Thursday's pileup involved 96 vehicles and closed Highway 400 just south of Barrie, Ont., from 9 a.m. to 6 p.m. Rich Vanderlinde/Barrie Advance/The Canadian Press
It's enough to make the blood of the most experienced winter driver run cold.
One second you're moving along at highway speed with a clear line of sight, the next instant a wall of snow envelops your vehicle, cutting visibility to a few feet.
Although police are still working out the exact cause of Thursday's 96-vehicle pileup on Highway 400 just south of Barrie, Ont., it's believed low visibility caused by snow squalls was a significant factor in the chain-reaction crash that closed the main north-south route out of Toronto for almost nine hours.
No one was seriously hurt in the crash, but it does highlight the danger to drivers posed by snow squalls, which can arrive in an instant.
Snow squalls occur when cold air driven by high winds in cold weather moves over large bodies of water. The cold air mixes with moisture creating blinding driving conditions. Such squalls are common in southern Ontario, which is relatively flat and surrounded by large lakes.
OPP Sgt. Dave Woodford spoke to CBC News and offered the following tips for drivers who suddenly find themselves caught in a squall.
Keep an eye out: Sometimes you can see a snow squall coming. If you see one advancing in the distance toward the highway in front of you, try to pull over somewhere safe. Snow squalls arrive quickly, but they also tend to pass just as fast.
Slow down: We hear it all the time from police but dropping your speed is your best defence in reduced visibility. "You've got to drive to match the conditions," said Woodford, who slowed his cruiser "to a crawl" as he drove through blowing snow while responding to Thursday's pileup.
Don't stop suddenly: Your gut instinct may be to slam on the brakes when a whiteout hits, but this increases your chances of getting rear-ended or sliding off icy roads. Instead, slow down and keep a distance from the car in front of you.
Turn your full lighting system on: In a whiteout, Woodford suggests turning on your vehicle's full lighting system, including four-way flashers, to give other drivers a better chance of seeing you. Many cars have automatic lighting systems and drivers sometimes forget they may have extra lights designed for emergencies and moments of low visibility.
You're in a collision: now what?
So what should you do if you're in a collision in blowing snow?
Woodford said drivers should, if possible, pull over and stay inside their vehicle until emergency crews arrive.
Just as police were dealing with the Highway 400 crash on Thursday afternoon, a smaller but similar chain-reaction crash involving seven cars happened about 60 kilometres south in Stouffville, Ont. A driver is in hospital with life-threatening injuries after he got out of his car following a minor collision in low visibility involving seven vehicles.