There are a lot of clouds today. Or... It is very cloudy today.

"There are many clouds". You could also say "It is very cloudy"

This is A1 grammar, Helen. Singular nouns take singular verbs, and plural verbs take plural verbs. It's as simple as that. When a noun can have both countable and uncountable forms, this grammar rule still applies. For example, if you are talking about individual potatoes, you would say 'There aren't many potatoes' (plural). But if you are talking about a large dish of mashed potato, you are using this word in a uncountable sense, so all the grammar words in the phrase have to agree with a singular subject: 'There isn't much potato.' The same goes for 'cloud'. This word is usually countable, but it can, as I told you a few days ago, occasionally be uncountable. So you can say either: "There are many clouds." (plural verb + plural determiner (many) + plural noun) "There is much cloud." * (singular verb + singular determiner (much) + singular noun). You cannot mix singular and plural within your phrase - everything has to agree. It's as wrong to say 'There are much cloud' as it is to say 'There are much book' or 'There are much cat'. The word 'much' and a singular subject can NEVER go with 'are', or with any other plural verb. Likewise, 'many' has to go with a plural noun and a plural verb. This has nothing to do with the essence of what a cloud is, and it has nothing to with concepts of countability. It's just very basic grammar to do with singular and plural. * As a separate point, I'm sure you know that we tend not to use 'much' for affirmative statements in everyday modern English. 'There is much cloud' is correct grammatically, but extremely unnatural. We tend to say 'a lot of' in informal contexts, and phrases such as 'a great deal of' or 'a large amount of' in more formal and written contexts. The uncountable form of 'cloud' is more unusual, and tends to be used mainly in specific contexts, such as weather reports. A weather forecaster, for example, might say 'There won't be much cloud this afternoon' or 'There will be a great deal of cloud.'