Oakville sits on Lake Ontario, which moderates temperatures somewhat but also brings lake-effect snow in winter. The best months to visit are May to October, when the waterfront trail is walkable and the marina is active. June to August is peak season — the Oakville Waterfront Festival runs in late June and draws large crowds to Coronation Park for live music and outdoor events.
Winter is cold (regularly below -10°C in January) and unremarkable for visitors, though GO train access to Toronto makes it a reasonable base even in the off-season. Fall is pleasant and the ravine trails through Sixteen Mile Creek are excellent in October when the leaves turn.