A blast of wintery weather hit Highway 400 north of Toronto Saturday, with predictable results.

The northbound lanes were closed most of the morning after upwards of 40 vehicles were involved in collisons in whiteout conditions.

OPP Sgt Dave Woodford says vehicles were slamming into each other, sliding into ditches and crashing into guardrails.

And Woodford is urging motorists to get into the winter-driving mood, taking extra care as road conditions change.