But now to answer your question...
I'm assuming that your clouds are relatively low to the ground, maybe no more than a kilometer. Also in April, the sun isn't that strong, so it doesn't have a chance to evaporate that much water.
Just remember, all scenarios are different, but as a general rule of thumb, the less humidity, the more rainfall.
EDIT:
This doesn't mean that places with less humidity must get rain. No. Rain cloud formation and humidity are completely unrelated. Rain clouds can form in whatever condition and in any place at any time. Humidity on the other hand affects whether or not the raindrops actually touch the ground.
It'll still rain with low humidity, but the raindrops might get absorbed into the air before they hit the ground. In some cases with low humidity, the sun isn't strong enough to evaporate all the water, so there'll only be a light shower. Sorry for the confusion.