Police are investigating the possibility the snowball may have distracted one of the drivers.
One driver had to be cut free from the wreckage after the collision yesterday near Salsburgh, Lanarkshire, and he was rushed to Wishaw General Hospital.
He was being treated for a suspected leg injury, but it is not thought to be serious and the driver of the other lorry was not injured.
The vehicles were travelling on Edinburgh Road, between Newhouse and Shotts.
Police are appealing for witnesses.
Meanwhile, weather forecasters warned that Glasgow could face blizzard conditions tomorrow.