Paris weather is generally mild. You will not endure Siberian cold nor Arabian heat in Paris.
As the city is not far from the Atlantic Ocean, Paris weather is unstable and, to be frank, unpredictable.
You can never be sure of Paris weather in advance. Never mind. Paris has so much to offer you will very well manage your time on rainy days.
The summer is warm and sunny, sometimes hot. In a big city, summer may not be the most pleasant season. See temperatures in degree fahrenheit on the chart. It may rain heavily during the summer.
The fall has sunny and glorious days with the best light. We love September, the best month in Paris.
Winter is cold in January and February, although it can sometimes be surprisingly mild. It very rarely snows and the snow does not stay long.
Spring is beautiful, when it does not rain too much, which can happen. Parks are gorgeous.
Most months have moderate rains on average. There is not really a rainy season in Paris. But, rain is quite unpredictable. May 2011 was very sunny and May 2012 was very wet. It may be either way next May.