Weather in March
I first went to Paris the 3rd week of March in 2001. Weather vacillated between slightly rainy/cold to sunny/cold. But the flowers (Easter lilies?) had JUST sprung up from the ground in the area behind Nôtre Dame. Beautiful! A bit nippy - what I call great walking weather, plus the crowds were smaller, and had a great time. And didn't see too many Americans.
But for me off-season is better as air fares are cheaper ($378 roundtrip from Cincy to London) and I detest hot weather and crowds.
Weather in April
I've also been to Paris in April in 2002 & 2003. In 2002 the Easter Paris weather was rainy, damp, cold, dreary. But in 2003 the entire Easter week was hot & sunny with some rain just on the last day which was Easter Sunday.
So be prepared in Spring to bring layers of clothing & an umbrella. If you get hot you can shed some of those layers; if you get cold then layer up. You never know what the day will bring you. And you just might be pleasantly surprised with some glorious weather!
Photo: March 2001Seeing the flowers in bloom during early spring my first trip to Paris - I couldn't believe they were already coming out in March. Just another reason to go to Paris during the off-season.

