Learn Spanish (Latin America): Está nublado porque hay mucha lluvia. - It is cloudy because there is a lot of rain.

In Spanish, we use hace (it makes) for weather that feels like a physical force, like hace calor (it is hot) or hace viento (it is windy). We use está (it is) to describe the current visual condition or state of the sky, like está nublado (it is cloudy).

Could I say es nublado instead?

No, you should use está. In Spanish, we use the verb estar (where está comes from) for temporary states or conditions that change. Since the weather changes day to day, we use está nublado rather than es nublado.

Why is it mucha lluvia and not mucho lluvia?

The word lluvia (rain) is a feminine noun, which we can usually guess because it ends in -a. Words that describe quantity like mucho (a lot) have to match the gender of the noun they belong to, so it changes to the feminine form mucha.

What exactly does hay mean in this sentence?