
The time to switch from all-season tires over to winter tires is when the temperature starts to stay below 45 degrees, or when there is consistently snow and ice on the road. Normally, all-season tires are the toughest and most useful tire, but in those conditions, winter tires get better.
They are made of a particular blend of rubber that works better in cold temperature. They also have a unique design in their treads that pushes out soft slush and other material, but grips harder on snow and ice than other kinds of tire. However, winter tires don't work as well in the warmth, and they also don't have as long a lifespan as all season tires. So swap them out for all-season versions once it starts to warm up again and clear up.