Map from Google - Paris

The climate of Paris and the region of Île-de-France is temperate and is influenced by the Atlantic Ocean: it is cold but not freezing in winter, and pleasantly warm in summer; however, it receives some continental influences, so it can sometimes be very cold in winter and hot in summer.
Here are the average temperatures.
Average temperatures - Paris
ParisJanFebMarAprMayJunJulAugSepOctNovDec
ParisJFMAMJJASOND
Min (°C)22571013151512953
Max (°C)781216202325252116118
Min (°F)363641455055595954484137
Max (°F)454654616873777770615246

Precipitation is not abundant, since it amounts to 650 millimetres (26 inches) per year, but it is well distributed over the seasons, however, the rains are a bit more frequent in winter, and a bit more abundant in summer.
Here is the average precipitation.
Average precipitation - Paris
ParisJanFebMarAprMayJunJulAugSepOctNovDecYear
ParisJFMAMJJASONDY
Prec. (mm)504050506550605550605060640
Prec. (in)21.6222.622.42.222.422.425.2
Days10910910987891011110

In winter, from December to February, the average temperatures are quite low: normally, highs are around 7/8 °C (45/46 °F).
The temperature can become mild, reaching even 13/14 °C (55/57 °F), when Atlantic currents prevail, but the weather in these cases is cloudy and rainy; during these periods, the wind blows frequently, and sometimes can be strong.
On the other hand, there can be cold periods, when north or north-east currents prevail, able to lower the temperature to the freezing point (0 °C or 32 °F), or a few degrees above; in these situations, the feeling of cold can be exacerbated by the wind, which blows moderate, usually from the northeast. The coldest periods occur under the influence of cold air masses from Russia, which can lead to a few days of snow, generally not abundant, and frost. In Paris the temperature rarely drops to around -10 °C (14 °F), but on colder winters this can happen: in January 1985 the temperature dropped to -18 °C (0 °F).

Summer, from June to August, is a pleasantly warm season: the days are very long, and the temperature generally lends itself to outdoor activities. However, the weather is variable: there are some cool and rainy days, due to Atlantic fronts, in which the maximum temperature remains below 20 °C (68 °F), while on other occasions the Azores High can bring some hot and sunny days, maybe a little sultry, with highs around or even above 30 °C (86 °F); in these cases, some thunderstorms can erupt in the afternoon.
Really hot days in Paris are quite rare, though sometimes they may occur, due to hot air masses from Africa: in August 2012 the temperature touched 38 °C (100 °F), while in August 2003, which however has been exceptional in the whole of France, it touched 40 °C (104 °F).

Spring and autumn are cool and unstable, characterized by the passage of Atlantic depressions and by temperature changes. In spring, from March to May, the return of cold weather is possible, with short snowfalls in March and sometimes even in April. Sometimes it's cold still in early May, with highs around 10 °C (50 °F), while during the month the temperature can reach and even exceed 25 °C (77 °F). Autumn, from September to November, is characterized by a gradual increase of cloudy and rainy periods; usually it begins to get cold in November or late October.

Paris

The amount of sunshine in Paris is decent from April to September, and scarce from November to February, when cloudy skies prevail. On average, there are 8 hours of sunshine per day in June and July, and 7 in May and August.

When to go

The best time to visit Paris is from mid-May to mid-September; in particular from mid-May to late June, when the days are long, nature is in bloom and there is a low risk of excessive heat (not by chance, the tennis tournament of "Roland Garros" takes place between the last week of May and the first week of June). However, in this period, but also in mid-summer (July and August), it can rain and it can get cool at night, so it may be useful to bring a sweatshirt or sweater and a light jacket, along with a raincoat or umbrella.
Although the Easter period is a possibility, this time of the year can be quite chilly.