Questions & Answers about Oggi il cielo è nuvoloso.
In Italian you almost always use a definite article with singular, countable nouns—even in general statements. il cielo (“the sky”) is required here.
– Saying Oggi cielo è nuvoloso sounds ungrammatical in everyday speech.
– In very terse weather bulletins you may hear just Nuvoloso or Oggi nuvoloso, but that’s a special, elliptical style.
The grave accent on è marks the third-person singular present of essere (“to be”), distinguishing it from the conjunction e (“and”).
– è = “he/she/it is”
– e = “and”
Omitting the accent would cause confusion with e, so it’s mandatory.