Wedding in May, how is the weather/rain for an outdoor wedding?

I still have time to decide between an all inside place, and a very nice outdoor space, that has a tent for emergencies. In the case of rain, the reception can be accomodate in the tent, but the ceremenoy would be problematic. What kind of rainy days are there in May? Like, 30 minutes showers, or the three days in a row kind? Any experience with an outdoor wedding in May?