I was about to post some weather links, but
@trecile beat me to it again, with a better link.
i might just add a comment though, that is perhaps somewhat obvious.
Weather in the mountains changes fast. And may look ok from down below, with a different story on the top.
I have crossed the Napoean route twice. On the exact same day. I think it was April 28. 2015 was blue skies. Wonderful views, and bits of snow still remaining.
2018 was cold. Rain. Mist. Strong winds....and about 100 metres visibilty....
The forecasts both times looked ok.