That's one reason why I store my G-70 from late November - March. I have summer tires (soft compound) and prefer not to mount winter tires since I wouldn't drive it much during the winter months. I do take it out mid March when temps are 30-40, but not for long jaunts. It isn't recommended that I drive with those tires with temps below 40.Compounds are different for various climates. A summer tire will become hard and crack severely if driven in too cold a climate.
As stated, winter tires are soft when the temps goes up. If your son daily drives this car, a set of warm season wheels and tires would be in order. If money aint a thang, just drive it.