Humidity and Rainfall
Now you see, humidity and rainfall are connected, but not in the way that you'd expect...

Let's suppose that their are rain clouds already in the air, maybe a couple hundred meters to a kilometer or so. Now imagine two scenarios:

1) Humidity of the air is low

2) Humidity of the air is high

Oh, and there is one more thing you need to understand before we move on. As raindrops fall, some of the water will evaporate into the atmosphere, increasing the humidity; but the air can only absorb the water if it has low humidity. Okay, back to our example.

1) Humidity of the air is low


Air can absorb a lot of water
As the rain drops fall, most, if not all of the water will be absorbed (evaporated) in the surrounding air


2) Humidity of the air is high


Air can absorb little to no water
As raindrops fall, the water will not be absorbed into the air


The second example is called rain. The first example is called virga. And yes, when virga happens, some of the rain drops don't even reach the ground! Crazy, right?

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.