Would it be possible/probable for me to leave a message for her?

[phoebemia]

Hi I read the following sentences on a website: (the link is here)
1. Would it be possible for me to leave a message for her?
2. Use public transport whenever possible (= when you can).
3. It is quite possible that the river will flood again.

I got the idea from a web (the link is here), that If something is possible, it can happen. But possible does not mean that something will happen for certain or even that it is very likely to happen.
So is that to say, it's better for those sentences above use probable instead of possible?

 

[Barque]

So is that to say, it's better for those sentences above use probable instead of possible?

"Probable" wouldn't fit in the first two. But it's possible in the third.

It's possible. = It can happen. It may or may not happen.
It's probable. = It's likely to happen.

1. Would it be possible for me to leave a message for her?

You're asking if the other person would be willing to take a message and pass it on to whoever you wanted to speak. You're asking if there is some way a message can be sent to "her". "Probable" doesn't fit. If you used "probable", you'd be asking someone else if you are likely to leave a message for her and that's something only you would know.

2. Use public transport whenever possible (= when you can).

Similarly, "where you can" is very different from "probable".

3. It is quite possible that the river will flood again.

Here, the speaker means that another flood isn't impossible. You could use "probable" and that'd change the meaning. It'd then mean there is very likely to be another flood.