Turin, where it's located

In Turin, capital of Piedmont, the climate is moderately continental, with cold and damp winters, and hot and muggy summers. The city is located at 250 metres (800 feet) above sea level, at the foot of the Alps, along the Po River, in a position that in summer makes it a bit less hot than the rest of the Po valley, and in winter a little less foggy.
Here are the average temperatures of the Caselle Airport.
Turin - Average temperatures
Min (°C)-3-136101417171372-2
Max (°C)791317212528272317118
Min (°F)273037435057636355453628
Max (°F)454855637077828173635246

Precipitation is quite abundant, given that it amounts to nearly 1,000 millimetres (40 inches) per year. The least rainy season is winter, while the wettest periods are late spring, mainly because of afternoon thunderstorms (May is the wettest month), and autumn. However, thunderstorms can occur in summer as well.
Here is the average precipitation.
Turin - Average precipitation

Winter, from December to February, is cold and wet. The sky is often cloudy, and in anticyclonic periods fog may form, although less frequently than in Milan and other areas of the Po Valley. In the middle of the day the sun can come out.
There is a moderate amount of rainy days, although winter is the least rainy season.
The wind is generally weak or absent, except when the föhn blows, a warm and dry wind that comes down from the Alps and is able to bring clear skies and good visibility; in these cases the temperature can reach or exceed 15 °C (59 °F) even in winter.
Snow generally falls at least once every year, although it is seldom very abundant; in amounts on average to 25 centimetres (10 inches) per year. Every now and then, cold air masses from Eastern Europe can bring frosts, more or less intense; in February 2012 the temperature dropped to -14 °C (7 °F).

Spring in Turin is initially an unstable season, in which the first mild days alternate with the return of cold periods, and gradually becomes more enjoyable, especially from mid-April to late May, when there are many nice days, with mild or pleasantly warm temperatures during the day, although thunderstorms may break out in the afternoon or in the evening.
However, Atlantic depressions able to bring rainfall are quite frequent.

Summer, from June to August, is hot and muggy, and generally sunny. Even though the wind is generally weak, the heat is bearable more often than in the rest of the Po Valley, due to the temperature a bit lower, but also to thunderstorms, associated with wind gusts, which affect the city quite frequently, especially in the afternoon and in the evening. There's still some chance of some Atlantic disturbances, which can bring some pretty cool and rainy days even in midsummer (but especially in June and late August).

Autumn gives some nice days in September, and sometimes in early October, then quickly becomes gray and rainy. The first cold days usually occur in November.

Turin, the Mole Antonelliana and the Alps

The amount of sunshine in Turin is not very good from mid-October to February, when the sun comes out quite rarely (but it goes better than in Milan). The sun however is not missing in spring, and is frequent in summer, except during the rare rainy days, and during the more frequent thunderstorms of the afternoon or the evening.
Turin - Sunshine

On the hills that lie to the east of Turin, beyond the Po River, the climate is milder, because in winter they are often above the layer of cold air that stagnates in the Po Valley, while in summer they are cooler because of the higher altitude. Here for example, the average temperatures of the Bric della Croce station, 700 metres (2,300 feet) above sea level, in the municipality of Pecetto Torinese.
Bric d. Croce - Average temperatures
Min (°C)01461014171714941
Max (°C)67111418222524201496
Min (°F)323439435057636357483934
Max (°F)434552576472777568574843

When to go

The best times to visit Turin are spring and early summer, in particular from mid-April to mid-June. September, too, is a good month. However, you have to take into account some rainy days in both periods.
Summer can be hot, although less frequently than in the rest of the Po valley, in fact, there can be several acceptable days, especially in June. You have to take into account, in late spring and summer, sudden thunderstorms in the afternoon or in the evening.