Hello, I'm trying to get a better understanding of when to use different constructions.

Specifically:

*Si Amalia va al mercado, comprará pescado fresco.*

*Si Amalia fuera al mercado, compraría pescado fresco.*

These two constructions express the same idea. How do we know which one to choose? Is our choice solely based on the probability of the action in the "si" clause?

Thanks.