Pine Siskins are irruptive; that is, they aren't reliable migrants and will show up only in some or none of their non-breeding range. There are several other seed eaters that move out of their breeding range based mostly on what food sources are available in their normal haunts.
Here's last year's irruption predictions from a gent who's been doing them for years.
Keep an eye on this link to see when the 2020-21 predictions come out.
And here's more on how Ron Pittaway does it, and on irruption itself.