Salzburg to Florence train in November?

Angela which alps are you referring to, Austrian or Italian alps ?

I believe there is still the Nightjet train leaving at 2200 ish and getting into Florence a little after 0600. It makes a few stops on the way, but you won't have to change trains. The fare depends on the accommodations you book (sleeper/couchette). I think reservations are required.

I'm concerned about snow closures.

No risk of snow closures on that route on that or any other rail route across the Alps, These routes are heavily used, major trade routes, and are kept well clear.

The Bernina route was closed for (as far as I can remember) 2 periods of 1-2 days this last winter. That is unusual, and that is not a main route, no freight goes that way, only tourists and locals.

That train is actually running Munich to Rome, as follows:

München Hbf dep 20:10
München Ost dep 20:20
Rosenheim dep 20:50
Salzburg Hbf arr 21:52 dep 22:02
Schwarzach-St.Veit arr 22:52 dep 22:54
Villach Hbf arr 00:19 dep 00:55
Tarvisio Boscoverde arr 01:19 dep 01:35
Bologna Centrale arr 05:17 dep 05:22
Firenze S.M.N. arr 06:14 dep 06:36
Arezzo arr 07:10 dep 07:12
Chiusi-Chianciano Terme arr 07:45 dep 07:47
Orvieto arr 08:10 dep 08:12
Roma Termini arr 09:22

Thanks so much for your reply, this is very helpful to know. We are traveling from Salzburg to Florence and I assumed snow wouldn't be an issue but before planning on it I thought I should check with someone who had more knowledge.