Paris is in the north of France, in the tiny Ill-de-France region, which makes up about 2% of the area of France, but which contains almost 19% of its population. The region generally has France's lowest amount of rainfall, but in Paris those famous showers can come along any time of the year.
The average Paris temperature throughout the year is 53 degrees Farenheit. Rainfall in Paris proper is pretty constant through the year, hovering around 2.3 inches a month, 25 inches yearly. At Paris CDG airport there is considerably more rain.
Spring is the traditional time to go to Paris, and the temperatures are mild and there's plenty of sunlight. Expect some rain. A light sweater should do for most days, perhaps something warmer at night.
Summer weather in Paris is mild and known to be rather changeable, so be prepared. It can swelter in August, when Parisians take to the beaches.
Autumn is perhaps the most romantic time to visit the City of Light, but rainfall begins to increase at the end of August, so prepare accordingly.
Winters can offer a dusting of snow--or a dirty slush if cold, damp weather continues.
The charts below show the historic high and low temperatures in the city of Paris and the month by month rainfall totals.
Paris Hostels (budget)