It's probably snowing in Hokkaido right about now.

Literal

Hokkaido [in-では] about-now snow [subject-が] falling-is probably.

今ごろ ('about now, right about this time') combines 今 ('now') with ごろ (approximate time). Expresses 'at this very moment, approximately.' The ~ている form marks the ongoing present action ('is falling'), and だろう adds modal conjecture.