Hopefully

I see nothing wrong where it follows prior context.

We got rained out today. Hopefully, it won't rain tomorrow.

Do you have a reference saying to avoid it?

The Grammar Curmudgeon has this to say:

Hopefully


The word hopefully is not wrong, but it should be used properly, not as a synonym for "I hope" or "It is to be hoped." Hopefully is an adverb meaning "in a hopeful manner" or "full of hope." We can look forward to our summer vacation hopefully (in a hopeful manner), and

If course this a valid point, but I'd say the use which your man objects to is idiomatic, and clearly more common than the one he advocates.
It's definitely not one of the "incorrect uses" which I object to and carry on the list of pet peeves in my pocket.

I take it as a shorthand for "We are all hopeful that."

Thanks very much for the ref. My AmHtg is 1980's vintage, but I

Ah, yes,

The usage note begins thus:
"As used to mean it is to be hoped, or, let us hope, it is still not accepted by a substantial number of authorities on grammar and usage."

The corollary of that is that some authorities do accept it.

They have a 200 member usage panel and a six-member board of linguists, and they sometimes split on these things.