"The weather is beautiful this weekend."
Translation:Il fait beau, ce week-end.
Because cela is a pronoun, not a determiner, if I have my 'parts of speech' right. "This" acts like an adjective - 'this' weekend, not 'that' weekend. Cela, on the otherhand, can only function like a noun. So, it's more like 'this thing' or 'this one' or (literally), 'this, here' (imagine I'm standing here pointing at it).
So, you can say "Cela est beau": "this is beautiful" as in "this thing, here, is beautiful". Or you can say "Cette chose la est belle" (cette = feminine ce). But you can't say "cela chose est belle".