Weather conditions in Paris equals rain. This situation is similar the whole year, that’s why you should take an umbrella.
You shouldn’t think that these conditions are going to ruin your trip, otherwise it is going to add a little bit more of romanticism to the city.
If you choose summer do not take any coats or winter outfits. But, remember to take them if you choose winter because the temperature is pretty low.
The average temperature is 12º and in summer 30º. During summer months storms can occur but do not worry, they are just temporary.