cold air masses from the Balkan Peninsula, with possible snow on inland hills and sometimes even on the coast. In Umbria, during winter the north wind (Tramontana) often blows. The hills of Tuscany have generally a mild climate, with winters a bit cold above 300 metres (1,000 feet), and hot and sunny summers, but tempered by breezes, except in some sheltered valleys, which may be very hot. Snow, though rare, is not unheard of in winter, from December to February.

Apennines

Climate of the Apennines

The Apennine Range is stretched along the Italian peninsula from Liguria, where it separates the mild Riviera from the more continental Po Valley, to the south. In cities located in the Apennines, in central and southern Italy, in the regions of Abruzzo, Molise, Campania, Basilicata and Calabria, the climate is moderately continental, with cold winters, sometimes snowy, and warm and sunny summers, with some chance of thunderstorms in the afternoon.
In L'Aquila, in central Italy (Abruzzo), located at 700 metres (2,300 feet) above sea level, the average temperature goes from 2 °C (35.5 °F) in January to 21 °C (70 °F) in July. Throughout the year, 700 mm (27.5 in) of rain fall, with a maximum in autumn and a minimum in summer. During winter it can snow and freeze, and the temperature can drop to -10/-15 °C (5/14 °F).
In Potenza, southern Italy (Basilicata), 850 metres (2,800 ft) above sea level, the average temperature goes from 4 °C (39 °F) in January to 21 °C (70 °F) in July and August. During winter and early spring, snowfall is possible, while in summer the Scirocco can sometimes raise the temperature up to 35 °C (95 °F).
Average temperatures - Potenza
PotenzaJanFebMarAprMayJunJulAugSepOctNovDec
PotenzaJFMAMJJASOND
Min (°C)1135913151613952
Max (°C)771013182226262217118
Min (°F)343437414855596155484136
Max (°F)454550556472797972635246

Above 1,000 metres (3,300 feet), the climate gets colder, and during winter there can be heavy snowfalls. Here are the average temperatures of Mount Terminillo, located in the central Apennines, whose summit is at 2,217 metres (7,274 feet), though the weather station is located at 1,875 metres (6,150 feet).
Average temperatures - Terminillo
TerminilloJanFebMarAprMayJunJulAugSepOctNovDec
TerminilloJFMAMJJASOND
Min (°C)-4-4-3-147111174-1-3
Max (°C)1124913171713942
Min (°F)252527303945525245393027
Max (°F)343436394855636355483936

In the mountains of Sicily, the climate is definitely milder. The cities located at 1,000 metres (3,300 feet) are a bit foggy and windy in winter (see Enna). However, on the highest peaks, such as Mount Etna, which is the highest volcano in Europe with its 3,343 metres (10,968 feet), in winter snow often falls. In Sardinia, in the massif of Gennargentu, at high altitudes the climate is similar to that of the Apennines as well.

When to go

The best time to visit the main Italian cities is the spring: from mid-April to late May, temperatures are pleasant, the days are quite long, the sun often shines and the nature is in bloom, though sometimes it can rain. Another good period is the first half of September. Between mid-September and mid-October, temperatures are good, but it can rain, especially in the north and centre of the country. November is typically a rainy month throughout Italy, even though the sun still shines quite often in the south. In early spring, from March to mid-April, the weather can be sunny and mild, but also cold and wet: it's a fairly unstable period.
Summer, from June to August, is often sunny, but it can be very hot, especially in July and August; however, visitors flock to cities like Rome and Florence even in this period. In any case, it is better to advise those who don't like the heat.
The Alpine areas can be visited in the summer. For skiing, in February and the first half of March, the snow is almost always guaranteed and the days are longer than in December.
For swimming and sunbathing, July and August are good in the north and cente, and also September in the south. In June, the weather is often nice, but the sea can be still a little cool: as mentioned, the water temperature reaches 20/21 °C (68/70 °F) in June, and 24/25 °C (75/77 °F) in July and August.

What to pack

In winter: in Milan, the Po Valley and the Apennines: warm clothes, sweater, down jacket, hat, gloves and scarf, raincoat or umbrella. In the centre, Florence and Rome: warm clothes, sweater, coat, raincoat or umbrella. In Palermo and the Sicilian coast: clothes for spring and autumn, sweater, jacket and raincoat. In the Alps: mountain clothing.

In summer: in the north, Milan and Venice: light clothing, t-shirt, sweatshirt or sweater, light jacket, raincoat or umbrella. In the centre, Rome and Florence: light clothing, sun hat, a sweatshirt for cool evenings especially in June, possibly an umbrella. In the south, light clothing, sun hat, a sweatshirt for the evening especially in June.
In the mountains, sweater, jacket, hiking shoes, raincoat, sunscreen and sunglasses.