Map from Google - Lugano

In Lugano, located in the canton of Ticino, on the shores of the lake of the same name (also called Ceresio), 270 metres (885 feet) above sea level, the climate is temperate, with cold winters (but not freezing), and warm summers, quite sunny but also accompanied by quite frequent thunderstorms. Along with Locarno, Lugano is the mildest location in Switzerland.
In the cold half of the year, the wind is generally weak or non-existent, except when the favonio (or föhn) blows, the warm, dry wind that comes down from the Alps and is able to bring clear skies and very good visibility. During the warm half of the year, the wind is weak or moderate and follows the breeze regime: during the warmest hours the breeze blows from the lake towards the reliefs, while after sunset and at night it blows from the mountains to the lake.
Here are the average temperatures.
Average temperatures - Lugano
LuganoJanFebMarAprMayJunJulAugSepOctNovDec
LuganoJFMAMJJASOND
Min (°C)125812151817141052
Max (°C)791316202427262217117
Min (°F)343641465459646357504136
Max (°F)454855616875817972635245

The rains in Lugano are abundant, since they amount to 1,550 millimetres (61 inches) per year. Winter is the relatively drier season; in spring and autumn the rains are plentiful in periods of Atlantic depressions, due to high altitude southern currents which then climb the Alps, while in late spring and summer, thunderstorms in the afternoon or evening are quite frequent (and sometimes intense). During the most intense waves of bad weather, which occur in autumn (but sometimes also in spring), the lake's water may overflow, flooding the lower areas of the city.
Here is the average precipitation.
Average precipitation - Lugano
LuganoJanFebMarAprMayJunJulAugSepOctNovDecYear
LuganoJFMAMJJASONDY
Prec. (mm)655080155195165155160185140125801560
Prec. (in)2.623.16.17.76.56.16.37.35.54.93.161.4
Days556111310810898698

Winter, from December to February, is cold enough, but it is milder than in the major cities of Switzerland, and even than in the Po Valley, because of the warming influence of the lake. Even fog is less frequent.
There's no shortage of rainy days, even though winter is the relatively drier season. Snow generally falls at least once every year, and sometimes may be plentiful (eg in the 27th of January 2006, 72 cm or 28.5 inches of snow fell), but tends to melt soon enough, because it occurs in conditions of wind from the south. In a year, an average of 26 cm (10.2 in) of snow falls. The record belongs to the winter of 1977/78, when a total of nearly three metres of snow fell.
We can not exclude very cold periods, with night frosts and temperatures around freezing or even below in the daytime; however, in these cases the weather is usually dry. It's rare for the temperature to drop below -5 °C (23 °F), even though it can happen on colder winters; here are some values recorded in the past: January 1985: -10 °C (14 °F); February 1991: -11 °C (12 °F); February 2012: -13 °C (9 °F).

Summer, from June to August, is warm, and often sunny in the morning. The temperature is generally pleasant or at least bearable, also there's some wind because of the lake breezes. Sometimes an Atlantic front, able to bring some cool and rainy days, can pass; more often, thunderstorms can break out in the afternoon or in the evening. We can not exclude some hot days, with highs around 32/33 °C (90/91 °F); more rarely, higher values can be reached, for example in July 1983 and in August 2003 the temperature reached 37 °C (99 °F).

The amount of sunshine in Locarno is acceptable in winter, when there are sunny days alternating with cloudy periods (in January there are 4 hours of sunshine per day); in the other seasons however it is not very high, because in spring and autumn Atlantic disturbances pass quite frequently, while in periods of good summer weather, cloudiness in the afternoon can form, which can lead to thunderstorms: in July, the sunniest month, there are 8.2 hours of sunshine per day on average (in about 16 hours of daylight, so the sun can be seen for a little more than half of the time).

Lugano


The best periods to visit Lugano are spring and early summer, particularly from mid-April to mid-June. Also September is a good month. You should however take into account some rainy days in both periods.
Summer, which is the best time for sunbathing, can be hot, though this rarely happens: usually the temperatures are acceptable, especially in June. Remember the possibility of afternoon or evening thunderstorms, in summer and in May.