“Most experts agree that motor oils beginning in 5W are the best for winter, especially in climates with extremely low temperatures.
Motor oil is measured in viscosity, which you can see on the labels. For example, 5W-30 would be a type of motor oil viscosity. The first number 5W is what you should be concerned with, as the W refers to winter. In this case, the lower the number, the less viscous the oil during the winter.