The day after a late-season snow storm buried the city, police are warning commuters to drive carefully, because roads are still slippery.

From 6 a.m. to 10 a.m., police said they'd responded to approximately 150 collisions.

On Twitter, Ontario Provincial Police have flagged incidents across the Greater Toronto area, from Cambridge to Markham.

Most incidents involve individual vehicles in ditches. The majority of collisions are along high-speed roadways including the Queen Elizabeth Way and Highway 401.

Niagara Regional Police reported a three-vehicle collision on Regional Road 20 near Twenty Mile Road, where a car lost control, crossed the centre line and hit a northbound pickup truck. The truck spun out of control and hit a third vehicle head-on. Two occupants of the third vehicle are deceased.

City crews are working to clear streets, but police are warning drivers that conditions remain extremely slippery.

Environment Canada reports that 14 to 18 centimetres of snow fell across the city, and a sudden dip in the temperature left roads covered in black ice.

Police are urging commuters to leave early, and expect delays. They're also asking drivers avoid distractions like cellphones.

GO Transit is experiencing delays of 30 to 60 minutes due to traffic, and the road conditions have translated to TTC delays as well, as collisions block major roadways.

In addition to snowy roads, the GTA is under an extreme cold weather alert. In the city, the temperature is expected to rise to -7 C in the afternoon, with wind gusts of up to 50 km/h. The low is forecasted as -17 C.

An Environment Canada wind chill warning was in effect for most of southern Ontario, but was dropped shortly after 9 a.m. The weather agency predicted "very cold" winds would draw in "unseasonably cold air" on Wednesday morning. The wind chill dropped temperatures to -27 C.

However, on Friday, the weather agency predicts a dramatic shift: The temperature is expected to rise to 5 C in the afternoon.

Normal temperatures for mid-March range from highs of 4 C to lows of -4 C.

Traffic chaos overnight

From midnight on Wednesday to midnight on Thursday, OPP responded to 682 collisions, including a series of collisions that closed a portion of Highway 401 in Mississauga.

Two tractor trailers collided in the eastbound lanes near Highway 407, and a third tractor trailer jackknifed nearby, blocking the westbound lanes.