Learn Spanish (Latin America): Hace sol, pero hace mucho viento afuera. - It is sunny, but it is very windy outside.

In English, we use "it is" plus an adjective (like "sunny" or "windy") to talk about the weather. Spanish often uses the verb hacer (to do or to make) plus a noun. So, hace sol literally means "it makes sun," and hace viento means "it makes wind."

In English we say "very windy". Why does the Spanish sentence use mucho (a lot/much) instead of muy (very)?

This goes back to how Spanish treats weather words. Because viento (wind) is a noun, you have to use mucho (much/a lot of) to describe the amount of it. You are literally saying "it makes a lot of wind." The word muy is only used before adjectives and adverbs, not nouns.

Do I really need to repeat hace after the word pero?

Yes, it sounds much more natural to repeat the verb in Spanish. While in English you might just say "It is sunny but very windy," in Spanish you should use the full phrase hace mucho viento to make the second part of the sentence sound complete.

Why does mucho end in an "o" here?

Mucho changes its ending to match the gender and number of the noun it belongs to. Since viento is a masculine, singular noun, mucho stays in its default masculine, singular form.