Winter tires are completely serviceable on dry pavement. I'm actually pretty surprised to read that people in the midwest don't regularly switch tires in the winter. The importance of winter tires comes just as much from their behavior in cold temperatures as it does from the different tread pattern. All-season tires use harder rubber compounds that lose nearly all their grip in the cold.

I run winter tires until lows in my area are mostly above freezing, regardless of whether there's any snow on the ground.