When does weather change?

That's because you were drifting between 2 level 10 s2 cells.

No reason for the thumbs down. this person is correct.

The weather in each s2 sell will update on the hour. But if you move from one cell to another, then your in game weather will update to that cell immediately when you enter the adjacent cell.

The S2 cells do not obey any municipal boundaries, rivers, or mountains. They are diamond shaped areas that cover the globe, unless you look up where you live and play, you'd never know where the cell boundaries are.