Learn Finnish: Tuolla vuorella saattaa tapahtua lumivyöry. - An avalanche might happen on that mountain.

It expresses probability or possibility, meaning "might" or "may". Like most modal verbs in Finnish, it requires the 1st infinitive of the main verb, which is why we see tapahtua right after it.

Why is the subject lumivyöry at the very end of the sentence?

This is a classic existential sentence. Instead of starting with "an avalanche", Finnish starts with the location (Tuolla vuorella), followed by the verb phrase (saattaa tapahtua), and introduces the new subject at the end. This structure is used to express that something exists or happens in a specific place.

If we were talking about multiple avalanches, would saattaa conjugate to a plural form?

No, it would stay exactly the same. In existential sentences (Location + Verb + Subject), the verb is always in the 3rd person singular, even if the subject is plural. So, "avalanches might happen" would be Tuolla vuorella saattaa tapahtua lumivyöryjä.

What is the difference between using saattaa and just saying ehkä?

Both express possibility. You could say Ehkä tuolla vuorella tapahtuu lumivyöry ("Maybe an avalanche happens on that mountain"). However, saattaa acts as a modal verb directly modifying the action, which often sounds more elegant or integrated in Finnish than simply adding the adverb ehkä.